The Bazhenov Formation: In Search of Big Shale Oil in Upper Salym

This article looks at the work performed by Salym Petroleum Development N.V. for the pilot development of the Bazhenov Formation. The research program has helped to identify key geological features of the Bazhenov Formation of the Upper Salym field, which have helped define the ways of drilling, completion, field development and hydrocarbon reserves estimation.

Introduction
Mainstream news has recently been reporting about the success of alternative energy and oil and gas production has significantly increased in the US due to the “shale gale”. This has had a knock on effect to many other organisations related to the power industry and they have reacted accordingly. Some people see this associated energy cost reduction as a threat, others see it as an opportunity to increase production, and others see this as a chance to gain energy independence.

The hunt for shale oil is a direct result of high energy demand, limited traditional resources bases, and the use of new technology able to reduce production costs. You can compare the cost of research and technology for shale oil deposits with space exploration, so it is no wonder that even the big IOCs are combining their efforts in order to share the burdens and risks. Even combined efforts are sometimes in vain however without due support from Governments.

Russia is one of the recognized world leaders in the production of oil and gas, but the depletion of traditional fields requires the establishment of a new resource base comparable in its size with the largest producing oil and gas provinces. Equivalent alternatives are the development of Arctic shelf, and indeed the Bazhenov Formation, which is prevalent almost right across western Siberia and is the world’s largest oil shale formation. The development of the Arctic shelf needs significant infrastructure development, and lies in regions with very harsh climatic conditions unsuitable for permanent human settlements. On the other hand, the Bazhenov formation occurs in areas with developed oil producing infrastructure, and indeed in the territory of producing fields. For Russia, its development is of great social importance, as the decline in oil and gas production in Western Siberia will affect the well-being of many Western Siberian cities and towns in which oil and gas companies are the major employers.

Because of these facts, the development of the Bazhenov is being discussed across multiple media platforms, including scientific, economic and political. When reviewing the reports, readers would quite rightly end up bewildered at the inconsistency of figures and estimates. Light oil estimates in the Bazhenov range from 600 million to 174 billion tons [1, 2]. As a comparison, the middle of this range is larger than the total initial geological reserves of light oil in all known oil and gas provinces of Russia.

Another distinctive feature associated with the Bazhenov Formation is an extremely low permeability ranging from a microdarcy (10-6) to a nanodarcy (10-9), and even to femtodarcy (10-15) [3]. At this level many publications reported natural flow of tens or even hundreds of cubic meters per day (without special well interventions) [4, 5, 38, and many others].

With such low permeability and real possibilities of creating drawdown it would not be feasible to cause any significant inflows in principle, say nothing of natural flow.

This lack of a clear understanding by geologists regarding the problems of the Bazhenov makes it very difficult for the RF Government to implement tax breaks for subsoil users willing to develop fields. The main reason is that the Bazhenov deposits behave unpredictably. In some instances, production rates are so high that the oil itself can be supplied to a central processing facility located dozens of kilometres from the wells due to the high formation pressure. In other cases, wells do not flow at all even after multiple and expensive well intervention operations. Indeed two wells can often be drilled very close to each other in similar geological conditions and produce completely different results. With this in mind, operators and investors looking to develop the Bazhenov face great risks and uncertainties.

Due to SPD’s research program, we have answered some of the key questions related to the geological features of the Bazhenov formation of the Upper Salym field. As a result, the company has a clear vision of what needs to be done to develop this formation, and a viable strategy for future operations.

Salym Project
Salym Petroleum Development N.V. (SPD) is a joint venture established in 1996 to develop the Salym group of oil fields in Western Siberia. This group includes West Salym, Vadelyp and Upper Salym fields located south of the Khanty-Mansi Autonomous Okrug. The SPD shareholders on a parity basis are Shell and Gazprom Neft. Full-scale development began in 2003, and in 2011, SPD hit peak production at 8.3 million tons per year through 600 wells. Currently, the company has over 820 wells, 15 which are water source wells. The main development targets are Lower Cretaceous deposits of Cherkashin (AC9-AC11) and Akhsk formations (BC8); and deposits of the Achimov Formation are also in pilot production.

