Oil field search technologies. In an effort to increase the amount of oil consumed, people began to dig wells in places of surface oil manifestations, and then drill wells. Exploration of oil and gas fields. Goals and objectives

Prospecting and exploration of oil and gas fields

Exploration work for oil and gas includes all types of human activity- from forecasting the oil and gas content of unexplored territories and to calculating hydrocarbon reserves in identified deposits and deposits and preparing for development. Search and exploration are carried out by specialists of various profiles, including geologists, geophysicists, geochemists, hydrogeologists, hydrodynamicists, drillers, chemists, economists, etc.

At different stages of the exploration process, a set of certain activities and studies is carried out using modern equipment and equipment, including the use of computers and programming, interpretation of aerial and satellite images, drilling of wells for various purposes, testing of reservoirs for oil and gas, etc.

High efficiency of prospecting and exploration of oil and gas accumulations is possible only if sufficiently scientifically based research is carried out in specific oil and gas promising areas and regions, taking into account general patterns formation and placement of oil and gas in earth's crust. When searching for and exploring oil and gas, it is important to take into account economic knowledge, as well as ecology environment, the state of industry and transport in the areas of the proposed prospecting and exploration.

In the projects of prospecting and exploration of oil and gas accumulations in promising areas and areas that are represented by various geological organizations, a justification is given for the economic feasibility of carrying out the work, taking into account the use of the most effective methods, allowing to obtain the maximum increase in proven oil and gas reserves at minimal cost.

Searches for oil and gas in Russia and neighboring countries are carried out on land and at sea (on continental shelf), while the technology of prospecting and exploration works in both cases differs significantly. However, despite the fact that drilling and exploration at sea present greater difficulties compared to similar works on land, in some cases even in continental conditions there are big problems. Thus, technical difficulties and high production costs arise when developing hydrocarbon accumulations at great depths (more than 5 km), as well as under a thick layer of rock salt, as in the Caspian region (both together).

In the projects of prospecting and exploration of oil and gas accumulations, in addition to the technological part, which sets out the tasks, types, scope and methodology of all work, there are environmental and economic parts that provide for the implementation of measures to protect the subsoil and the environment, as well as assessing the geological and economic significance designed works. After the discussion and approval of the projects, material, technical, labor and other resources are allocated for the exploration of oil and gas.

At the end of the prospecting and exploration process, scientific processing of all the information received is carried out, hydrocarbon reserves are calculated, and a geological report is compiled. As a result, the degree of implementation of the project is determined and the geological efficiency of the conducted exploration work is assessed, and then economic indicators are calculated.

The search and exploration of oil and gas, as well as the development of their accumulations, is carried out by various organizations, most of which are last years transformed into joint-stock companies (JSC), for example, in the Tyumen region of Western Siberia: OJSC Rosneft-Purneftegaz, OJSC Surgutneftegaz, OJSC LUKOIL-Kogalymneftegaz, etc.

Thus, the exploration process associated with the search and exploration of oil and gas accumulations consists of a set of works that should ensure the discovery of a hydrocarbon deposit, its geological and economic assessment and preparation for development.

At the same time, a geological study of the subsoil is necessarily carried out, which provides for the rational use of funds allocated by the state, JSC or other customers of the work. Unfortunately, during the production of geological exploration for oil and gas, in some cases, significant damage is caused to the environment, while not only nature, animals and vegetable world, but also agricultural land, as well as people directly involved in prospecting and exploration, living in areas of discovered oil and gas fields. Thus, the development of the wealth of Western Siberia and the direction of exploration work further north to the tundra regions brought complications to the life of the northern peoples engaged in reindeer herding, due to the search for new pastures, etc. Or another example - the Astrakhan gas condensate facility in the Caspian region, where the gas has a high content of sulfur compounds, which, of course, negatively affects the people living and working there.

Therefore, the successful implementation of prospecting and exploration for oil and gas should include a set of necessary measures to prevent contamination of land, air and water sources, as well as forests, farmland and other elements of the environment. Compliance with environmental standards is necessary in all types of human activity, including prospecting, exploration and development of hydrocarbons.

The prospecting and exploration process for oil and gas includes three successive stages: regional, prospecting and exploration, each of which is divided into two stages

. Regional Stage is carried out in unexplored and poorly explored regions or their parts, as well as when searching for hydrocarbon accumulations in deep-seated poorly explored parts of the section, for example, under rock salt at depths of more than 4 km, as in the Caspian region.

At the stage of forecasting oil and gas potential, the study of lithological and stratigraphic complexes of the sediment section, the identification of structural floors, the study of the main stages of the tectonic development of the study area and tectonic zoning are carried out. Consequently, at this stage, the main features of the geological structure and geological history. Then, oil and gas promising horizons and zones of possible oil and gas accumulation are identified. Next, a qualitative and quantitative assessment of the prospects for oil and gas content is carried out, as well as a choice of the main directions and priority objects for further research.

At the next stage estimates of oil and gas accumulation zones the oil and gas geological zoning is specified, the largest traps are identified, for example, swell-like uplifts , with which oil and gas accumulation zones can be associated . A quantitative assessment of the prospects for oil and gas bearing is carried out, and areas and priority objects (regional traps) are selected for prospecting.

Search stage comes when the regional stage is fully completed and a geological justification has been carried out for the implementation of prospecting for oil and gas at the identified promising regional trap. It is possible to open a zone of oil and gas accumulation in it, including a number of oil and gas fields within individual areas - local uplifts or other local traps that complicate the regional trap. The search stage is divided into two stages, the first of which is in turn divided into two substages.

