Open Access

ARTICLE

Characteristics of Rock Mechanics Response and Energy Evolution Regime of Deep Reservoirs in the Bozhong Sag, Bohai Bay Basin

by Suogui Shang¹, Kechao Gao¹, Qingbin Wang¹, Xinghua Zhang¹, Pengli Zhou^2,3,*, Jianhua Li^2,3, Peng Chu^2,3

1 Tianjin Branch of CNOOC Limited, Tianjin, 300459, China
2 Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Institute of Deep Earth Sciences and Green Energy, Shenzhen University, Shenzhen, 518060, China
3 College of Civil and Transportation Engineering, Shenzhen Key Laboratory of Deep Engineering Sciences and Green Energy, Shenzhen University, Shenzhen, 518060, China

* Corresponding Author: Pengli Zhou. Email:

(This article belongs to the Special Issue: Hydraulic Fracturing Theory and Application for Geo-energy Development)

Energy Engineering 2024, 121(9), 2505-2524. https://doi.org/10.32604/ee.2024.050094

Received 27 January 2024; Accepted 12 April 2024; Issue published 19 August 2024

Abstract

Hydraulic fracturing is a mature and effective method for deep oil and gas production, which provides a foundation for deep oil and gas production. One of the key aspects of implementing hydraulic fracturing technology lies in understanding mechanics response characteristics of rocks in deep reservoirs under complex stress conditions. In this work, based on outcrop core samples, high-stress triaxial compression tests were designed to simulate the rock mechanics behavior of deep reservoirs in Bozhong Sag. Additionally, this study analyzes the deformation and damage law for rock under different stress conditions. Wherein, with a particular focus on combining energy dissipation theory to further understand damage law for deep reservoirs. The experimental results show that regardless of stress conditions, the process of deformation/failure of deep-seated reservoirs goes through five stages: Fracture compaction, new fracture formation, stable fracture expansion, unstable fracture expansion, and post-peak residual deformation. Under different stress conditions, the energy change laws of specimens are similar. The energy dissipation process of rocks corresponds closely to the trend of deformation-failure curve, then displays distinctive stage characteristics. Wherein, in stage of rock fracture compaction, the input energy curve is approximately coincident with the elastic strain energy curve, while the dissipation energy curve remains near zero. With the increase of strain, the growth rate of elastic strain energy increases gradually, but with the deformation entering the crack propagation stage, the growth rate of elastic strain energy slows down and the dissipation energy increases gradually. Finally, in the post-peak stage, rock fracture releases a lot of energy, which leads to the sharp decline of elastic strain energy curve. In addition, the introduction of damage variable D quantifies the analysis of the extent of failure for rocks. During the process of increasing strain, rock damage exhibits nonlinear growth with increasing stress.

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