Gazprom Neft: Developing Unconventional Hydrocarbons

Kirill Strizhnev, Head of «Challenging Reserves» project office for Gazprom Neft’s Directorate of the exploration and resource base development

Modern global estimates of unconventional hydrocarbon reserves all point to huge development potential. Currently, unconventional oil and gas production only account for about 1% of global output, however the development of unconventional reserves is demonstrating steady growth and the potential to compete with production from traditional reserves. It is estimated that by 2020-2025, unconventional oil and gas production will rise to 5% of global output.

In Russia, shale oil is the main focus in terms of unconventional hydrocarbons. Extensive domanicoids found within oil and gas reservoirs at the Bazhenov formation, as well as documented commercial production raise the possibility of large scale production when the latest technology is implemented. Some experts predict that oil production at the Bazhenov suite could hit 15-20 million tonnes by 2020, and 70 million tonnes by 2030.

At Gazprom Neft, we currently have a number of shale oil projects underway. In particular, Salym Petroleum Development, a joint venture between Gazprom Neft and Shell, operating in the Khanty-Mansi Autonomous Okrug, is looking at the potential of shale oil deposits in the area. Gazprom Neft itself is also looking at the potential of the Bazhen and Abalak suites at Palyanovskaya area of Krasnoleninskoye oil-gas-condensate field. The north-eastern part of Palyanovskaya area, which is part of the Krasnoleninskoye OGCF, lies within the territory of the Octyabrskiy district of KMAO (fig.1). The Krasnoleninskoye field’s main producing areas, Yem-Yegovskoye and Talinskoye border the Palyanovskaya area on the west and the Kamennoye area on its south-east.

The Palyanovskaya area was commissioned for commercial production in 1992. Active drilling and field development started when the Vikulov suite began to be developed in 1997. As of May 2013, the field has 79 wells, 13 of which are injection wells. The production comes mainly from VK and YuK units.

The main pay zones at the Palyanovskaya field are the Vikulov suite formations (VK1, VK2), Bazhenov (Tutleim) suite formations (YuK0-YuK01), Abalak suite formations (YuK1), Tyumen suite formations (YuK2-3, YuK4, YuK6) and other basal layer formations.

Despite the significant total geological reserves of Bazhenov suite (about 40 mln t) and numerous oil inflows (indications of shale oil were found while drilling 25 appraisal and 10 production wells), the development of this unique asset is still in early stages. The reason for this is because reservoirs at the Bazhenov have a complex structure and require a detailed study of deposit distribution patterns and composition. During the extensive drilling program in the 1990’s, reliable formation testing and well stimulation methods were unavailable, which in a number of cases might have led to negative test when in fact commercial oil was present.

In any case, no proven technologies existed at the time to develop reservoirs of this type. All of these were the major obstacles faced when trying to develop the Bazhenov.

In 2011, based on structural deformation analysis of 3D seismic data, an experimental study was undertaken to understand and forecast the Bazhenov-Abalak, a system fractured-cavernous reservoir development zones at Palyanovskaya field. As part of the study, the fractured reservoir zones were mapped. Through specialized processing of 3D field seismic data, and based on structural deformation analysis, a fractured-block model for the research area was created. The fracture zones were categorized based on activation and intensity of dynamic parameters within the target interval of Bazhen-Abalak system. Production parameters were analyzed, as was the history of the historical wells. From this, recommendations were given for field development in terms of well workover in existing wells, and where production wells should be drilled.

The fractured-block structure of the Palyanovskaya field was formed by two fault systems and form stable tectonic pairs. This was identified based on 3D seismic results for the area. The first fault system is submeridianal, the second is sublatitudinal.

The size of blocks formed with submeridianal and sublatitudinal systems average about 750 meters.  Both fault systems are confined to axial zones, which is an individual characteristic of field structures in this part of the Krasnoleninskiy arch. Local maximum elevation amplitudes are confined to fault centers within elevations.

