Glutenite, one of the most important petroleum reservoir rock in the Mahu Sag, is hard to break owing to its high heterogeneity, high abrasiveness and poor drill ability, and this has been a technical problem in petroleum engineering. As rock mechanics is the main factor affecting the breaking rock efficiency, the effect of external loading condition on the rock properties of glutenite need to be investigated. Up to date, there has been experimental research work on rock mechanics of the marine-deposit glutenite, but the counterpart research on continent-deposit glutenite is left undone. In this regard, the object of this study is to explore mechanical characteristics, of continent-deposit glutenite by performing laboratory experiments.

This study first discusses the strength of glutenite by triaxial compression tests under monotonic loading. Based on the results, rock mechanics properties (elastic modulus, internal friction angle, compressive strength and failure mode) are obtained. Then, a series of laboratory testing has been performed to assess the effects of cyclic loading and unloading response. Although the deformation characteristics and failure mechanism under cyclic loading are related to the monotonic loading, there is a significant difference between the two cases. Moreover, the influences of number of cycles, amplitude, and frequency are taken into account. Results from the cyclic loading tests indicate that glutenite has a “threshold value” of amplitude and an optimal frequency. Glutenite samples are weaker as the number of cycles increases.

This work is significantly important for the breaking rock efficiency enhancement of bit during drilling in glutenite reservior. It's the theoretical basis of putting forward bit and tool design method in the future.

1. Introduction

The drill ability of glutenite in the Mahu region of Junggar Basin is poor because of its strong heterogeneity and high grinding[Zhang 2017]. As to increase breaking rock efficiency and design a tool to increase ROP, the rock mechanics of glutenite under cyclic loading need to be study. During the last few decades, a lot of research has focused on the response of rocks under cyclic loading. The fatigue properties of rock materials have been found to be dependent on variables such as the amplitude, the upper limit stress, and frequency [Bagde 2005 and 2009, Xiao 2008]. It has also been reported that different materials show different responses when they are subjected to cyclic loading—some materials become stronger and more ductile, while others become weaker and more brittle [Bagde 2005].

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