Abstract

The article addresses a large area (a territory 100 km long and 80 km wide) encompassing several oil fields, including South Priobskoye, Chaprovskoye, Kondinskoye, Malokondinskoye, North Kondinskoye and West Kondinskoye. The breakdown of this huge and actually a single oil-and-gas bearing zone consisting of a series of sand lenses and containing 1.5 bln tons of recoverable reserves is rather tentative. The authors of this paper have been working in this area and participated in exploration, investigation and development of numerous fields within the Priobsky-Kondinsky zone. Due to complex geology of clinoform formations, low flow properties of the rocks, wide spacing of exploratory wells and seismic surveys, a number of fields situated in the southern part of the Frolovsky depression were brought into production 15 to 20 years later than expected. A significant engineering breakthrough in oil production occurred due to implementation of massive reservoir fracturing treatments and integrated approach to 3D seismic interpretation. These are the technologies that allowed successful development of low-permeability clinoform productive reservoirs within AS9-AS12 formations in all the fields discovered in this area. As of today, a great amount of 3D seismic surveys were shot in many license areas totaling over 3000 sq km. Production drilling and oil production in actually all the fields within the Priobsky-Kondinsky area involve massive frac jobs. Integrated interpretation of 3D seismic led to surprising results indicating the most complex geology of the Neocomian clinoform reservoirs including both tectonic processes associated with sediment slides, and formation of fans within turbide flows. Thorough insight into spatial position and forecasting of flow and storage properties of each sand body allows efficient drilling and development of low-permeability oil saturated reservoirs in the Priobsky-Kondinsky area.

Introduction

Several oil fields were discovered thirty years ago at the edges of the Frolovsky depression, their total recoverable reserves were estimated at 1.5 bln tons. Favorable geographic situation in the central part of the West Siberia and significant volumes of oil saturated reservoirs theoretically created all prerequisites for rapid development of the new fields. However these huge hydrocarbon reserves could not be brought into production for a long time. Southern part of Priobskoye field, Upper, Middle and Lower Shapshinskoye, Kondinskoye, Chaprovskoye, West-Erginskoye and Erginskoye fields were temporarily abandoned. The primary reason for which these fields could not be put on production was lack of appropriate reservoir engineering technology for AS9-AS12 formations exhibiting extremely low reservoir properties. Due to complex geology of clinoform formations, low flow properties of the rocks, wide spacing of exploratory wells and seismic surveys, a number of fields situated in the southern part of the Frolovsky depression were brought into production 15 to 20 years later than expected. There were two main causes that postponed all the activities in the fields for such a long time. One was low production rates obtained in exploratory wells (0.5 to 5.0 m3/d) despite considerable pay thicknesses varying from 10 to 70 m, the other being a complex lateral distribution of productive reservoirs. Lack of technology that would allow mapping the sand lenses and predicting their extension multiplied the risks associated with locating and drilling production wells.

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