Physicochemical Characteristics of Hard Brittle Shale and Associated Wellbore Instability

Abstract

Wellbore instability in hard brittle shale is a key problem restricting the effective development of deep resources and unconventional shale gas resources which has not been solved effectively. Based on this, different experiments including x-ray diffraction, scanning electron microscope, hydrate swelling test, rock mechanics test were conducted in order to understand the components and microcosmic structure of the hard brittle shale and its physicochemical characteristics comprehensively. In addition, the properties of the collapsing block from the borehole were analysed through comparison before and after soaked in water. The results showed that unlike soft shale, the content of water sensitivity mineral such as montmorillonite within hard brittle shale was low and swelling capability due to water absorption was consequently low, but internal micro-fractures were developed, so the main reasons of wellbore instability are possible not chemical factors, but that the crack propagation and strength weakened. In drilling engineering, effective countermeasures are mainly including two categories; one is improving drilling fluid properties such as sealing, rheological property, wettability to slow down the drilling fluid invasion into micro-cracks within hard brittle shale, and the other is increasing the strength and reducing the stress acting on the rock surrounding wellbore through increasing drilling mud column pressure, reducing disturbance and the impact of drilling tool, optimizing well trajectory and so on.

Copyright 2017, Shaanxi Petroleum Society.

This paper was prepared for presentation at the 2017 International Petroleum and Petrochemical Technology Conference in Beijing, China, 20–22 March 2017.

This paper was selected for presentation by the IFEDC&IPPTC Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the IFEDC&IPPTC Committee and are subject to correction by the author(s). The material does not necessarily reflect any position of the IFEDC&IPPTC Committee, its members. Papers presented at the Conference are subject to publication review by Professional Committee of Petroleum Engineering of Shaanxi Petroleum Society. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of Shaanxi Petroleum Society is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgement of IFEDC&IPPTC. Contact email: paper@ifedc.org or paper@ipptc.org.