Icebreaker Alexander Sannikov technical specifications. Icebreaker "Alexander Sannikov" - heading for the Arctic

Among them are new fracturing fluids, surfactants, hydrophobic agents and additives.

TagraS-RemService presented new technological solutions for hydraulic fracturing (HF) in difficult geological and technical conditions.

The company started using a new low-viscosity fracturing fluid with good sand-carrying properties. Usage this product allows:

1. Evenly place the proppant (proppant) along the height and length of the productive formation.

2. Control the growth of the fracture in height (carrying out hydraulic fracturing in reservoirs with weak barriers to water)

3. Reduce damage to the proppant pack after complete destruction of the gel (maintain fracture conductivity).

TagraS-RemService is working on laboratory testing of a new fixing material - modified sand. This product helps to reduce the movement of water along the hydraulic fracture, in particular, during the hydraulic fracturing operation on a high water cut well stock. Sand has hydrophobic properties, is evenly distributed over the entire height of the fracture and makes it possible to reduce the viscosity of the fracturing fluid.

The new technology of combined acid-proppant hydraulic fracturing based on gelled acid with surface-active substances (surfactants) reduces the process of development and well recovery, as well as reduces the risks of forced shutdown of the process. The use of new chemicals prevents the polymer from entering the reservoir. At the same time, the amount of fluid injected into the reservoir is reduced due to the fact that the injection cycle of an aqueous polysaccharide gel with proppant is eliminated.

TagraS-RemService is also mastering the technology of hydro-sand-jet perforation with further hydraulic fracturing. The main advantage of the new technical solution is the possibility of targeted stimulation of the formation without cutting off other perforation intervals, i.e. preliminary creation of a crack during hydrosandblast perforation. Operations can also be performed on wells with low quality cement stone behind the casing. This technology allows for multi-zone hydraulic fracturing in wells with horizontal completion.

In order to control the viscosity of the hydraulic fracturing fluid "on the fly" depending on the proppant fraction and concentration, it is proposed to use a new anti-sedimentation agent, which allows:

1. Evenly distribute the proppant along the fracture vertical.

2. Increase the sand-carrying capacity of the fracturing fluid.

3. Reduce the loading of the gelling agent.

TagraS-RemService recently presented these developments at the Oil. Gas. Petrochemistry” within the framework of the Tatarstan Petrochemical Forum. President of Tatarstan Rustam Minnikhanov got acquainted with the stand of the company.

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Hydraulic fracturing consists of three principal operations:

1. creation of artificial cracks in the reservoir (or expansion of natural ones);

2. injection of fluid with fracture filler through the tubing into the near-wellbore zone;

3. forcing fluid with filler into cracks to fix them.

These operations use three liquid categories:

• fracturing fluid,
• sand carrier
• selling liquid.

Work agents must meet the following requirements:

1. Should not reduce the permeability of the CCD. At the same time, depending on the category of the well (producing; injection; producing, converted to water injection), working fluids of different nature are used.

2. The contact of working fluids with the EZS rock or reservoir fluids should not cause any negative physical and chemical reactions, except for the cases of using special working agents with controlled and directed action.

3. Should not contain a significant amount of foreign mechanical impurities (i.e. their content is regulated for each working agent).

4. When using special working agents, for example, an oil-acid emulsion, the products of chemical reactions must be completely soluble in the production of the formation and not reduce the permeability of the near-wellbore zone.

5. The viscosity of the working fluids used must be stable and have low temperature solidification in winter time(otherwise, the hydraulic fracturing process should be carried out using heating).

6. Must be readily available, non-scarce and inexpensive.

Hydraulic fracturing technology :

• Well preparation- a study for inflow or injectivity, which provides data for the evaluation of fracture pressure, fracture fluid volume and other characteristics.
• Well flushing- the well is flushed with a flushing fluid with the addition of certain chemicals to it. If necessary, carry out decompression treatment, torpedoing or acid treatment. In this case, it is recommended to use tubing with a diameter of 3-4 "(pipes of a smaller diameter are undesirable, because friction losses are high).
• Fracture fluid injection- the pressure necessary for rock rupture is created for the formation of new and disclosure of cracks that existed in the CCD. Depending on the properties of the CCD and other parameters, either filterable or slightly filterable liquids are used.

