Novel idea of the theory and application of 3D volume fracturing for stimulation of shale gas reservoirs

Abstract

Shale gas has become a preferably alternative energy resource and national strategic goal for many countries for its noticeable advantages, including huge reserves and potentials, green, and broad distribution. Successful exploitation and utilization of shale gas has profoundly impacted global economy, regional politics, and even military strategies around the world. China holds the largest amount of recoverable shale gas reserves in the world. The shale gas recoverable reserves of China rank firstly in the world. However, most of the shale gas formations in China are low-permeability deposit and in conditions of geological complex, tectonic active, and lack of water, which makes the exploitation of shale gas difficult using the current methods. It is imperative to renovate the methods and techniques for stimulation of shale gas formations and to establish theory and technology for achieving high-efficiency exploitation and utilization of shale gas in China. This paper briefly reviews the adopted methods, principles, intractable issues and challenges in reservoir fracturing. A promising reservoir stimulation idea, i.e., 3D volume fracturing, and its principles and technology, are proposed. The volume fracturing of shale rock is defined as a three-dimensional fracturing process from the mechanics point of view, taking into account the interaction, growth, bifurcation between internal pores, inherent joints or cracks, and artificial fractures of reservoir rock under complex geostresses. The volume fracturing of shale rock is a failure process featured by large scale, multi cracking, high strength, and intensive energy release. The paper preliminarily frames the 3D volume fracturing theory from the aspects of 3D fracture modes, growth mechanism, interaction between artificial fractures and structural cracks, crack networks and development, loading type, modes and media for realizing large-scale volume fracturing, visualization of 3D fracturing process and computing programs, and stimulation implementation. Based on the early laboratory and field tests, we discussed the key scientific issues and technical challenges in realizing this promising stimulation technology for shale gas reservoirs.