Development Characteristics and Quantitative Prediction of Multiperiod Fractures in Superdeep Thrust-Fold Belt

Jianwei Feng,Feng Qin,Junxiao Qu,Pengfei Zhang,Andrea Billi

doi:10.2113/2021/8895823

Jianwei Feng, Feng Qin + Show 3 more

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https://doi.org/10.2113/2021/8895823

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Abstract

Abstract For a superdeep imbricated thrust-fold belt in the Kuqa depression of Tarim Basin, NW China, the structural fractures have a great impact on the tight gas reservoir productivity. In this research, structural fractures were characterized from core data and imaging logging data. Numerically, the finite element (FE) method was applied to simulate the 3-D paleotectonic stress field of the key fracture-generating period as well as the present-day stress field in the Keshen gas field. Based on previously developed geomechanical models, we further derived the models of fracture aperture and porosity under the palaeostress field. A fracture permeability model considering fracture filling degree and stress was developed based on the Fracture Seepage Theory. Finally, we obtained a series of calculation models for the present-day fracture aperture and permeability. The predictions based on these models agreed well with actual measurement results, with most of the relative errors less than 20%. The developed 3-D FE geomechanical model and fracture parameter prediction method hold great promise for characterizing fractures in other deep low-permeability reservoirs.

Highlights

Fracture is the most widely developed fault structure in the upper crust, and its key difference from the fault is the indistinct displacement [1, 2]
(1) By comparing tectonic movement and fracture distributions, the macroscopic developmental features of fractures were summarized based on core observation and formation microimage logging (FMI) interpretation
Most shear fractures striking in NNW-SSE and NE-SW were formed mainly under NNW350° compression during Himalayan periods, and most tensile fractures striking in NEE-SWW and NWWSEE were formed under local extensional stress field induced by rapid fold uplift during the late Himalayan period

Summary

Introduction

Fracture is the most widely developed fault structure in the upper crust, and its key difference from the fault is the indistinct displacement [1, 2]. For deep/superdeep tight sandstones, structural fractures are widely developed due to their distinct characteristics from other conventional reservoirs, such as large burial depth, large pressure coefficient, high compaction, high reservoir heterogeneity, super-low permeability, and developed structural fractures [8,9,10,11,12]. This extensively developed structural fracture system is an important seepage channel and space of the tight sandstone reservoir and seriously affects the productivity of a single well [13,14,15,16,17]. Spatial quantitative characterization and modeling of complex fracture networks in deep or superdeep tight reservoirs within complex tectonic zones presents more difficulty [18,19,20]

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