Fracture fluids:

in production wells

degassed oil;

thickened oil, oil-oil mixture;

Hydrophobic oil-acid emulsion;

Hydrophobic water-oil emulsion;

Acid-kerosene emulsion, etc.;

in injection wells Oh

clean water;

Aqueous solutions of hydrochloric acid;

Thickened water (starch, polyacrylamide - PAA, sulfite-alcohol stillage - PRS, carboxymethylcellulose - CMC);

Thickened hydrochloric acid (a mixture of concentrated hydrochloric acid with PRS), etc.

When choosing a fracturing fluid, it is necessary to take into account and prevent clay swelling by introducing chemical reagents into it that stabilize clay particles when wetted (clay hydrophobization).

As already noted, the burst pressure is not a constant value and depends on a number of factors.

Increasing the bottomhole pressure and achieving the fracture pressure value is possible when the injection rate is ahead of the rate of fluid absorption by the formation. In low-permeability formations, fracturing pressure can be achieved by using low-viscosity fluids as the fracturing fluid at a limited injection rate. If the rocks are sufficiently well permeable, then when using low-viscosity injection fluids, a high injection rate is required; with limited pumping rate it is necessary to use higher viscosity fracturing fluids. If the CCD is a high permeability reservoir, then high injection rates and high viscosity fluids should be used. In this case, the thickness of the productive horizon (interlayer), which determines the injectivity of the well, should also be taken into account.

important technological issue is to determine the moment of crack formation and its signs. The moment of formation of a crack in a monolithic reservoir is characterized by a break in the dependence "volumetric flow rate of injection fluid - injection pressure" and a significant decrease in injection pressure. The opening of fractures that already existed in the wellbore zone is characterized by a smooth change in the “flow rate - pressure” dependence, but there is no decrease in injection pressure. In both cases, a sign of fracture opening is an increase in the well injectivity.

• Injection of sand-carrying fluid. Sand or any other material injected into the fracture serves as a fracture filler, being a framework inside it and preventing the fracture from closing after the pressure is removed (reduced). The sand carrier fluid performs a transport function. The main requirements for a sand-carrying fluid are high sand-holding capacity and low filterability.

These requirements are dictated by the conditions for effective filling of cracks with a filler and the exclusion of possible settling of the filler in individual elements. transport system(mouth, tubing, bottomhole), as well as premature loss of mobility by the filler in the fracture itself. Low filterability prevents filtration of the sand-carrying fluid into the walls of the fracture, maintaining a constant concentration of filler in the fracture and preventing plugging of the crack by the filler at its beginning. Otherwise, the concentration of the filler at the beginning of the crack increases due to the filtration of the sand-carrying fluid into the walls of the crack, and the transfer of the filler in the crack becomes impossible.

As sand-carrying fluids in production wells, viscous fluids or oils are used, preferably with structural properties; oil and oil mixtures; hydrophobic water-oil emulsions; thickened hydrochloric acid, etc. In injection wells, PRS solutions are used as sand-carrying fluids; thickened hydrochloric acid; hydrophilic oil-water emulsions; starch-alkaline solutions; neutralized black contact, etc.

To reduce friction losses during the movement of these fluids with filler along the tubing, special additives (depressants) are used - solutions on soap base; high molecular weight polymers, and the like.

• Displacement fluid injection - squeezing the sand-carrying fluid to the bottom and pushing it into the cracks. In order to prevent the formation of plugs from the filler, the following condition must be observed:

where is the speed of movement of the sand-carrying fluid in the tubing string, m/s;

Viscosity of the sand-carrying liquid, mPa s.

As a rule, liquids with a minimum viscosity are used as displacement fluids. Production wells often use their own degassed oil (if necessary, it is diluted with kerosene or diesel fuel); Injection wells use water, usually commercial.

As a crack filler can be used:

Quartz sorted sand with a grain diameter of 0.5 +1.2 mm, which has a density of about 2600 kg/m3. Since the density of sand is significantly greater than the density of the sand-carrying liquid, the sand can settle, which predetermines high speeds downloads;

Glass balls;

Grains of agglomerated bauxite;

polymer balls;

Special filler - proppant.