The stage of identifying and preparing objects for exploratory drilling is divided into sub-stages: 1 - identification of objects and sub-stage 2 - preparation of objects. At the first substage, the occurrence conditions and parameters of promising reservoirs are identified, as well as the most promising local traps (objects, areas), priority objects are selected and they are prepared for exploratory drilling. For example, if a swell is a regional trap, then the largest and most well-prepared for drilling local structures (anticlines, domes) are selected, among which the sequence of their preparation for exploration drilling is outlined. The structures most prepared for drilling are those that, according to field geophysical surveys, are quite clearly defined in size (length, width, amplitude), configuration and arch of the structure, as well as the position of structural complications (faults, etc.), if a complex structure is identified.

Large traps include uplifts with an area of ​​50-100 km 2 or more, medium traps - 10-50 km 2, small ones - up to 10 km 2. At the same time, structures whose resources exceed the reserves of the average in the area of ​​the deposit are chosen as priorities. In addition, economic indicators (proximity to deposits, pipelines, remoteness from deep drilling bases, depth of productive formations, hydrocarbon quality, etc.) also affect the sequence of entering structures into exploration drilling. At the second sub-stage, the following is carried out: specification of the identified promising traps; selection of objects and determination of the sequence of their input into exploration drilling; quantitative assessment of hydrocarbon resources at sites prepared for exploratory drilling; selection of locations for exploratory wells at prepared sites.

At the stage of prospecting for deposits (deposits) the main goal is the discovery of hydrocarbon accumulations: the discovery of a deposit or the identification of new deposits in an unexplored part of the section within the fields that are under exploration. The complex of tasks to be solved at this stage includes: identification of productive reservoirs covered by impermeable layers (tires); determination of reservoir parameters; sampling and testing of productive horizons and wells; obtaining industrial inflows of oil and gas; determination of reservoir properties of formations and physical and chemical properties fluids (oil, gas, condensate, water); assessment of hydrocarbon reserves of discovered deposits; selection of objects for detailed and appraisal work.

exploration stage is the final in exploration work for oil and gas. Exploration is carried out in areas where industrial inflows of oil and gas have been obtained. The purpose of exploration work is to evaluate open accumulations of oil and gas and prepare them for development.

At the first stage of exploration (assessment of deposits or deposits), the following is carried out: determination of the parameters of deposits and deposits in order to establish their industrial significance; calculation of hydrocarbon reserves of deposits and fields; selection of objects and exploration floors; determination of the sequence of pilot operation and preparation of objects for development.

At the next stage of exploration (preparation of sites or deposits for development), the main tasks are: geometrization of hydrocarbon deposits; assessment of the reliability of the values ​​of reservoir properties of productive layers and estimated parameters for calculating reserves and compiling technological scheme developments for an oil facility or scheme for pilot operation of a gas facility; calculation of hydrocarbon reserves and determination of the recovery factor (oil recovery); additional study of deposits and deposits in the process of development.

In the search and exploration of oil and gas, various research methods are used in combination, including: geological, geophysical (field and borehole), geochemical, hydrogeological, geothermal, hydrodynamic, remote, geomorphological, mathematical methods, the use of computers and programming. Therefore, various specialists participate in the exploration process: geologists, drillers, geophysicists, geochemists, hydrogeologists, hydrodynamics, mathematicians and others.

The main types of research are geophysical research

There are currently four main geophysical methods in use

research: seismic, gravimetric, magnetic and electrical.

Seismic exploration is based on the study of the propagation of elastic vibrations in the earth's crust. Elastic oscillations (or, as they are also called, seismic waves) are most often caused artificially. Seismic waves propagate in rocks ax at a speed of 2 to 8 km / s - depending on the density of the rock: the higher it is, the more speed wave propagation. At the interface between two media with different densities, part of the elastic oscillations is reflected and returns to the Earth's surface. The other part is refracted, overcomes the interface and goes deeper into the bowels - to a new interface. And so on until it finally fades away.

Reflected seismic waves, having reached the earth's surface, are captured by special receivers and recorded on recorders. Having deciphered the graphs, seismic prospectors then establish the boundaries of the occurrence of rocks. Based on these data, maps of the underground relief are built.

Fig.28 Scheme of seismic survey

This method of reflected waves was proposed by the Soviet geologist V.S. Voyutsky in 1923 and is widely used throughout the world. At present, along with this method, the correlation method of refracted waves is also used. It is based on the registration of refracted waves formed when an elastic wave falls on an interface at a certain pre-calculated critical angle. Used in the practice of seismic surveys and other methods. Previously, explosions were most often used as a source of elastic vibrations. Now they are being replaced by vibrators. The vibrator can be installed on a truck and a fairly large area can be surveyed in a working day. In addition, the vibrator allows you to work in densely populated areas. Explosions would certainly disturb the inhabitants of nearby houses, and vibrations can be picked up at such a frequency that they are not perceived by the human ear. The only drawback of this method is the shallow depth of research, no more than 2-3 kilometers. Therefore, for more in-depth studies, an explosive energy converter is used. The source of the waves here is essentially the same explosion. But it no longer occurs in the soil, as before, but in a special explosive chamber. The explosive impulse is transmitted to the ground through a steel plate, and instead of explosives, a mixture of propane and oxygen is often used. All this, of course, makes it possible to greatly speed up the process of subsurface sounding.

The gravimetric method is based on the study of changes in gravity in a given area. It turns out that if there is a low-density rock under the soil surface, for example, rock salt, then the earth's gravity here also decreases somewhat. But dense rocks, such as, for example, basalt or granite, on the contrary, increase the force of gravity.

These changes are set by a special device - a gravimeter. One of its simplest variants is a weight suspended on a spring. Gravity increases - the spring stretches; this is fixed by a pointer on the scale. Gravity decreases, the spring contracts accordingly. And how does oil and gas deposits affect the Earth's gravity? Oil is lighter than water, and rocks saturated with oil or its indispensable companion, gas, have a lower density than if water were placed in them. This is measured with a gravimeter. However, such gravitational anomalies can also be caused by other reasons, such as the occurrence of rock salt layers, as we have already said. Therefore, gravity exploration is usually supplemented with magnetic exploration.