The SPD approach is to blend the most advanced Russian experience of oil production and combine it with the latest technology from its shareholders and other leading world oil companies. As a result, SPD gets a unique product which sets the company apart from other oil companies around the world. The effectiveness of these approaches is backed up by numerous awards and recognition both in Russia and abroad in the field of oil production, health, safety and environment and health care [6, 7]. SPD is the first company both in Russia and among the first in Shell, to implemented a full-scale “Smart Fields” technology for the entire well stock and, together with its contractors, has achieved excellent results in well drilling (the record is 4.54 days), with the average time of well completion being 5.48 days, 100% recovery per one run for coring (78.93 m), an open hole logging time of 2 hours 55 minutes, among many other achievements [6].

Currently, SPD has launched two pilot projects aimed at changing attitudes to oil production techniques in Western Siberia: to enhance oil recovery by injecting chemicals into the formation and to start the pilot development of the Bazhenov Formation. This article focuses on the first phase of the Bazhenov pilot project aimed at resolving high priority geological tasks. Work started with exploration of the deep horizons and ended with a model of the Bazhenov Formation deposits of the Upper Salym field as the most promising for further development.

Supplementary Exploration of Salyms Deep Horizons
Between 1966 and 1993, 16 deep wells were drilled in the Salym group of fields to explore the Jurassic deposits. This section interval, represented by the Bazhenov, Abalak and Tyumen formations, was the subject of commingle testing; as a result, water-free oil was produced in most of the wells with flow rates not exceeding 10-15 m3/day. These were back in the days of big West Siberian oil, so low production rate formations were not studied properly. A minimum range of geophysical surveys, most of low quality, were conducted in the wells. In most cases, basic methods such as radioactive or sonic logging, which are very useful complex geological sections, were not even used. Core samples were taken in some wells, but it were then lost forever before SPD obtained its license. Almost all oil flows from the Jurassic horizons were produced within one license area – Upper Salym, and no studies to determine the affinity of the oil flows to certain intervals were conducted. Because of this, the exploration maturity of the Jurassic interval of the section is extremely low.

Between 2009 to 2011, in the Upper Salym field, SPD implemented a program of additional exploration of the Jurassic section. The company drilled three exploration wells, two of which were used to conduct various studies including mud logging, coring, standard and special open hole logging and production log (PLT) during the well testing. The aggregate of all these methods enables us to understand, with greater certainty, complex sections such as deposits of the upper and middle Jurassic in the southern part of the Khanty-Mansi Autonomous Okrug. The studies have shown that almost all oil flows are related to deposits of the Bazhenov Formation, and it was concluded that they are the most promising for the further development.

The Bazhenov formation is a very complex and unconventional development target for which there are no effective operational best practices. The oil deposits are not controlled by common geological features and do not contain any free waters, so in order to find a reservoir, with or without using well interventions, would require the elimination of most of the geological risks and uncertainties. Developing reliable models in the Bazhenov formation is a major challenge faced by geologists when planning cost effective field development.

Many scientific papers have been written about the Bazhenov Formation and, perhaps, it is the most studied geological formation in Western Siberia today. But the researchers have no consensus about its geological structure, especially when it comes to the location of pay zones. In order to navigate this variety of conflicting and often diametrically opposed concepts and points of view it is necessary to understand where the contradictions lie. This can be done by knowing the characteristics and conditions that shaped the views of the researchers.

SPD 2

The History and Current Status of Bazhenov Studies
Views and feelings of geologists and oilmen working at the Bazhenov were taken after events that happened in 1968 in Salym near the village of Gornopravdinsk (150 km from the Upper Salym Field). When deepening exploration well 12-R to 2860 m in the Jurassic horizon, an uncontrolled oil well blowout occurred, resulting in a rig fire. By visual accounts the production rate reached about seven hundred tons per day. By order of B. E. Scherbina, the First Secretary of the Communist Party Committee of the Tyumen Region, a prosecutor’s inspection was appointed to investigate the accident. The best professional geologists tried to prove that the incident was not caused by human error, but by natural factors. The blowout occurred in an area, where, in principle, it could not occur – while drilling in “standard shale”. But the actual reservoir pressure exceeded expectations by almost twice! The overlying and underlying sandstones of the Achimov and Tyumen formations, respectively, according to the most optimistic estimates, could only produce a maximum of 20-30 tons/day [9, 10, 11].