Basic requirements for the filler:

High compressive strength (collapse);

Geometrically correct spherical shape.

It is quite obvious that the filler must be inert with respect to the production of the reservoir and not change its properties for a long time. It has been practically established that the concentration of the filler varies from 200 to 300 kg per 1 m3 of the sand-carrying liquid.

• After the filler is injected into the fractures, the well left under pressure. The dwell time should be sufficient for the system (CCD) to pass from an unstable to a stable state, in which the filler will be firmly fixed in the crack. Otherwise, in the process of stimulation of the inflow, development and operation of the well, the filler is carried out of the fractures into the well. If at the same time the well is operated by pumping, the removal of the filler leads to the failure of the submersible installation, not to mention the formation of plugs from the filler at the bottom. The above is extremely important. technological factor, the neglect of which sharply reduces the efficiency of hydraulic fracturing up to a negative result.
• influx call, development of a well and its hydrodynamic study. Conducting a hydrodynamic study is an obligatory element of the technology, because its results serve as a criterion for the technological efficiency of the process.

circuit diagram well equipment for hydraulic fracturing is presented on rice. 5.5. During hydraulic fracturing, the tubing string must be packed and anchored.

Important issues during hydraulic fracturing are determining the location, spatial orientation and size of cracks. Such definitions should be mandatory when fracturing in new regions, because. allow to develop best technology process. The listed tasks are solved on the basis of the method of observing the change in the intensity of gamma radiation from a crack into which a portion of the filler activated by a radioactive isotope, for example, cobalt, zirconium, iron, is injected. Essence this method consists in adding a certain portion of the activated filler to the clean filler and conducting gamma-ray logging immediately after the formation of fractures and injection of a portion of the activated filler into the cracks; comparing these results of gamma-ray logging, they judge the number, location, spatial orientation and size of the fractures formed. These studies are carried out by specialized field geophysical organizations.

Rice. 5.5. Schematic diagram of well equipment for hydraulic fracturing:

1 - productive formation; 2 - crack; 3 - shank; 4 - packer; 5 - anchor; 6 - casing string; 7 - tubing string; 8 - wellhead equipment; 9 - fracturing fluid; 10 - sand carrier liquid; 11 - squeezing liquid; 12 - manometer.

Problems of hydraulic fracturing application. ASS where next to the reservoir are layers containing water. It could be aquifers if bottom water. In addition, there may be formations adjacent to the treated formation that are waterflooded.

Vertical cracks formed during hydraulic fracturing in similar cases create a hydrodynamic connection of the well with the aquifer. In most cases, the aquifer has a higher permeability compared to the reservoir where the hydraulic fracturing is carried out. That is why hydraulic fracturing can lead to complete flooding of wells. In old fields, many wells are in disrepair. Hydraulic fracturing under such conditions leads to rupture of the production string. Theoretically, in such wells, a packer is used to protect the string, but due to dents on the string and corrosion, the packer does not fulfill its role in such wells. In addition, due to hydraulic fracturing, cement stone can be destroyed.

During hydraulic fracturing, fractures are created in interlayers with different permeability, but very often it is easier to break a high-permeability interlayer than a low-permeability one. In an interlayer with a higher permeability, the fracture may be longer. With this option, after hydraulic fracturing, the well's oil production rate increases, but the water cut increases if the well was watered. That is why, before and after hydraulic fracturing, it is necessary to analyze the produced water in order to find out where the water came from in the well.

During hydraulic fracturing, as with any stimulation methods, the question always arises of compensating for large production by injection.

Russia expects increased sanctions pressure. UK and US are actively looking for new grounds for discrimination Russian business. However, the results of the latest wave of sanctions policy, which began in 2014, are far from unambiguous. Even independent studies show that the Russian fuel and energy complex has not suffered much from the restrictions, moreover, they have spurred the development of industry in Russia. According to industry experts, the possible strengthening of anti-Russian sanctions will also not become critical for the Russian fuel and energy complex, but only if the government and energy companies mobilize forces in time to create a domestic engineering industry that produces equipment for mining hard-to-recover reserves oil (TRIZ).

