Abstract

The interests of many leading oil companies of the world have turned to the oil shales. Significant volumes of hydrocarbons concentrated in oil source rocks stimulate a constant search for technologies for the evaluation and production of hard-to-recover reserves both from operators and the state.

The segment strategy of hard-to-recover stocks (TRIZ) is formed in Rosneft Oil Company. According to strategy, a nonconventional reservoirs of the Bazhenov-Abalak complex (BAC) of developed by JSC RN-Nyaganneftegaz the Krasnoleninsky District are defined in the first group of effectiveness.

The reservoirs contain significant oil reserves in YK0 and YK1 layers, but at the moment recovery from initial recoverable reserves is only 10%. Production is mainly in the Central section of the Em-Yegovsky field, which is characterized by the high density of the reserves.

Increasing of the drilling efficiency and a perspective of development is constrained not only by the lack of methods of forecasting productive zones and technologies for effective extraction of reserves from non-traditional reservoirs, but also by the extremely low level of study of the object. With the purpose of preparing reserves for industrial development, it is required to create a set of methods for studying and laboratory core research, estimation of reservoir parameters, methods for assessing the influence of process fluids, and non-standard approaches for forecasting productive zones and efficient extraction of non-traditional reserves.

In 2017, RN-Nyaganneftegaz JSC for the implementation of the 5-year project in order to select technologies for localization and extraction of reserves allocated a test site with an area of 400 square kilometers in the territory of the Em-Yegovsky license block. The explored polygon covers zones of different types of the Bazhenov-Abalak structure: there are areas of different density of faults and fractures (from low to extremely high), as well as different degrees of maturity of organic matter.

The central part of the local structure is covered by 3D seismic studies with increased multiplicity, as well as characterized by exploratory and operational drilling, which provided the core from the interval in 2016-2017.

At present, RN-Nyaganneftegaz JSC jointly with the Tyumen Petroleum Research Center is carrying out the research work based on a comprehensive study of the Bazhenov-Abalak complex in the Em-Yegovsky field. The program of scientific project includes:

  • Complex core studies: routine, special, mineralogical, lithological, geochemical, pyrolytic, thermophysical and geomechanical studies, determination of porosity and permeability, study of the structure and maturity of organic matter, pore space structure by microtomography, mercury porosimetry.

  • Construction of mechanical and petrophysical models of reservoirs and sediment coverings based on core data and geophysical data.

  • Testing various techniques for processing and interpreting seismic data to predict the properties of the deposits (porosity, permeability, brittleness, fracturing).

  • Improvement of methods and tools of geological modeling for mapping of productive zones of reservoirs.

According to the R & D program the types and volumes of research performed are multifaceted and cover various areas of knowledge. Within the framework of this article, the authors confine themselves to the results of a complex study of the material composition in order to clarify sedimentation environments in the sediments of the Bazhenov-Abalak complex of the Krasnoleninsky District.

Core studies were performed on 11 wells with maximum core removal and an extended geophysical complex.

Based on the core study results, the hypothesis of the facial conditions of sedimentation was put forward for further geological modeling of the object.

Krasnoleninsky fold is located in the southwest of the West Siberian oil and gas province and includes a number of areas, including the Em-Yegovsky field (Figure 1).
Figure 1

Overview of the work area

Figure 1

Overview of the work area

The Bazhenov-Abalak complex is widely developed on the territory of the Em-Yegovsky field and includes the Tutleima (analogue of the Bazhenov) formation and the underlying Abalak suite. In general, the object is maintained in area and is characterized by the following parameters (Table 1).

Table 1

Parameters of objects

ParametersTutleima Formation (Bazhen)Abalak formation
Depth, TVDSS, m −2230 −2265 
Thickness, m 35 25 
Formation temperature, °C 100 100 
Reservoir pressure, atm – 235 
ParametersTutleima Formation (Bazhen)Abalak formation
Depth, TVDSS, m −2230 −2265 
Thickness, m 35 25 
Formation temperature, °C 100 100 
Reservoir pressure, atm – 235 

Based on the results of testing and the history of wells, the main productive interval is confined to the top of the Abalak suite.

The received inflows are characterized by high initial oil rates up to 300 m3/day and a rapid decline in production and reservoir pressure, which indicates the presence of high-permeability filtration channels and limited drainage area. Individual wells have a significant cumulative production to hundreds of thousands of tons and a long period stable operation.

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