To determine the reason for the oil blowout, thanks to the insistence of A.V. Tyan, then head of the geological department of the Pravdinskaya Petroleum Exploration Expedition (PEE), and I.I. Nesterov, a Geology section head of ZapSibNIGNI, F.K. Salmanov, Chief of Pravdinskaya PEE, took the decision to drill a new exploratory well, 24-R, so that they could log and test every ten meters. In August 1969, this well penetrated the Achimov horizon. At this level, only minor oil flow was seen, but when the drill bit reached the middle of the Bazhenov Formation, to everyone’s surprise, natural flow of about 300-400 tons/day was produced! On this basis, August of 1969 can be considered a key starting point in the study of the Bazhenov Formation as a commercially oil-bearing formation. As a direct result, comprehensive studies began. Coring was very intensive in Western Siberian oil fields and was followed up by testing, with geological and research institutes beginning to analyse and process the incoming materials. Soon, oil-bearing capacity was discovered in the Studyonaya, Verkhne-Shapshinskaya, and Multanovskaya prospecting areas [9,10,11].

By 1974, pilot commercial development of the Salym test field had already begun. 72 wells were drilled on a trial plot of 10,035 hectares, of which 11 were dry, 25 were shut in with production of less than 1000 tons, and 19 wells exceeded 20,000 tons. Due to the oil-wet rock and specific reservoir characteristics, development was carried out solely with the natural reservoir flow with partial degassing [12].

These depressing statistics, ostensibly in the most promising area, ruined the bright expectations regarding potential oil production from the Bazhenov Formation. It stimulated great interest however which peaked in the 1980’s. There was a department in every major oil and gas geological research institute in the Soviet Union dedicated to the study of the Bazhenov Formation. The works of a number of leading institutes like ZapSibNIGNI, SibNIINP, IGiRGI, and others, prove the depth and scale of research works performed [3,13,14].

From 1985-1986, two reports on the evaluation of Bazhenov Formation deposits at the Salym field were finished, to be reviewed by the State Reserves Commission under the Council of Ministers of the USSR (USSR SC) [15,16]. So far however there is no accepted method, by the Russian Reserves Commission, for the calculation of oil reserves in the Bazhenov Formation, due mainly to lack of a clear view, is based on core samples, as to what is the reservoir. Core had been taken from 28 wells, with the total coring at the Bazhenov at 778.5 m, of which 325.4 m were recovered, i.e. 41.8% of the total penetration. The percentage of core recovery in wells ranged from 0.16% to 78.6% [15].

Because of these technical problems with coring, geologists had no way to accurately describe this cross section of the formation. Cores recovered to the surface were, as a rule, non-permeable rocks and, therefore had everyone guessing about the properties of the reservoir. The situation was aggravated by the fact that during the withdrawal of the core to the surface, a sharp decrease in vertical stress occurred, and with some cores being under abnormally high pore pressure (AHPP), they exploded and turned into powder (obviously, such behaviour is typical for low-permeability rock) or stratified. So at the moment, we have more than a dozen, often opposed geological models of the structure of the Bazhenov Formation.

These summaries can be found in papers [8,17]. Realizing that the models were inconclusive, the expert council accepted basic calculation parameters for estimating reserves at the Bazhenov. If the deposits are tested and a flow of oil to the well is produced, the net pay thickness is to be taken as 1/3 of the high-resistance part of the formation, and the values of open porosity and saturation are taken equal to 8% and 85%, respectively [18]. Obviously, such an approach is extremely basic and has no practical value.

The lack of information on all the core materials was not the key obstacle however. In the early stages of the study of the Bazhenov Formation, the impact of well design and methods of penetration on the oil flows produced were observed. Experts were constantly engaged in debates, which have been continued to this day, about the best well design for the Bazhenov Formation. Much work has been done in this area [12,15,16], but the original problems still remain. Current thinking dictates that the most effective way of well completion in the Bazhenov Formation is the use of a slotted liner. This completion method was proposed by F.G. Gurari, who discovered the Bazhenov formation [19].