Russia must learn how to extract TRIZ

The day before, the Energy Center of the SKOLKOVO Business School presented the results of its study “ Prospects for Russian oil production: life under sanctions”, which analyzed the impact of the sanctions imposed in the US and the EU on the Russian oil sector, in particular on the commissioning of new traditional fields in Russia, the development of offshore projects, and the extraction of Bazhenov oil. The authors of the study also made a scenario forecast of Russian oil production until 2030.

The document notes that on the horizon until 2020, despite all the restrictions, Russia has the potential to further increase production volumes at the expense of already prepared fields. This short-term upside, however, may be limited by arrangements with OPEC. In the medium term until 2025, even in the event of severe restrictions on access to technology and a low oil price, production volumes will not suffer catastrophically. Wherein main reason The decline in production during this period may be not so much the lack of access to Western technologies for the implementation of new projects, but the lack of technological capabilities to intensify production at existing fields.

This study has shown that hydraulic fracturing is the most critical technology for maintaining Russian oil production, as it is able to maintain production at existing fields.

The use of MSHF (multi-stage hydraulic fracturing) promises to increase production in promising unconventional fields.

The authors of the study emphasize that under the current conditions, it is the development own technologies Hydraulic fracturing and multi-stage hydraulic fracturing, production of domestic hydraulic fracturing and multi-stage hydraulic fracturing fleets and training of personnel should become a technological priority for industry companies and regulators. However, so far, work in this direction is being carried out at a clearly insufficient pace. As the expert of the Energy Center of the SKOLKOVO Business School Ekaterina Grushevenko noted in her report, in the period from 2015 to August 2017, not a single hydraulic fracturing fleet was produced. Rotary-controlled systems, according to the website of the Scientific and Technical Center of Gazprom Neft PJSC, at the end of 2016 were in the testing stage. The expert stressed that already now two thirds of oil reserves are in hard-to-find reserves.

Until 2020, production cuts are not expected

Director of the Energy Center of the SKOLKOVO Business School Tatiana Mitrova in her speech at the presentation of this study, she noted that the first sanctions against Russia and Russian energy companies were introduced in 2014, but no special studies on their impact on the oil industry have been published.

“We didn't know what result we would get. The first hypothesis suggested that the consequences would be very severe,” Mitrova said. However, the results showed a slightly different picture of the impact of sanctions.

"Currently, no serious consequences sanctions in the operating activities of companies are not felt. Indeed, the extraction last years grew despite low prices and sanctions. The oil industry has reported success. But the positive current situation should not be misleading, the analysis of the complex of sanctions itself indicates their very broad interpretation, this is the main threat of sanctions pressure,” the expert said.

According to her, until 2020, according to the simulation results, no reduction in production is expected, since the main projects have already been financed.

“Starting from 2020, negative trends will become more and more noticeable and may lead to a decrease in oil production in Russia by 5% by 2025 and by 10% by 2030 from current production levels. A decrease in production in such proportions, of course, is not catastrophic for Russian economy, but nonetheless quite sensitive,” Mitrova said.

She stressed that sanctions are a long story, and in order for the Russian oil industry adapted to them, additional efforts are needed by the state and companies to develop their own technologies and production necessary equipment.

“There is a huge part of oil production that directly depends on hydraulic fracturing technology. Precisely the presence this equipment has the greatest impact on the volume of oil production in the country. But the development and implementation of the production of this technology is more of a task Russian government and industry,” the director of the Energy Center explained.

A new industry is required

Head of the "Gas and Arctic" direction of the SKOLKOVO Business School Roman Samsonov in his speech, he noted that, according to his personal observations, in Russia, only against the backdrop of sanctions, one can observe progress in the development and production of its own high-tech equipment.

“The situation with the production of high-tech equipment is difficult, but you can learn how to manage it. Actually we are talking on the creation of an entire multifunctional sub-sector of oil and gas engineering,” said Samsonov.