Our planet, as you know, is a huge magnet, around which there is a magnetic field. And this field can be effectively influenced, among other things, by the rocks occurring in the area. For example, deposits iron ore were discovered due to the fact that the pilots of the planes flying here were surprised at the strange behavior of the magnetic needle? Now this principle is also used to search for other types of minerals, including oil and gas.

The fact is that oil very often contains impurities of metals. And, of course, the presence of metal is felt, though not by a "magnetic needle", but by modern highly sensitive devices - magnetometers. They allow you to probe the bowels of the earth to a depth of up to 7 kilometers.

Another geophysical method for prospecting for minerals, electrical exploration, was developed in 1923 in France and is still used today. Actually, this is a kind of magnetic reconnaissance with the only difference that changes are recorded not in the magnetic, but in the electric field.
Since there is practically no natural electric field on Earth, it is created artificially, with the help of special generators, and the desired area is probed with their help. Typically, rocks are dielectrics, that is, their electrical resistance is high. But oil, as we have already said, may contain metals that are good conductors. The decrease in the electrical resistance of the subsoil serves as an indirect sign of the presence of oil.

In recent years, another method has become increasingly widely used - electromagnetic exploration using magnetohydrodynamic (MHD) generators. Depths of several kilometers have become available to electromagnetic waves when minerals are being searched; up to hundreds of kilometers when it comes to general studies of the earth's crust.
The heart of a modern MHD generator is a rocket engine powered by gunpowder. But this gunpowder is not quite ordinary: the electrical conductivity of the plasma it creates is 16,000 times higher than conventional rocket fuel. The plasma passes through the MHD channel located between the magnet windings. According to the laws of magnetodynamics, an electric current arises in a moving plasma, which, in turn, excites an electromagnetic field in a special emitter - a dipole. With the help of a dipole, the sounding of the Earth takes place.
In just a few seconds, the MHD facility develops a power of tens of millions of watts. And at the same time, it does without bulky cooling systems, which would be inevitable when using traditional radiation sources. And the installation itself is several times lighter than other types of power generators.
The efficiency of the MHD unit was first tested in the late 1970s in Tajikistan. Then, in the area of ​​the Peter I Ridge, scientists conducted the first experiments on MHD sounding, trying to catch signs of an approaching earthquake. The signals of the powerful 20-megawatt Pamir-1 installation were recorded at a distance of up to 30 kilometers from it. A little later, MHD installations were used to search for oil and gas fields. To begin with, a fairly well-known oil region was chosen - the Caspian lowland. Thanks to MHD sounding, another opportunity has appeared not only to determine the presence of oil and gas bearing layers, but also to clearly delineate deposits. But usually for this you have to drill several expensive wells.
Having received the first reliable information about the reliability of the MHD method, scientists did not limit themselves to exploration in the Caspian lowland. New way geophysical exploration of subsoil was used on the Kola Peninsula, on the shelf Barents Sea- in areas with thick layers of sedimentary rocks, in which oil usually hides. An analysis of the data obtained showed that the occurrence of oil here is quite likely.

There are many geophysical methods used by oil explorers. However, none of the methods gives a 100% indication of the presence of oil. So you have to use them in combination. To begin with, magnetic reconnaissance is usually carried out. Then supplement it with gravimetric data. Then the methods of electrical and seismic prospecting are used. But even this is often not enough for an accurate answer. Then geophysical methods are supplemented by geochemical and hydrogeological studies.
Among the geochemical methods, first of all, gas, luminescent-bituminological and radioactive surveys should be noted.

Gas photography was developed in 1930. It was noticed that around any deposit, as it were, the lightest fog is formed - the so-called scattering halo. Hydrocarbon gases penetrate through the pores and cracks of rocks from the depths of the Earth to the surface, while their concentration in soil waters and upper layers of the rock increases. Having taken a sample of soil and soil water, the oil explorer, using a sensitive gas analyzer, establishes an increased content of hydrocarbon gases, which is a direct indicator of the close location of the deposit.
True, in order for this method to work reliably enough, devices of the highest sensitivity are needed - they must reliably detect one impurity atom among ten or even a hundred million others! In addition, as practice shows, gas anomalies can be displaced in relation to the deposit or simply point to small deposits of no commercial value.
Therefore, they try to supplement this method, for example, with luminescent-bituminological survey. Its principle is based on natural phenomenon. Above the oil deposits, the content of bitumen in the rock has been increased. And if a rock sample is substituted under a source of ultraviolet light, then the bitumens immediately begin to glow. According to the nature of the glow, its intensity determines the type of bitumen and its possible connection with the deposit.

Radiation photography is based on another natural phenomenon. It is known that in any region there is a so-called radioactive background - a small amount of radiation due to the impact on our planet of cosmic radiation, the presence of radioactive transuranium elements in its bowels, etc. So, experts managed to discover an interesting pattern: the radioactive background decreases over oil and gas deposits. For example, for the South Mangyshlak deposits, such a decrease is 1.5 - 3.5 µCi/hour. Such changes are quite confidently recorded by existing instruments. However, this method is still of limited use.

Classical exploration methods are very expensive: their average world cost at the exploration stage is 3,000-5,000 dollars per 1 km 2 Therefore, other methods are used, for example, geomorphological exploration methods.

Prospecting and exploration work is carried out in order to discover an oil or gas field, determine its reserves and draw up a development project. In this case, the search work is divided into several stages:

1) general geological survey;

2) detailed geological survey;

3) deep drilling of exploration wells.