A significant decline in the study of the Bazhenov took place during the 1990’s, and interest was only rekindled in 2006 when the RITEK company received a license to develop the Middle Nazym and Galyanov fields where the main prospecting developments are associated with the Low Tutleym subformation – an analogue of the Bazhenov Formation in the west of Western Siberia [19]. In 2007, based on logging data obtained from an open hole, a few studied core samples and PLT data of natural flowing wells, the specialists of CJSC “MiMGO n.a. V.A. Dvurechensky” under the leadership of V.S. Slavkin, hypothesized that the main inflow intervals in the Bazhenov Formation in these fields are tight carbonized fractured streaks (TCFS) [20]. This hypothesis was at odds with the prevailing basic theory that the main inflow intervals in the Bazhenov Formation are organic rich shale, foliated and sheeted abnormally high formation pressure (AHFP) [13,15,16]. For the development of the Bazhenov Formation this fact is of crucial importance. In the case of foliated shale, the permeability is due to the availability of AHPP that supports the void space between individual layers, so artificial lift, which creates significant drawdown pressure on the formation, is absolutely contraindicated for such reservoirs. If artificial lift is used, the space between layers will collapse, permeability will disappear, the well will cease to produce oil, and the pump will fail. The TCFS hypothesis actually claimed that the reservoirs have a hard framework, and due to significant drawdown pressures the permeability will not disappear. In fairness it should be noted that one of the first who began to associate productivity of the Bazhenov Formation with tight streaks was M.Y. Zubkov and his colleagues [21,22], who called these interlayers “potentially productive” (PPI).

In 2007, the Middle Nazym field of the Bazhenov was operated with ESPs, and test runs were conducted to stimulate inflows by pumping acid into the formation. By mid-2009 more than one third of all production stock in the Middle Nazym was being mechanically produced, and the most effective way to stimulate the inflow was acid treatment of the bottom hole [8,23]. After studying the core samples, it was found out that the main oil bearing beds in the Bazhenov Formation to the west of the Ob River Region are transformed radiolarite layers, which, depending on the nature of these transformations, are either aporadiolarite limestone, dolomite or silicite (silica radiolarite) [24,25,26, 27]. These interlayers are mainly porous fractured voids, with some porosity at 16%, and permeability is at 10 mD. Log curves display them as tight streaks [8,20,23].

Many researchers now recognize that, in the Ob River Region at least, commercial oil bearing capacity of the Bazhenov Formation is associated with the presence of tight streaks of secondary radiolarites and Bazhenov underlying carbonate layer COP1 [17]. They are easily recognizable from the log data, and the main task for geophysicists is learning how to evaluate the reservoir properties and forecast their dimensions. The contrasting properties of these layers make it possible to use seismic data to identify the most productive zones. Such works are now being actively performed in the Federal State Unitary Enterprise “VNIGNI”, CJSC “MiMGO” [8, 40, 41], Moscow State Lomonosov University [42] and in the LLC “ZapSibGTs”.

Currently, pilot commercial development of the Bazhenov Formation is being undertaken by three companies: Surgutneftegaz, Rosneft and RITEK. The highest activity is carried out by Surgutneftegaz, which has drilled more than 600 wells in the Bazhenov Formation over the last 30 years. The drilling results indicate that 37% of the wells were “dry”, 63% had oil flows (maximum up to 300 tons/day). In 2011, Surgutneftegaz produced 512 Ktons, Rosneft produced 82.4 Ktons, and RITEK in 2010 produced 117 Ktons of oil from the Bazhenov Formation [4, 28, 29].

The scope of outstanding issues, together with the giant light oil resources have attracted and continue to attract geologists of all levels ranging from young specialists to members Academy of Sciences and the Russian Academy of Sciences to solve the problems of the Bazhenov Formation. At different times, this problem was studied and is still being studied by the most eminent petroleum geologists of the USSR and Russia, namely members of the RAS A.E Kontorovich, I.I. Nesterov, member of the USSR Academy of Sciences and the Russian Academy of Sciences A.A. Trofimuk and many others. From the first oil blowout to the present day, 92 fields of light oil have been discovered within the Bazhenov Formation deposits [2], multiple methods of inflow stimulation have been trialled, including multi-stage hydraulic fracturing in horizontal wells that’s has proven to be successful in the shale deposits of North America. The production rates and statistics speak for themselves however. Even with its vast resources the aggregate oil production from the Bazhenov Formation only slightly exceeds 5 million tons for the whole history of the development [4,28, 29, 12].

Looking back at the experience that has been accumulated, one can conclude that over the last 45 years a lot of work has been done in terms of studying the Bazhenov Formation. However, no modern oil companies are capable of implementing research programs comparable in scope to those already done. Positive changes in the geological study of this challenging field can only be achieved based by identifying weaknesses or inconsistencies in the historical research, data and experience. The main drawback of previous experience is the incomplete geological data. Only a 100% core recovery from producing wells, along with a wide range of geophysical, reservoir, geological, technological and laboratory studies will allow us to conclusively determine what characteristics enable the flow of oil into wells in certain intervals, and where the greatest oil resources are concentrated. Only with a sufficiently complete set of studies can we identify the most effective way of describing the properties of the Bazhenov Formation. Until now, such work has only been performed on two SPD wells drilled in the Upper Salym field. But this geological knowledge itself cannot guarantee the success of the entire project without the proper organization of the development technique.

