Geomechanical Analysis for Deep Shale Gas Exploration Wells in the NDNR Blocks, Sichuan Basin, Southwest China

Majia Zheng,Hongming Tang,Hu Li,Cui Jing,Jian Zheng

doi:10.3390/en13051117

Abstract

The abundant reserve of shale gas in Sichuan Basin has become a significant natural gas component in China. To achieve efficient development of shale gas, it is necessary to analyze the stress state, pore pressure, and reservoir mechanical properties such that an accurate geomechanical model can be established. In this paper, Six wells of Neijiang-Dazu and North Rongchang (NDNR) Block were thoroughly investigated to establish the geomechanical model for the study area. The well log analysis was performed to derive the in-situ stresses and pore pressure while the stress polygon was applied to constrain the value of the maximum horizontal principal stress. Image and caliper data, mini-frac test and laboratory rock mechanics test results were used to calibrate the geomechanical model. The model was further validated by comparing the model prediction against the actual wellbore failure observed in the field. It was found that it is associated with the strike-slip (SS) stress regime; the orientation of SHmax was inferred to be 106–130° N. The pore pressure appears to be approximately hydrostatic from the surface to 1000 m true vertical depth (TVD), but then becomes over-pressured from the Xujiahe formation. The geomechanical model can provide guidance for the subsequent drilling and completion in this area and be used to effectively avoid complex drilling events such as collapse, kick, and lost circulation (mud losses) along the entire well. Also, the in-situ stress and pore pressure database can be used to analyze wellbore stability issues as well as help design hydraulic fracturing operations.

Highlights

Shale gas resource is the fastest growing natural gas resources in exploration and development of unconventional oil and gas resource over the world
The analysis of the drilling events that may be related to mechanical instability of the wellbore, can be used to help derive parameters of the geomechanical model and calibrate/verify the model
The model wasmodel verified by drilling events, and the The results show that the prediction resultsmodel of the provides guidance for the subsequent drilling construction in this area and can be used to effectively geomechanical model match the actual observations

Summary

Introduction

Shale gas resource is the fastest growing natural gas resources in exploration and development of unconventional oil and gas resource over the world. In order to achieve efficient development of shale gas resource in the area, it is necessary to analyze the stress state, pore pressure and reservoir mechanical properties to establish a precise geomechanical model, avoiding complex drilling such as collapse, kick, mud losses, and so on. A geomechanical model is made up of five principal components, which are the three principal stresses, pore pressure, and rock mechanical properties. The magnitudes and orientations of the principal stresses make up the in-situ stress tensor [4,5]. They interact with the other two geomechanical components, the pore pressure and the rock strength, to induce geomechanical issues during drilling, for example, wellbore breakouts, drilling fluid losses and sand production

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Results

Discussion

Conclusion