At the first stage, which is called a general geological survey, a geological map of the area is compiled. Mining at this stage is not done, only work is carried out to clear the area to expose bedrock. The general geological survey provides some insight into the geological structure of modern deposits in the study area. The nature of the occurrence of rocks covered by modern sediments remains unexplored.

At the second stage, called a detailed structural-geological survey, mapping and structural wells are drilled to study the geological structure of the area. Mapping wells are drilled to a depth of 20 to 300 m to determine the thickness of sediments and modern deposits, as well as to establish the form of occurrence of layers composed of bedrock. Based on the results of a general geological survey and mapping drilling, a geological map is built, on which the distribution of rocks of various ages is depicted by symbols. For a more complete picture of the area under study, the geological survey is supplemented by a consolidated stratigraphic section of deposits and geological profiles.

native breeds. Based on the results of a general geological survey and mapping drilling, a geological map is built, on which the distribution of rocks of various ages is depicted by symbols. For a more complete picture of the area under study, the geological survey is supplemented by a consolidated stratigraphic section of deposits and geological profiles.

The summary stratigraphic section, drawn as a column of rocks, should contain a detailed description of the rocks that make up the area under study.

Geological profiles are built in a cross-stretch of rocks to depict the geological structure of the site in vertical planes. For a detailed clarification of the nature of the bedding or, as they say, to study their structural form, in addition to the geological map, a structural map is built according to the data of specially drilled structural wells. The structural map reflects the surface of the reservoir of interest to geologists and gives an idea of ​​the shape of the reservoir using contour lines. Build a structural map as follows (Fig. 1.6). The investigated surface separating the layers Ai B, mentally dissected by horizontal planes located, for example, 100 m apart, starting from sea level. The lines of intersection of horizontal planes with the surface of the reservoir on a certain scale are laid out on the plan. Before the figure showing the depth of the secant horizontal surface, put a plus sign if the section is above sea level, and a minus sign when it is below sea level. At the second stage, geophysical and geochemical methods are also carried out, which make it possible to study the structure of the subsoil in more detail and more reasonably identify areas that are promising for deep drilling in order to search for oil and gas deposits. Of the geophysical methods, seismic and electrical exploration are the most common. Seismic exploration is based on the use of patterns of propagation of elastic waves in the earth's crust, artificially created in it by explosions in shallow wells. Seismic waves propagate along the surface of the Earth and in its depths.

Some of the energy of these waves, having reached the surface of dense rocks, will be reflected from it and returned to the surface of the Earth. Reflected waves are recorded by special instruments - seismographs. According to the time of arrival of the reflected wave to the seismograph and the distance from the place of explosion, the conditions for the occurrence of rocks are judged.

Electrical prospecting is based on the ability of rocks to pass an electric current, i.e., on their electrical conductivity. It is known that some rocks (granites, limestones, sandstones saturated with saline mineralized water) conduct electricity well, while others (clays, sandstones saturated with oil) practically do not have electrical conductivity. Naturally, rocks with poor electrical conductivity have higher resistance. Knowing the resistance of various rocks, it is possible to determine the sequence and conditions of their occurrence by the nature of the distribution of the electric field.

Electrical methods for studying the Earth's interior are widely used in the study of sections in drilled wells during well electrometry. To do this, three electrodes are lowered into the well on a special logging cable, and the fourth one is grounded on the surface near the mouth. Then turn on the electric current. Via special devices the potential difference is measured throughout the well, while the apparent resistivity diagram and the potential curve are recorded. Against such rocks as limestones and oil-saturated sandstones, a significant apparent resistance is recorded, against clays and water-bearing sandstones, incomparably lower resistances are noted. Since the fluid in the well is not isolated from the reservoir, due to the pressure drop, it can move from the well into the reservoir and back. As a result of the movement of salty mineralized water through porous rocks, polarization occurs and a natural electromotive force. In more permeable rocks, the fluid moves faster and, therefore, there is a large difference in natural potentials. For example, when a fluid passes through highly permeable sands, a much larger natural potential difference occurs than when a fluid moves through poorly permeable clays and dense limestones. Thus, in the process of well electrometry, with the help of special instruments, apparent resistivity and natural potential differences are measured and automatically recorded. By comparing the readings, the depth and thickness of the sandstone saturated with oil, characterized by large values ​​of apparent resistivity and natural potential difference, are established. Among the field geophysical methods, gravity and magnetic prospecting are also known, and among the well survey methods - radiometry, etc.

The use of geophysical methods makes it possible to identify structures favorable for the formation of oil and gas traps. However, not all identified structures can contain oil and gas. Select from total number discovered structures most promising without drilling wells help geochemical methods of exploration of the subsoil, based on the conduct of gas and bacteriological surveys. Gas imaging is based on the diffusion of hydrocarbons that make up oil. Each oil or gas reservoir releases a stream of hydrocarbons penetrating through any rock. With the help of special geochemical instruments, the content of hydrocarbons in the air in the area under study is determined. Above the oil and gas deposits, the instruments show an increased content of hydrocarbons. Gas survey results simplify the selection of a site for detailed exploration by drilling.

Bacteriological survey is based on the search for bacteria contained in hydrocarbons. Analysis of soils in the area under study makes it possible to detect the places of accumulation of these bacteria, and, consequently, hydrocarbons. As a result of bacteriological analysis of soils, a map of the location of the proposed deposits is compiled. Thus, the results of gas and bacteriological surveys complement each other, which ensures the reality of planning drilling operations in the area under study.

After carrying out a complex of geophysical and geochemical studies, they begin third stage exploration work - deep drilling of exploration wells. The success of prospecting work at the third stage largely depends on the quality of work carried out at the second stage. In the event that oil and gas are obtained from a prospecting well, exploration work ends and detailed exploration of an open oil or gas field begins. So-called contouring, appraisal and control and research deep wells are simultaneously drilled in the area to determine the size (or contour) of the deposit and control the progress of exploration of the deposit. After drilling the required number of deep wells for exploration of the field, the period of prospecting and exploration works ends and the period of drilling production wells inside the oil-bearing (or gas-bearing) contour begins, through which oil or gas will be extracted from the bowels of the Earth.