According to the participants of the study “Prospects for Russian oil production: life under sanctions”, such big task on the creation of a new sub-sector of heavy engineering in Soviet times was solved only thanks to state directives. In the conditions of modern market economy, in which the Russian Federation is currently developing, the mechanisms for the implementation of this task have not yet been worked out.

However, this is only in Russia. Looking at experience Western countries, which successfully overcome all difficulties for the production of TRIZ, it becomes clear that such a method has long been found. This is most clearly seen in the example of the US shale industry, which was actively lending even during the period low prices which helped her survive. Obviously, such a tolerant attitude of banks to this sector of oil production could not do without state participation. Now the grateful shale players are helping the US authorities to restrain OPEC and other oil producers, actively influencing the global oil and gas market.

Ekaterina Deinego

Recently, hydraulic fracturing (HF) has been increasingly used in oil production. HF is one of best practices impact on the bottomhole zone of wells. The very first experience of hydraulic fracturing in the Kogalym region was carried out in 1989 at the Povkhovskoye field. Since then, a lot of time has passed, various technologies have been introduced hydraulic fracturing, and this process has become an integral part of the operation of all fields of the enterprise. If earlier the main task of hydraulic fracturing was to restore the natural productivity of the reservoir, degraded during drilling and operation of wells, now the priority is to increase oil recovery from reservoirs at fields that are at a late stage of development, both due to the involvement in the development of poorly drained zones and intervals in objects with a high degree development of reserves, and involvement in the development of low-permeability, highly dissected objects. The two most important developments in oil production over the past 15 years are hydraulic fracturing and horizontal well drilling. This combination has very high potential. Horizontal wells can be drilled either perpendicular or along the fracture azimuth. Virtually no technology oil and gas industry does not give such a high economic return. Employees of the Tevlinsko-Russkinskoye field were convinced of this by testing the interval fracturing method at well 1744G. Yury Miklin, Leading Engineer of the EOR Department, told us about the successful experience.

In the era high prices For energy carriers, producing companies strive to extract the maximum from their assets, producing as many hydrocarbons as economically justified, - says Yuri, - for this purpose, extended reservoir intervals are often involved in development through horizontal wells. The results of traditional hydraulic fracturing in such wells may be unsatisfactory for economic and technological reasons. Method of interval or, as they say, multi-interval hydraulic fracturing, is able to provide more efficient recovery of oil reserves by increasing the contact area of ​​the fracture with the formation and creating highly conductive paths for oil movement. Degraded reservoir properties are forcing oil companies to look for more and more cost-effective ways to build a well to further stimulate the reservoirs of interest using the latest advances in science and technology. Realizing this, companies are striving to reduce the time and, consequently, the cost of additional tripping operations and crew work. overhaul wells with the help of special equipment, which becomes integral part wells.

One way out is to complete the well with a horizontal liner with circulation valves on the assembly, which serve to pump the mixture of liquid with proppanite. This assembly includes swellable packers designed to secure and stabilize the liner in an open hole.

Process hydraulic fracturing formations consists in creating artificial and expanding existing cracks in the rocks of the bottomhole zone under the influence of increased pressures of the fluid injected into the well. This entire system of fractures connects the well with the productive parts of the formation remote from the bottomhole. To prevent cracks from closing, coarse-grained sand is introduced into them, which is added to the fluid injected into the well. The length of cracks can reach several tens of meters.

Here it should be taken into account that the distance between the places of installation of circulation valves and, accordingly, the places of initiation of fractures in a horizontal wellbore will affect the productivity of each section, - Yury notes, - that is, it is required to choose the optimal distance between fractures, based on the geometry of the designed fractures. We must protect ourselves as much as possible from crossing fractures in the reservoir, which can cause complications during hydraulic fracturing. Ideally, the maximum flow rate is possible with a distance between fractures equal to the drainage radius. This condition is not feasible, given the design of well 1744G, so the location of the fractures had to be chosen with the maximum possible distance from each other.