Pilot production at the field started in the fall of 2012, when 5 already drilled wells were reentered. Following this, the company then commenced drilling at appraisal well № 153 and sampled its core.

When comparing the results obtained from the core sample with the data for the YuK01 reservoir, the data gives grounds to the claim that the fractured block structure is the determining factor for production capacity of wells at Palyanovskaya field, as well as other earlier explored KMAO fields. The largest production rates are seen in wells located less than 100 from axial fracture zones and fault centers. For example, well № 153 demonstrated oil flow exceeding 80 t/day.

Categorization of the core samples in the Bazhenov suite demonstrated low radiolarite content for six wells. The total thickness of radiolarite interlayers was about 0,4 m from all core samples at Bazhenov suite for well № 153, and was even less for well № 601. On this basis, we have no grounds to relate radiolarite, and potentially oil-bearing carbonatized interlayers to the volume of potential oil production. Bearing this in mind, we can consider that the fracture component is the source of potential oil production.

A total of seven main lithotypes were identified for Bazhenov suite (lower subsuite) in deposits (fig.2) of the YuK0-YuK01 reservoirs in the north-eastern part of Palyanovskaya field, and are found between 2216 & 2414 m below sea level. The formation represents a compartmentalized reservoir consisting primarily of secondary interstices. Lithologically, the YuK0-YuK01 reservoir primarily consists of argillites with carbonate interlayers.

The overall thickness of YuK0-YuK01 reservoir averages 25,7 m; with a maximum thickness of 28,5 m which was recorded for well № 23 in the south-western part of the field.  The minimum reservoir thickness is 21 m and is found in well №12338 in the western part of the field. There is a certain pattern to the reservoir thickness which depends on the structural plan.

Based on the results of GIS data interpretation, the net thickness of reservoir YuK0-YuK01 varies from 0,6 m (well № 463P) to 9,8 m (well № 42Р), and decreases in its central part, and increases towards the margins. Then average reservoir thickness is 5.8m, and the net oil pay thickness has the same characteristics as the net reservoir thickness.

As of today, only one hypothesis related to distribution of pay zones is applicable, and that is to target clusters of “corridor” fractures. In the model created for Palyanovskoye field (fig.3), the main fluid-bearing fault zones from the pre-Jurassic complex to the Frolov suite run parallel to distribution of sub-Urals force line system. When analyzing the oil follows and production data this concept is confirmed.

The next steps in developing this project will include further drilling at the field. We are looking to drill a well in the near future to uncap the center of the intersection between the submeridianal and sublatitudinal striking fracture zones. The well will be located in direct proximity to the north-east striking fracture zone, which based on the data, is promising in terms of potential production. We are planning a second well to uncap the fracture zone intersection, but at lower hypsometric levels, and a third well will be drilled at the intersection of the north east fracture zone, similar to well № 153.

Drilling layers located at lower hypsometric levels contain pre-Jurassic deposits, and carrying out the relevant research in three new wells will provide data to evaluation reservoir properties and their production data. This will help provide the information needed to overcome challenges that include:
»    Lack of clear understanding about the reservoir, its lithology and capacity properties, and unknown reserves;
»    Lack of fracturing indicators as well as information on density and size of fractures;
»    Lack of reliable data on current operating wells and little understanding of the net pay thickness and filtration;
»    Steep declines in previously operated wells and therefore no reservoir models for comparison;
»    Unknown influence of withdrawals to the density of remaining reserves and formation pressures (consequence of points 1 and 2).

The key objectives for the next stages of filed development are to drill higher elevations, sidetracking, testing horizontal drilling and multistage fracturing technologies as well as testing chemical and physical well stimulation methods. For some of the wells at the Frolov, Bazhenov and Abalak suites, we plan to carry out core sampling, geophysical research and dynamic well testing.

In summary, it is safe to say that development of shale oil at Krasnoleninskoye field is moving in the right direction. Moving forward unconventional field development will help to extend the lifecycle of our conventional fields and indeed the experience we have gained at the Palyanovskaya field will be useful for new projects.