RESERVES OF DEPOSITS

The reserves of oil, combustible gases and the components contained in them are divided into two groups according to their national economic significance, which are subject to separate calculation and accounting:

1) balance - reserves that meet industrial standards and mining and technical operating conditions; their development is economically feasible (these reserves are called geological);

2) off-balance - reserves, the development of which at this stage is unprofitable due to their small number, the complexity of operating conditions, poor quality of oil and gas or low well productivity.

According to the balance reserves, recoverable reserves are calculated, that is, those that can be extracted from the bowels by methods that correspond to the current level of technology and technology.

According to the degree of exploration of the fields, the reserves of oil, gas and related components are divided into four categories: A, B, C, C 2 .

Category A includes reserves calculated on the area explored in detail and delineated by wells that have produced commercial oil and gas flows. To calculate the reserves of this category, the parameters of the reservoir, its productivity, the boundaries of the reservoir, the properties of oil and gas, as well as the content of associated components in them (from geological and geophysical results and the results of trial operation of many wells) should be well known. The reserves of this category are determined during the development of the deposit.

Category B includes reserves calculated on the area, the commercial oil or gas content of which is proven when drilling wells with favorable production and geophysical indicators, provided that these wells have penetrated the reservoir at different hypsometric marks and commercial oil flows have been obtained in them. When calculating category B reserves, the geological and field characteristics of the reservoir, its productivity, oil and gas bearing contours, and the properties of gas-liquid mixtures should be approximately studied to the extent sufficient to draw up a development project.

Category C includes reserves of deposits, the oil and gas content of which is established on the basis of obtaining industrial inflows of oil or gas in individual wells and favorable production and geophysical data in a number of other wells, as well as reserves of a part of the deposit (tectonic block) adjacent to areas with reserves of higher categories.

In a rational complex of exploration work for oil and gas, the exploration stage, as can be seen from the table of the rational sequence of these works, is a natural continuation of the exploration stage. Exploration work is aimed at industrial evaluation of deposits and deposits discovered at the exploration stage and preparing them for development. At the same time, hydrocarbon reserves of industrial category C1 obtained as a result of exploratory drilling and preliminary estimated reserves of category C2 must be transferred to industrial ones over the entire area of ​​the discovered field or deposit.

The main types of exploration work are: drilling and testing of exploration wells, analysis of all the necessary geological and geochemical information to clarify the parameters of the deposit (deposit) and prepare it for trial operation. If necessary, borehole seismic exploration by the CDP method and, to a small extent, field geophysical methods can be provided.

The main methodological principle of exploration, formulated by G.A. Gabrielyants and V.I. Poroskun back in 1974, is the principle of drilling uniformity, which is implemented by uniform placement of exploration wells over the volume of the deposit. According to this principle, detailed study first of all, those parts of the deposit (fields) that contain the main reserves of hydrocarbons. At the same time, the accuracy of reserves estimation increases, and, consequently, the quality of field preparation for trial operation and subsequent development. At the same time, a differentiated placement of exploration drilling is envisaged, taking into account the morphogenetic features of the deposit or deposit structure.

Modern exploration of oil and gas fields takes into account the principles of optimization and universality of the exploration drilling process, first proposed by V.M. Kreiter and V.I. Biryukov (1976). These principles are formulated as follows:

1. The principle of a rational system and completeness of studies of a separate deposit or deposit.
2. The principle of successive approximations in the study of a deposit or a separate deposit.
3. The principle of relative uniformity in the study of the object of reconnaissance.
4. The principle of the least labor, scientific, applied and material and technical costs.
5. The principle of the least expenditure of time and the achievement of the greatest savings while observing energy-saving technologies.

A rational system for exploration of oil and gas fields involves drilling a certain, usually minimal, number of exploration wells, laid in a certain sequence to obtain information necessary and sufficient for the industrial evaluation of a discovered field and preparing it for development. At the same time, the system for placing exploration wells should correspond to the peculiarities of the geological structure of the object under study.

The section of an open deposit (deposit) is divided into exploration floors. The exploration level is understood as a part of the sedimentary cover section, which includes one or more productive layers located at close hypsometric levels and characterized by similarity in geological structure host rocks and the physical properties of hydrocarbon fluids. Their exploration can be carried out with one grid of wells.

There are three systems and corresponding methods of exploration drilling: triangular, ring and profile with a system of parallel transverse and longitudinal profiles of exploration wells.

Triangular exploratory drilling placement system. This technique is the oldest and was used at the dawn of development oil industry. At the same time, as can be seen from Fig. 65, the first exploratory well is located in the most optimal structural and hypsometric conditions, the rest are laid as exploration in the form of equilateral triangles with a side whose length should not exceed 500 meters at angles of inclination of the local uplift wings up to 10 degrees. At 20 degrees of inclination, it decreases to 400 meters, then decreases by about 50 meters with an increase in the angle of inclination of the wings by every 5-6 degrees.

The irrationality of the accepted triangular system of placement of exploratory wells, even with the accepted maximum distances between them of 500 meters, consists in drilling an unnecessarily large number of them to comply with the indicated principle of uniformity. This leads to a significant increase in the cost of drilling. The process is justified to a certain extent with the achievement of a very modest geological efficiency (up to 80-100 standard tons per 1 meter of exploration drilling) only if the trap area and the predicted deposit are no more than 2-2.5 km2. Exploration experience of identified lithological and stratigraphic hydrocarbon accumulations up to 1-1.5 km2 in size also indicates the profitability of the triangular exploration drilling system.