Given the sloping formations, horizontal wells are the best way to increase the area of ​​contact with the productive formation. Holding hydraulic fracturing according to the "Zone Select" technology is as follows: first, hydraulic fracturing the furthest interval through the arrangement in which the circulation valve is already open. After that, a ball is launched from the surface into the tubing string (tubing), together with the displacement fluid, which, reaching the bottom of the well, first opens the second circulation valve to treat the next section, and then sits in a special seat, cutting off the treated interval. With two treatment intervals, one ball is used. In proportion to the increase in the number of processing intervals, the number of balls also increases. Moreover, each next ball should be of a larger diameter than the previous one. Balls are made of aluminum, and this is important. After stimulating the required number of intervals and pumping the calculated amount of a mixture of fluid and sand, the hydraulic fracturing fleet leaves the well. A fleet of coiled tubing (coiled tubing) is installed on the well, which flushes, mills balls and develops the well with the determination of the inflow profile and production capabilities of the well. Development is carried out with nitrogen - this is the most promising direction to reduce downhole pressure. TPE "Kogalymneftegaz" used this technology to treat two intervals of well 1744G of the Tevlinsko-Russkinskoye field. Compared to neighboring horizontal and directional wells after hydraulic fracturing using standard technology, this well achieved higher technological performance. The initial oil flow rate at well 1744G was about 140 tons per day.

Finally, I would like to note that it is the large-scale application hydraulic fracturing allows to stop the decline in oil production at the fields of TPE "Kogalymneftegaz" and increases the production of reserves from medium and low-productive reservoirs. The advantages of performing interval hydraulic fracturing in horizontal wells using the “Zone Select” technology is not only an increase in the effective area of ​​contact between the reservoir and the well draining the reservoir, but also overcoming damage to the bottomhole zone of the wellbore after drilling, as well as bringing into development poorly drained areas with low porosity and permeability. properties. This indicates that horizontal wells using interval hydraulic fracturing are more efficient and cost-effective.

Director of ICT SB RAS Sergei Grigorievich Cherny.

Why hydraulic fracturing (HF) is needed, why it needs to be simulated, what is an advanced model and who is interested in it - these and other questions are answered by the director of the Institute of Computational Technologies of the Siberian Branch of the Russian Academy of Sciences, Doctor of Physical and Mathematical Sciences Sergey Grigoryevich Cherny.

1. Why hydraulic fracturing is needed

Hydraulic fracturing was invented for the development of mineral deposits and the construction of underground structures in difficult geological and physical conditions - when methods of controlled destruction and unloading of rock masses are needed, the creation of drainage systems in them, insulating screens, and so on. Hydraulic fracturing occupies a special place among the methods of intensifying the operation of oil and gas production wells and increasing the injectivity of injection wells. In 2015-2017, 14-15 thousand hydraulic fracturing operations per year were carried out in Russia, and about 50 thousand in the USA.

The hydraulic fracturing method consists in creating a highly conductive fracture in an untouched rock mass to ensure the flow of gas, oil, their mixture, condensate, etc. to the bottom of the well. acids. The injection pressure is higher than the fracture pressure, so a fracture is formed. To fix it in the open state, either a proppant is used, which weds the fracture, or an acid, which corrodes the walls of the created fracture. The name proppant comes from the English abbreviation "propping agent" - proppant. In this capacity, for example, quartz sand or special ceramic balls are used, which are stronger and larger, and, therefore, more permeable.

2. Why fracturing modeling is needed

Creation of hydraulic fracturing technology requires modeling of its process. This makes it possible to predict the fracture geometry and optimize the entire hydraulic fracturing technology. In particular, it is very important to ensure correct form cracks in the initial section of its propagation in the vicinity of the well. It is necessary that it does not have sharp bends, which can lead to plugs that clog the channel for pumping out oil or gas produced. A natural question arises: where to get the geophysical data on the reservoir necessary for the model, such as permeability, porosity, compressibility, stress state, and others?

This question arose long before the development of hydraulic fracturing technology, and science offered many methods for determining various task parameters. This includes the analysis of cores (rock samples obtained during drilling), and multiple pressure and strain sensors installed in various parts of the well, and seismic survey methods, in which the boundaries of various materials in the rock are determined by the time of passage of elastic waves induced from the surface and their parameters, and even measurements of natural radioactivity, which can show, for example, the location of clay interlayers.

