Predicting the present-day in situ stress distribution within the Yanchang Formation Chang 7 shale oil reservoir of Ordos Basin, central China

Wei Ju,Hao-Ran Xu,Sheng-Bin Feng,Ke Xu,Yuan You,Geoff Wang,Xiao-Bing Niu

doi:10.1007/s12182-020-00448-8

Abstract

The Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin is important in China for producing shale oil. The present-day in situ stress state is of practical implications for the exploration and development of shale oil; however, few studies are focused on stress distributions within the Chang 7 reservoir. In this study, the present-day in situ stress distribution within the Chang 7 reservoir was predicted using the combined spring model based on well logs and measured stress data. The results indicate that stress magnitudes increase with burial depth within the Chang 7 reservoir. Overall, the horizontal maximum principal stress (SHmax), horizontal minimum principal stress (Shmin) and vertical stress (Sv) follow the relationship of Sv ≥ SHmax > Shmin, indicating a dominant normal faulting stress regime within the Chang 7 reservoir of Ordos Basin. Laterally, high stress values are mainly distributed in the northwestern parts of the studied region, while low stress values are found in the southeastern parts. Factors influencing stress distributions are also analyzed. Stress magnitudes within the Chang 7 reservoir show a positive linear relationship with burial depth. A larger value of Young’s modulus results in higher stress magnitudes, and the differential horizontal stress becomes higher when the rock Young’s modulus grows larger.

Highlights

With the continued development of hydrocarbon theories and recent exploration practices, the global oil and gas industry has gotten into the period of unconventional hydrocarbon resources
The objective of this study is to predict the present-day in situ stress distribution within the Yanchang Formation Chang 7 shale oil reservoir and analyze the influencing factors
Within the Yanchang Formation Chang 7 shale oil reservoir of Ordos Basin, the SHmax, Shmin and Sv magnitudes all increase with burial depth

Summary

Introduction

With the continued development of hydrocarbon theories and recent exploration practices, the global oil and gas industry has gotten into the period of unconventional hydrocarbon resources. The unconventional shale oil and gas, tight oil and gas, gas hydrates and coalbed methane have shown great potential under the present-day economic and technological conditions, and their production has changed the global energy consumption structure (Jia et al 2012; Zou et al 2013; Vedachalam et al 2015). Among those unconventional resources, shale oil is defined as a kind of nongaseous hydrocarbon with great exploration and development potential, which is generally accumulated in mudstone and shale layers in multiple states (Zhang et al 2012, 2015; Zou et al 2013). In the Ordos Basin, shale oil resources are largely accumulated in the Yanchang Formation Chang 7 oil-bearing layer, and the estimated amount is more than 10 × 108 tons (Yang et al 2013)

Objectives

Methods

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Conclusion