In the United States, along with large bay-like lithological-stratigraphic deposits, small lithologically limited, or "laced", or lenticular, accumulations of oil and gas with recoverable reserves of up to 1.5 million conventional units are widespread. t with sizes up to 1.5-2 km2. For the exploration of such deposits, a triangular grid of wells is also used with their number from 12 to 15, which is within the limits of profitability with an average efficiency of up to 120 conventional units. t/m. In Russia, a similar system of exploratory drilling placement was successfully used as a rational one in 1912 on initial stage exploration discovered for the first time in world practice by I.M. Gubkin "sleeve-shaped" oil deposits with the transition from 1916 to profile drilling. At present, this exploration technique is used in the exploration of small oil deposits associated with pre-Visian and pre-Tournaisian erosion "incisions" within the Volga-Urals and neighboring oil and gas regions from the south.

Ring system for exploratory drilling. The rational nature of the ring system of exploration of open deposits and deposits, which is successfully combined with the development of individual explored floors, is confirmed by the example of the unique Zapolyarnoye gas condensate field with a total area of ​​over 2,000 km2 and a recoverable gas reserves of 1.5 trillion cubic meters. m3. In general, prospecting was carried out using the “cross exploratory drilling” system with 12 exploratory wells, and exploration was carried out by 27 exploratory wells, placed according to the annular technique shown in fig. 66.

The specificity of the ring system is determined at the Zapolyarnoye field by the following position of the wells in the structural interisogypsum fields. Within the first field of the discoverer from well 1, 4 drilling rigs are laid. After contouring the inner area of ​​the field in the next more external field in relation to the already contoured central zone, 5 drilling rigs are designed, marked with squares. Having completed the delineation of this part of the deposit, it is planned to develop outer zone gas condensate field with the laying of first 7 exploration wells in the penultimate field, and then 9 - in the last interisogypsum contour framing the field.

The rational nature of the ring system of exploration drilling in the development of the unique Zapolyarnoye gas condensate field is confirmed by the achieved value of geological efficiency, which exceeds 1000 conventional units here. tons per 1 m of exploration drilling.

Hence, high efficiency The use of the ring system is achieved by the presence of large (up to gigantic and more) hydrocarbon reserves and the relatively simple structure of the field with a deposit of a reservoir or massive structure of the dome type. This should, first of all, be guided by when choosing a rational methodology for exploration, which, as can be seen from the example of the unique Zapolyarnoye field, is fully justified by the results obtained. The ring system was used in the exploration of a number of large gas condensate fields in the Yeisk-Berezan gas-bearing region, in particular Kanevskoye and Leningradskoye. In the United States, this technique was used to explore the main arched deposit in the limestones of the Arbocle Formation in the largest oil field Oklahoma City in the Western Inland Province.

Profile system for placement of exploration wells

In modern
Under natural conditions for the exploration of oil and gas deposits and deposits of anticline and non-anticlinal types of any complexity of structure, except for the cases noted above in the first methods, the most effective and universally rational is the profile system of exploration drilling. Its essence lies in the design of a certain number of exploratory wells, each laid at the intersection points of transverse and longitudinal profiles. Moreover, depending on the size of the explored deposit, the distance between the transverse and longitudinal profiles and the area per one projected drilling well are strictly regulated. Compared to previous methods, the profile method is the most “flexible”, allowing current changes in the rational grid of wells and, thus, the coverage area of ​​the explored part of the field.

Consider typical examples placement of exploratory wells according to the profile system. On fig. 67 shows the location of wells in a gas condensate field. A larger eastern block was introduced into exploration using the profile method, and the rational area for each well reaches 26 km2. The position of the wells on the profile is shown on the example of the central part of the explored block. The total number of wells for the eastern block of the field is 38. With the same selected parameters, the rational number of exploration wells for the smaller western gas condensate reservoir with the same GWC mark will be 26. However, given the gas condensate type of hydrocarbon fluid and the possibility of one and a half increase in the distances between profiles and area per well, the total number of wells in the eastern block without violating the principle of rationality can be 25, and for the western deposit - 18.

On fig. 68 shows a rational technique for an anticlinal block
30x70 km in size, complicated by faults and including an oil deposit
with a mark of VNK minus 1590 m. Here, the most rational placement is
subsidiaries along a system of parallel mutually perpendicular profiles
with the area of ​​each square 18 km2.

The position of the profiles and wells is shown on the example of the central part of the western dome of the anticline.

On the example of the central part of the deposit, a rational placement of exploration wells for the western larger block of the anticline trap with a predicted oil deposit at an OWC level of minus 3200 meters is given. As the most rational method, a technique similar to that noted above was adopted, with an area of ​​individual squares of a grid of wells of 10 km2 and a number of wells of 12, starting with a exploratory well-the discoverer of the field. For reconnaissance shown in Fig. 69 and 70, respectively, of the predicted gas condensate and oil fields, a rational well placement system is considered for productive blocks.

From exploration well 1, which gave industrial inflows of gas condensate and oil, it is planned to develop a rational grid of designed drilling rigs while maintaining the “square” placement principle. For the explored gas condensate field, the area per well is 12 km2, taking into account the gas condensate type of hydrocarbon fluid, instead of 8 km2 for oil, and the rational exploration complex includes 24 wells.

Exploration development of other blocks of the field should not provide for an increase in the number of drilling rigs. As rational for a larger predicted oil deposit (Fig. 70) with an OWC mark of minus 2400 m, it is also envisaged in the central part of the structure from exploration well 1 according to the scheme shown in the figures above; an area of ​​28 km2 per rig was taken as more efficient, and total exploration wells - 32. Further, according to the same scheme, exploration is carried out with 16 wells of a smaller, central structural block.

