Simulation of paleotectonic stress fields within Paleogene shale reservoirs and prediction of favorable zones for fracture development within the Zhanhua Depression, Bohai Bay Basin, east China

• Published in: Journal of petroleum science & engineering Vol. 110; pp. 119 - 131
• Main Authors: Jiu, Kai, Ding, WenLong, Huang, WenHui, You, Shenggang, Zhang, Yeqian, Zeng, Weite
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01.10.2013; Elsevier
• Subjects: Applied sciences; Basins; Bohai Bay Basin; China; Crude oil, natural gas and petroleum products; Depression; Energy; Exact sciences and technology; finite element method; Fracture mechanics; fracture prediction; Fuels; Geology and geochemistry. Geological and geochemical prospecting. Petroliferous series; Natural gas; paleotectonic stress field; Prospecting and exploration; Prospecting and production of crude oil, natural gas, oil shales and tar sands; Reservoirs; Shale; shale reservoir; Stresses; tectonic fractures; Asia; China; INW, Bohai Sea, Shahejie Formation; INW, Bohai Sea, Bohai Bay; fracture prediction; paleotectonic stress field; shale reservoir; finite element method; Bohai Bay Basin; tectonic fractures; Paleogene; Stress analysis; Shale; Reservoir; Fracture; Tectonics; Finite element method; Simulation
• DOI: 10.1016/j.petrol.2013.09.002
• ISSN: 0920-4105

Tectonic fractures are the most important reservoir spaces within shale reservoirs and can significantly improve the permeability of a reservoir, the development and distribution of these fractures are controlled by paleotectonic stress fields. An important hydrocarbon reservoir is hosted by a Paleogene shale unit within the lower section of the third member of the Shahejie Formation (Es3) within the Zhanhua Depression of the Bohai Bay Basin, east China. Industrial-level oil and gas production has been obtained from over 30 wells with the highest single well production of 93t/d, indicating the large oil and gas potential of these reservoirs in the Zhanhua Depression. The data obtained from cores, logs, and drilling in the Zhanhua Depression can be used to identify the processes involved in the development of such tectonic fractures. In this study, these data were combined with additional acoustic emission and rock mechanics data to identify the effects of faulting and lithological variations on the development of fractures using a finite element method (FEM) stress analysis approach that simulated paleotectonic stress fields during the late Dongying stage, the period of time when the majority of the fractures developed. Estimations of rock failure criteria and comprehensive indexing of rupture rates for tectonic fractures were undertaken to determine the quantitative development of fractures and to predict favorable zones for fracture development. Tectonic fractures within the shale reservoir in the lower part of the Es3 unit include both tensional and shear fractures, these fractures are generally unfilled or half-filled. The NE–SW strike of these fractures is consistent with the orientation of the present stress field, meaning that these fractures were high-priority targets during initial well targeting. Tectonic fractures can be identified during logging by increased resistivity (R2.5), increased acoustic time difference (AC) values combined with cycle skip of the peaks, and highly variable but generally elevated gamma ray (GR) values. Fractures can also be directly identified, and fracture parameters can be determined using Formation MicroScanner Image (FMI). The magnitude of the maximum principal stress during the major period of fracture development within the Zhanhua Depression was 53.2MPa, and the paleotectonic stress field was controlled by the location of fault zones. In contrast, areas without fractures have stress fields that were influenced by lithological variations, leading to the development of high stress fields in areas with rocks containing high concentrations of carbonate. Fracture development is controlled by tectonic stress fields and fractured areas are generally located between fault zones, at the intersection of faults, in areas when fault orientations change, and at high stress areas near fault tips. The present results regarding predictions of the locations of fractured areas are consistent with the location of producing oil and gas wells. •The characteristics of lacustrine shale fracture in the Bohai Bay Basin.•Simulation of the paleotectonic stress field with shale reservoir.•The prediction of favorable zones for shale tectonic fracture development.•The effects of faults and lithology on the distribution of shale tectonic fracture.