The uniqueness of the Bazhenov as a shale formation is not only in its size (more than 1 million km2), but its natural oil flow, which distinguishes it from other shale formations around the world. There is not any shale formation in the world with natural flows as thick as those of the Bazhenov. It can produce hundreds of cubic meters of natural flow oil per day, or, in more than a third of the wells drilled, no production whatsoever .

The highest flow rate shown in official statistics totalled 1248 m3/day and was produced in vertical exploration well 141-R at the Salym field [15].

The availability of wells with a large range of flow rates (from “dry” to hundreds of m3/day) has helped to define a strategy to study this formation in a completely different way than has been done for other shale formations around the world. For example, if in other countries shale formations have been studied in terms of using well interventions for development, Russian scientists and geologists concentrate on the development of “sweet spots”. This is the fundamental difference between the Western and Russian approach. On this basis, one of the areas that is still not well defined in Russia is the technical aspects of well stimulation and design optimization to develop the Bazhenov. Therefore, Russian oil and gas companies will form alliances with foreign companies that possess the latest shale production technologies.

In conclusion, the main weaknesses that currently exist in terms of developing the Bazhenov are incomplete geological data and limited study, which only focussed on remote methods of searching highly producing zones, and the question of oil production techniques in low-permeability zones have not been sufficiently studied. Bearing this in mind, the most valuable experience can gained from the studying the development of the Bakken Formation in the United States.

Breaking the Bakken Code
The date of birth of the unconventional industry in North America can be traced back to 1821 when, near Fredonia in the state of New York, local gunsmith William Hart drilled the first gas producing well from the Upper Devonian deposit of Dunkirk shale formation. This well had a depth of 70 feet (21.3 m) and a diameter of 1.5 inches [30]. In 1859, Edwin Drake drilled his first well and proved that oil can be produced in large quantities, so interest in shale gas was lost until the 1970’s.

Unconventional oil production in the United States started much later however, after Amerada Petroleum drilled its first producing well at Bakken in 1953. The formation was named after Henry Bakken, who owned the land in North Dakota where these deposits were first found. In the same year, geologist J.W. Nordqvist formally described the Bakken Formation as a source rock rich in hydrocarbons, which saturated the surrounding reservoirs due to migration of oil [31].

Commercial experience of the Bakken was started by the Standard oil and gas company in 1953, with well #1 at Woodrow Starr. Full development of the field started in 1955 and lasted until 1960. The main pay zones were the Sanish and Bakken formations (the upper part of the underlying Three Forks deposits). In all, 44 vertical wells were drilled in the Bakken Formation with an average production rate of 200 barrels (31.8 m3) per day; the accumulated production for its commercial lifetime totalled 11 million barrels (1.7 million m3) of oil and 20 billion cubic feet (0.57 billion m3) of gas [32]. The field was developed using a 40-acre (~ 16.2 Ha) well coverage.This fairly high productivity was due to the natural fractures caused by the steeply ascending subsurface structures [33]. Further development of the Bakken however was deemed unprofitable.

The 1970’s witnessed a decline in natural gas production from conventional fields, and the U.S. Government stimulated research projects in order to develop technologies to increase production. This led to technological advances in directional and horizontal drilling, seismic imaging, as well as in the technologies of massive hydraulic fracturing (HF). From 1980-2000, in order to test the effectiveness of new technologies, the U.S. Federal Government introduced tax benefits for 29 unconventional fields that triggered a new wave of interest in the shale gas industry [34].