On fig. Figure 71 shows a gas condensate deposit of a dome type with a GWC elevation of minus 1050 m, complicated in the central part by a horst limited by the surfaces of the fault planes in the form of two beams.

The most rational for the exploration of this field will be sequential drilling according to the profile-square scheme, first in the central part of the deposit with an area of ​​8 km2 per well, starting from a horst. Outside the horst, the distance between wells can be increased up to 3 km, and the area per drilling rig can be increased up to 10 km2. The rational number of wells for exploration of the deposit should not exceed 20. For the western smaller block - 12 wells.

For the exploration of an oil deposit of a domed type in an anticline trap complicated by a fault from the south (Fig. 72), with an OWC mark of minus 2810 meters with an area of ​​18x6 km, the same square rational grid of wells with an area of ​​5 km2 is used. Exploration well 1 is the starting point for exploration. The minimum number of wells to fully cover the deposit with the transfer of resources to category C1 will be 20.

Exploration of arched oil deposits, depicted in fig. 73 and 74 is carried out according to a similar profile system with an area of ​​4 km2 per exploration well. The total area of ​​the field, as well as the morphostructural conditions as a whole, are identical to the deposits (Fig. 70 and 71), using also as a basis for placing a rational scheme of drilling in the central part of the deposit with exploration well 1.

On fig. 75 shows a gas condensate reservoir of a complex structure of a domed tectonically screened type with a GWC mark of minus 775 meters. The rational placement of exploratory drilling provides for the laying of exploratory wells in the central block from well 1 along a grid of 8 km2 (before GWC) of ten wells, which makes it possible to count on the most effective exploration of the field with an index of at least 500 conventional units. tons per meter of exploration drilling.

An example of a rational exploration of a near-contact type oil deposit confined to a diapir brachianticline is shown in Fig. 76.

Within the deposit, a rational grid of drilling rigs is designed according to the specified profile scheme with an area per well of 6 km2. The project provides, as can be seen from the figure, the drilling of 30 exploration wells up to the OWC at a mark of minus 3300 m, starting from the exploration well 1, the discoverer of the field.

For the deposits of structural-lithological and structural-stratigraphic types considered above, the same profile system of placement of exploratory wells with the specified square grid remains rational. At the same time, the area per well varies from 5 km2 for medium-sized deposits to 18 km2 for large ones.

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The most valuable natural resource - oil - is revealed through an active search for deposits. Its largest explored reserves are concentrated in the Middle and Near East, Africa, Latin and North America, South-East Asia. website

What is the purpose of finding oil deposits? First of all, reserves are analyzed, then they are comprehensively prepared for technical development. The work is accompanied by geophysical, hydrogeochemical, geological measures to identify deposits, drilling of openings and their detailed study are also carried out.

General training

At the first stage, geological search technologies are used - specialists survey the territory, organize field work. The latter consist in the analysis of rock layers, designing the angle of inclination. As a result of processing the obtained data, sections of the terrain and geological maps are compiled. www.site

Features of geophysical methods of oil prospecting

There are several technologies here:

• gravity exploration,
• magnetic prospecting,
• seismic exploration,
• electrical exploration. https://www.site/

Seismic exploration is reduced to the use of elastic waves of artificial origin - the researchers look at how they are distributed in the earth's crust.

Gravity exploration is based on the relationship between the earth's gravity and the level of saturation of rocks. Layers that contain oil are less dense compared to those rocks that contain liquid. offbank.ru

The specificity of electrical exploration lies in the fact that this technique uses the difference in electrical conductivity of various minerals. In particular, the layers bearing oil fields are characterized by very low rates.

Magnetic exploration is based on the heterogeneity of magnetic permeability that accompanies interlayers that are not the same in deposits.

Types of hydrogeochemical methods

The modern industry is based on several technologies:

• hydrochemical method,
• luminescent-bitumonological photography,
• gas photography,
• radioactive photography. https://www.site/

Hydrochemical method allows to analyze the chemical features of groundwater, to recognize the biological components and gases dissolved in them.

Luminescent-bitumonological research is based on the fact that significant amounts of bitumen accumulate in the rock directly above the oil field. website

As a result of gas photography, researchers can detect hydrocarbon gases in samples from groundwater and rocks. The latter dissipate in the original oil location zone.

Radioactive imaging has a specific goal - to find an area with a low radiation field that usually accompanies oil deposits.

Technologies of additional confirmation

To delineate the boundaries of deposits, they resort to drilling wells. This technology allows not only to verify the estimated scale of occurrence - as a result, it is possible to identify the intensity (saturation) of the reservoirs.

Now electric logging is also widely used - this technique is effective when searching for sources of fossil fuels. A special device is placed in a pre-formed opening that reads electrical properties studied layers. offbank.ru

Practical study of oil fields

The search phase, as a rule, takes place in 3 stages:

1. Local geological and geophysical research. As a result, approximate boundaries of occurrence are determined, potential reserves are analyzed. At this stage, the developers set the areas that need to be emptied first.
2. Site preparation for drilling. Here it is necessary to provide a thorough and comprehensive oil-bearing location.
3. Definition of deposits. Openings are being drawn up, on which production will be based in the future. www.site

Most often, wells, equipped during the search, have a vertical orientation. But thanks to modern technical solutions it became possible to use more convenient inclined openings created at a wide range of angles.

After the exact presence of the deposit is established, the stage of its development is started, which is accompanied by the destruction of rocks. The impact can be rotational and shock. The first technology is reduced to the removal of particles crushed during drilling to the surface by letting the working fluid into the well. The impact method of rock destruction provides for a powerful mechanical effect, here the fragments are removed with the help of water. website

The speed of exploration depends on the quality and novelty of the equipment available, the type of base rock and the professionalism of the explorers. Only 30-50 wells may be needed to service one production, but it is not uncommon for their number to be in the thousands.

