Inspired by the North American experience and success, unconventional resource exploration in China is experiencing rapid growth, and many operators in different blocks in the Sichuan area are engaged in shale gas drilling and completion. Despite the declared commercial success, the consensus is that the experience of extracting shale gas in the Sichuan basin is very different from the experience in North America or anywhere else in the world. During the completion phases, geomechanics uncertainty, proppant placement challenges, unexpected casing deformation, and inconsistent production results remain challenges as the industry seeks to understand these complex reservoirs. The multidisciplinary integration and analysis of production, reservoir, geological, and completion data provide insight into the source and potential solutions to the challenges faced in the Sichuan basin.
In this study, we review, analyze, and synthesize a broad range of information and results including fracturing data, fracturing geometry measurements, casing deformation occurrence, production analysis, and material balance analysis.
Operational data from hundreds of fracturing stages were summarized to reveal the common observation that most Sichuan gas fracturing operations result in abnormally high shut-in pressure, potentially indicating horizontal or fissure-dominated fracture planes. In addition, fracture geometry measurements, including micro-seismic data and post-fracturing height measurement, indicate fracture height containment and mixed fracture planes. A specific case study suggests that casing deformation has its root in the mixed fracture planes.
The integration of the observations and analysis from different aspects generates a plausible explanation for the complexity that dominates performance in Sichuan shale gas. Based on its unique geology and geomechanics features, the mixture of vertical, horizontal, and fissure-dominant fractures is very likely inevitable for shale gas development in this basin, and the understanding of this specific complexity is a prerequisite for future planning of the field, drilling laterals, and proper choice of completion strategy and fracturing schemes.