Indeed, the first horizontal well in the Bakken Formation was drilled in 1987 by Meridian Oil, Inc. This well, #33-11 MOI, was initially drilled vertically, cored, logged and tested. The tests showed that it was a low producing well. Meridien then decided to drill a horizontal wellbore with a length of 2,603 feet (793.4 m) drilled in the upper part of the formation with a thickness of 8 feet (2.4 m). The well was completed on September 25, 1987 with flow rates of 258 barrels (41 m3) of oil and 299K cubic feet (8.5 km3) of gas per day. In all, during the period of its operation, this well produced 357,671 barrels (56.9 km3) of oil and 6381 barrels of water (1.01 km3). [31]

Due the a fall in oil prices in the 1990s, most companies abandoned their shale oil and gas experiments. Dick Finlay, affectionately known as the “Father of Bakken” did not give up however and is widely credited with “Breaking the Bakken Code” in 1996. His discoveries led to the development of the giant Elm Coulee Field in eastern Montana, now known as the “Sleeping Giant”. Findlay’s discovery was so significant that in 2006, after 10 years after the discovery, he was awarded the title of the Explorer of the Year [31]!

SPD 3

Findlay’s discovery lay in the fact that a few miles from Sidney, Montana, in the Bakken formation, he found a layer of dolomite between two layers of shale (Fig. 1). He later discovered in other areas grained sandstone with a high content of carbonate material [36]. In both cases, these rocks had reservoir properties that were insufficient for development. It is well known that dolomite and sandstone that include voids are good for oil reservoirs. Findlays theory was very simple: if you drill a well in dolomite and create a system of fractures in the right direction, it will become a reservoir for oil, which will saturate the surrounding shale source rocks. Findlay was hoping that unlike other methods, this approach would make oil production from the huge Bakken formation profitable. To try this theory, Findlay needed a sponsor who had money and experience of horizontal well hydraulic fracturing. His dream came true when Halliburton decided to check out his
theory. [31]

In 1998, Halliburton invested in several programs to drill the Bakken, which started in early 2000. The first well, which was named in Halliburton as the “Burning Tree State” was expected to have a vertical bore of 10,000 feet (3048 m) and a horizontal bore of 3,000 feet (914.4 m). Because of drilling problems the well was drilled to a depth of 12,000 feet (3657.6 m), but this did not prevent the hydraulic frac program and completion of the well from being fully implemented. As a result, the oil production rate exceeded all expectations [31]!

The success of Halliburton inspired other companies to actively develop the Bakken. At the same time, the U.S. Geological Survey (USGS) began a study to determine the actual reserves, and how it would affect the production of oil in the United States, which at that time was at a record low. What the USGS found surprised even them and caused a sensation in the national press for many years. The U.S. Energy Information Administration (EIA) forecast indicated that that U.S. oil companies could expect to harvest a whopping 503 billion barrels of oil (80 billion m3) from the Bakken formation! [31]

SPD 4

The well-proven approach to developing Bakken is to penetrate the dolomite/sandstone of Middle Bakken with horizontal wells, have long horizontal wellbores (5000-10000 feet or 1524-3048 m) and then perform multistage hydraulic fracturing in consecutive sections [36] (see Fig. 2.) Basically, it turns out that the productivity of the wells was largely due to where they were drilled. The most successful wells were drilled in areas characterized by natural fracturing [33].

Today, the Bakken is one of the largest continuous hydrocarbon accumulations in the world. The reservoir is characterized by AHFP, so the wells have high initial production rates. Pressure at the Bakken exists because the conversion of organic substances far exceeded its original volume and because its inability to leave the oil source rocks it remains “locked” inside. The availability in the Bakken of low porosity layers of dolomite and sandstone susceptible to fracturing, which initially have low permeability and reservoir properties, allows operators to use hydraulic fracturing to create an extensive system of drainage channels. Abnormally high reservoir pressures, combined with the benefit of artificial well intervention of the flows, allows each drilled well to produce from 600K to 700K barrels (95.4-111.3 km3) of oil during its lifetime [31].

Oil production in North Dakota started to grow in 2008, and reached 150K barrels (23.8 km3) per day. In 2012, North Dakota had already started producing 768K barrels (122.1 km3) of oil per day from more than 3,000 operating wells. Production growth totalled 412% in just four years [31]. If this is not a boom, then what is it?!

Thus, the main lesson to be learned from the experience of the development of the Bakken shale formation in the United States can be summarized as follows. Despite its name, the “shale oil” is not produced from shale, but from layers of dolomite and sandstone, deposited within the shale formation. Initially, these rocks have low reservoir quality, but hydraulic fracturing creates an additional fractured system, which results in the interlayers of dolomites and sandstones becoming sufficiently permeable for oil recovery. The development of these beds using horizontal wells can significantly increase the extent of fluid movement.

In part 2 of this article, in the next issue of ROGTEC, we will look at the search for the “Middle Bakken” at the Bazhenov formation.

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