Geophysicists have proven technologies to determine the principal stresses in a pristine rock mass, including those based on field drilling and geophysical measurements. The mini-fracturing technology is also used, in which, according to the parameters obtained in the process of creating a small fracture, models are calibrated that will predict the behavior of a larger fracture. Of course, none of the approaches can give a complete picture, therefore, methods for obtaining information about the reservoir are constantly being improved, including at our institute. For example, we have shown that the fracturing parameters of the rock surrounding the well can be determined by solving inverse problems based on mud filtration models and measured well pressure dependences. We also determine the structure and parameters of the near-wellbore area based on the results of well logging, solving the inverse problem based on Maxwell's equations.

3. How long has hydraulic fracturing modeling been carried out?

A relatively long time ago, since the 1950s, almost immediately after hydraulic fracturing began to be used as a method to increase well productivity. At the same time, in 1955, one of the first hydraulic fracturing models was proposed - the Khristianovich-Zheltov model, which received further development in the work of Girtsma and de Klerk and known worldwide as the Khristianovich-Girtsma-de Klerk (KGD) model. A little later, two more well-known, widely used and currently used models were created: Perkins-Kern-Nordgren (PKN) and the model of a plane-radial crack. These three models represent, respectively, three basic geometric concepts in a set of planar one-dimensional models:

• rectilinear crack propagation from a linear source of infinite height;
• rectilinear crack propagation from a linear source of finite height;
• radial symmetric crack propagation from a point source.

The three basic concepts and their modifications adequately describe hydraulic fracturing for typical well orientations in traditional oil and gas fields, involving vertical or deviated drilling and one hydraulic fracture per well. These models have not lost their relevance and, due to their speed, are used in modern hydraulic fracturing simulators, both to obtain primary information about the fracture and to optimize hydraulic fracturing parameters.

However, at present, due to the depletion of traditional, easily recoverable reserves, an increasing place in the world is occupied by the development of unconventional deposits, which are characterized by more complex structure oil and gas reservoirs. Distinctive features of such reservoirs are low (tight sand) and ultra-low (shale gas and oil) or vice versa extremely high (sandstone with heavy oil) reservoir permeability, the presence of an extensive system of fractures that may contain one or more families oriented in different directions and crossing each other. Very often, the development of such unconventional fields becomes economically unprofitable without such stimulation of production as hydraulic fracturing. At the same time, traditional hydraulic fracturing models do not adequately describe these processes, and new, more refined (modern, advanced, improved) models are required.

4. Is ICT SB RAS able to solve the problem of hydraulic fracturing modeling for unconventional fields

Hydraulic fracturing is a complex technology, and the development of a model of the entire process is not within the power of one institute, therefore, groups of scientists around the world are concentrating on various parts of this technology. IWT has extensive experience in modeling the initial stage of hydraulic fracture propagation: from its formation to reaching several meters in size. At this stage, in contrast to a developed crack, the size of which reaches hundreds of meters, the curvature is strongly noticeable and strongly affects, which must be taken into account.

Therefore, we are developing the direction of improving the models in terms of taking into account the three-dimensionality of the propagation process in them. For a realistic description of the crack front propagation in an arbitrary three-dimensional case, it is necessary to apply the three-dimensional criterion for finding the increment of the crack front and choosing the direction of its propagation, taking into account mixed loading in all three stress modes. Among existing works, devoted to three-dimensional propagation models, the crack front deviation is determined only by the second mode. They use two-dimensional flat criteria. We have constructed and verified a new fully three-dimensional numerical model of fracture propagation from a cavity under the pressure of an injected liquid of complex rheology with a three-dimensional propagation criterion. It made it possible to describe the evolution of a crack from the moment of its formation to the exit to the main direction, taking into account its curvature.

One more distinctive feature This model is the simultaneous consideration of the well itself and the variable load caused by the flow of fluid in a fracture propagating from the well. Typically, in 3D fracture propagation modeling work, the well is not present in the model. In the best case, a variable load in the fracture is considered, caused by the injection of a Newtonian fluid into it from a point source.

