Earth Science Frontiers ›› 2024, Vol. 31 ›› Issue (5): 263-287.DOI: 10.13745/j.esf.sf.2024.6.27

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Fractures in Ordovician carbonate rocks in strike-slip fault zone, Shunbei area: Fracture distribution prediction and fracture controlling factors

LI Yuntao1,2(), DING Wenlong1,2,*(), HAN Jun3, HUANG Cheng3, WANG Laiyuan3, MENG Qingxiu3   

  1. 1. School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China
    2. Key Laboratory for Marine Reservoir Evolution and Hydrocarbon Abundance Mechanism (Ministry of Education), China University of Geosciences (Beijing), Beijing 100083, China
    3. Exploration and Production Research Institute, Sinopec Northwest Oil Field Company, ürümqi 830011, China
  • Received:2023-11-15 Revised:2024-05-22 Online:2024-09-25 Published:2024-10-11

Abstract:

Tectonic fractures are one of main reservoir spaces in carbonate rocks, which can provide a good conduit for oil and gas transportation and reservoir space in tight limestone. The development of tectonic fractures is affected by various factors such as tectonic location, lithology, reservoir thickness, temperature, peripheral pressure and tectonic faulting, among which tectonic faulting caused by local tectonic stress in the regional tectonic stress field is an important factor controlling the development of tectonic fractures. In view of the characteristics of carbonate reservoirs and fracture development, we use the inversion function of rock mechanical parameters based on 3D seismic data volume, calibrated using dynamic rock mechanical parameters for a single well, to obtain a non-homogeneous rock mechanical model to improve the authenticity and accuracy of mechanical parameters in the model in the simulation of the stress field. Using the method of self-adaptive boundary condition constraint the optimal boundary conditions are automatically obtained when the error between the simulation and measured results is minimized, significantly improving the accuracy and reliability of the stress field simulation. On this basis, the fracture development characteristics and fracture activity in reserviors in the SHB16 fault zone and adjacent areas are quantitatively characterized using parameters including reservoir tensile rupture rate, shear rupture rate, comprehensive rupture rate, horizontal stress difference, stress difference coefficient, and sliding trend coefficient for the fault plane. We carried out qualitative and quantitative investigation into the effect of controlling parameters, such as horizontal stress difference, distance from faults and fault activity intensity in the vertical direction, on the fracture development characteristics; the correlations between variables were quatified using Spearman’s rank correlation coefficient. On the basis of clarifying the controlling factors of reservoir fracture development, we constructed the reservior development indexes for Ordovician carbonate reservoirs to classify the Ordovician carbonate reservoirs into categories I-IV from the best to the worst, and clarified the correlation between the deformation modes of the strike-slip faults and the degree of fracture development in sizable reserviors, further establishing the geologic model under different reservoir categories. The above results not only improve the accuracy and reliability of quantitative prediction of fracture development characteristics and multiparameter distribution rules based on stress field simulation, but also have significant importance for speeding up the exploration and development process of carbonate reservoirs.

Key words: Shunbei area, Ordovician carbonate reservoirs, tectonic stress field simulation, quantitative prediction of fracture multiparameter distribution, quantitative evaluation of reservoir scale

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