It is important to fully coordinate the circulation of the liquid, for this purpose special layouts of openings are developed, all aspects of their functioning are controlled. The whole complex of works described above is the heart of the process - the search and development of an oil field. offbank.ru

Overview of current trends

The last decade is characterized by high rates of exploration and development of oil fields. Now more than 1% of the planet's surface has been studied at a depth of 2-3 km. Marine deposits are also intensively developed.

One of the main trends in the industry is the minimum negative impact to the environment natural environment. In this connection, researchers are required to accurate calculations, allowing to make as few wells as possible during the search for oil.

Approximately 65 states are currently actively engaged in the identification and production of industrial oil. The richest in this respect are the following countries:

• Saudi Arabia,
• Russia,
• Libya,
• Venezuela,
• Canada,
• Iraq,
• Iran. https://www.site/

Not much inferior to them:

• Algeria,
• Qatar,
• Mexico,
• Nigeria,
• Argentina,
• India.

There are more than 10 thousand combustible hydrocarbon deposits on Earth, and a significant part of them are located on the territory Russian Federation. website

works apply geological, geophysical, methods, as well as drilling and exploration of wells.

Geological methods. Conducting a geological survey precedes all other types of prospecting work. To do this, geologists travel to the area under study and carry out so-called field work. In the course of them, they study the rock layers that come to the day surface, their composition and angles of inclination. To analyze bedrocks covered by modern sediments, pits are dug (vertical, less often inclined, shallow mine workings, usually with a rectangular cross-sectional area, passed from the surface) up to 3 m deep. And in order to get an idea of ​​deeper rocks, mapping wells up to 600 m deep are drilled.

Upon returning home, cameral work is performed, i.e. processing of materials collected during the previous stage. The result of office work is a geological map and geological sections of the area.

A geological map is a projection of rock outcrops onto the day surface. The anticline (the bend of the reservoir, directed upwards) on the geological map looks like an oval spot, in the center of which there are older rocks, and on the periphery - younger ones.

However, no matter how carefully the geological survey is carried out, it makes it possible to judge the structure of only the upper part of the rocks. To "probe" deep bowels use geophysical methods. Geophysical methods. Geophysical methods include seismic, electrical and magnetic prospecting.

Seismic exploration (Fig. 3.6) is based on the use of the patterns of propagation in the earth's crust of artificially created elastic waves.

Rice. 3.6.

Waves are created in one of the following ways:

• explosion of special charges in wells up to 30 m deep;
• vibrators;
• converters of explosive energy into mechanical.

The speed of propagation of seismic waves in rocks of different density is not the same: the denser the rock, the faster the waves penetrate through it. At the interface between two media with different densities, elastic vibrations are partially reflected, returning to the surface of the earth, and partially refracted, continue their movement deep into the bowels to a new interface. Reflected seismic waves are captured by geophones. Deciphering then the resulting oscillation graphs.

Electrical exploration is based on the different electrical conductivity of rocks. So, granites, limestones, sandstones, saturated with salty mineralized water, conduct electricity well, and clays, sandstones, saturated with oil, have very low electrical conductivity.

circuit diagram electrical exploration from the earth's surface is shown in fig. 3.7. An electric current is passed through metal rods and through the soil, and with the help of rods and special equipment, an artificially created electric field is investigated. Based on the measurements performed, the electrical resistance of rocks is determined. High electrical resistance is an indirect sign of the presence of oil or gas.

Rice. 3.7.

Gravity exploration is based on the dependence of gravity on the Earth's surface on the density of rocks. Rocks saturated with oil or gas have a lower density than the same rocks containing water. The task of gravity exploration is to identify places with abnormally low gravity.

Magnetic prospecting is based on different magnetic permeability of rocks. Our planet is a huge magnet with a magnetic field around it. Depending on the composition of rocks, the presence of oil and gas, this magnetic field is distorted to varying degrees. Often, magnetometers are installed on aircraft that fly over the area under study at a certain height. Aeromagnetic survey makes it possible to detect anticlines at a depth of up to 7 km, even if their height is no more than 200–300 m.

Geological and geophysical methods mainly reveal the structure of the sedimentary rock mass and possible traps for oil and gas. However, the presence of a trap does not mean the presence of an oil or gas deposit. Hydrogeochemical methods of studying the subsoil help to identify from the total number of discovered structures those that are most promising for oil and gas without drilling wells.

hydrogeochemical methods. Hydrochemical surveys include gas, luminescent-bitumonological, radioactive surveys and the hydrochemical method.

Gas survey consists in determining the presence of hydrocarbon gases in rock and groundwater samples taken from a depth of 2 to 50 meters. Around any oil and gas deposit, a halo of hydrocarbon gas dispersion is formed due to their filtration and diffusion through the pores and cracks of the rocks. With the help of gas analyzers with a sensitivity of 10 -5 10 -6%, an increased content of hydrocarbon gases is recorded in samples taken directly above the deposit. The disadvantage of the method is that the anomaly can be displaced relative to the deposit (due to the inclined occurrence of the overburden) or be associated with non-commercial deposits.

The use of luminescent-bitumonological surveys is based on the fact that the bitumen content in the rock is increased over oil deposits, on the one hand, and on the phenomenon of bitumen luminescence in ultraviolet light, on the other. By the nature of the glow, the selected rock samples make a conclusion about the presence of oil in the proposed deposit.

It is known that in any place of our planet there is a so-called radiation background, due to the presence of radioactive transuranium elements in its depths, as well as the influence of cosmic radiation. Experts managed to establish that the background radiation over oil and gas deposits is lowered. Radioactive survey is carried out in order to detect the indicated anomalies of the radiation background. The disadvantage of the method is that radioactive anomalies in the near-surface layers can be caused by a number of other natural causes. Therefore, this method is still of limited use.