It should also be noted that the technological development of unconventional reservoirs is accompanied by the design of new hydraulic fracturing fluids and various additives to them (fibers, flock, etc.), which significantly change the rheological behavior of these fluids. For example, the growing interest in tight and ultra-tight unconventional reservoirs with a high content of clay has led to the development of special compositions with high gas fractions and low water fractions. These fluids do not impair the filtration properties of the rock and do not cause its physical destruction during their injection.

In our monograph, published in 2016, we summarized the fracture models developed by ICT SB RAS. It collects results published in high-ranking journals included in the WoS and Scopus citation databases, such as Engineering Fracture Mechanics, International Journal of Fracture, and others.

5. Why you need a modified model

How the developed crack will be located is more or less known. There is a term preferred fracture plane - the plane of preferred crack propagation. If the stresses (forces) compressing the rock and their directions are known (it is also a problem to determine them, geophysicists are engaged in it), then this plane is not difficult to determine. Modern models and simulators focus on the fracture configuration in this plane. When a fracture is just emerging from a well, the position and direction are affected not only by stresses in the rock, but also by the well, the casing string, and perforations (holes in the rock), their shape, and size. And the direction of the crack at the beginning of the process does not always coincide with the plane in which the developed crack will lie. Inevitably, a crack curvature occurs, in which crack compression occurs. Such pinching not only can lead to proppant sticking, but also causes a strong pressure drop in the well. Now in simulators, this pressure drop is taken into account using an empirical coefficient - the skin factor, and not very successfully. Our model allows us to more accurately predict and describe this effect.

6. Can the modified hydraulic fracturing model be applied directly to the fields

Initially, IWT was not focused on the implementation of known models and the development of technologies, but concentrated on creating them. scientific foundations. However, such foundations also have a direct practical use. For example, at the beginning of the hydraulic fracturing process, more pressure is required to initiate a fracture than to maintain it. And it is not always easy to determine this pressure, but the amount and type of equipment required depends on it. Approximate analytical estimates, there were attempts to calculate, but the final solution to the problem was not found. We have developed a fracture initiation model, which predicts both the fracture pressure, the type of the formed fracture, and its orientation based on the configuration and stresses in the rock.

This model cannot be directly applied in the field. Calculation and setup takes some time. In addition, precise knowledge of stress directions, their values, and perforation directions is required. Usually this information is not available, since the accuracy of measurements is not always sufficient, due to the high cost, not all stresses in the rock are measured, the directions of the perforations cannot be accurately determined, since there are several kilometers from the place where the casing string is fixed to the perforations.

But the model can tell which well orientations are the most dangerous from the point of view of unsuccessful hydraulic fracturing, from the point of view of the formation of a longitudinal fracture (which is undesirable in multi-stage hydraulic fracturing), pressure intervals required to start hydraulic fracturing. For example, we conducted such a study commissioned by Schlumberger for a field in Oman, which is located at a depth of more than four kilometers and is highly compressed not only in the vertical but also in the horizontal direction, which is why there were fewer successful hydraulic fracturing attempts on it. half.

7. What is the future of hydraulic fracturing in the context of the “new oil”

The current state of traditional oil and gas reserves can be characterized by the word "depletion". More and more is being produced from unconventional, hard-to-recover reservoirs. Examples are the carriers of the so-called "shale oil" or, to use the correct term, "tight reservoir oils" in the US and Canada, or the Bazhenov formation in Russia. The latter, although it has huge reserves, is much more difficult to develop. The rock has many features not only in comparison with traditional collectors, but also with the “shales” popular on the American continent. Firstly, these are weak hundreds and tens of times, respectively, permeability and porosity. That is, it contains less oil, and it moves to the well worse. Oil from such rocks cannot be produced without the use of hydraulic fracturing.

Secondly, rocks of this type are characterized by strong layering and plasticity, or rather fluidity, high pore pressure, which complicates both hydraulic fracturing and its modeling. From the point of view of the latter, it is necessary to additionally take into account the anisotropy of stresses, material, plastic effects in describing the propagation of a fracture, and the nonlinearity of deformations when a fracture settles on the proppant. I would like to note that in addition to hydraulic fracturing itself, the development of this formation requires the solution of many scientific and technological problems, which are being worked on by scientists at Skolkovo and Moscow State University, in St. Petersburg and Novosibirsk.