Exploration for shale gas plays has proved economically viable in North America and has changed the way E&P companies address unconventional reservoirs. After Chinese governments drafted the 12th Five-Year Plan—an initiative designed to rebalance economics in various themes, including energy—gas shale exploration became a hot topic. Shale reservoirs comprise the source, seal, and the reservoir, and production is stimulated by hydraulic fracturing treatments. Modeling that predicts economic productivity and optimal fracture stimulation design is critically based on the detailed, integrated petrophysical evaluation for gas shale plays.
This paper presents an integrated approach to the petrophysical evaluation of resources in the Weiyuan field, the biggest gas shale play in China. Our approach integrates different types of data, including standard formation evaluation logs, geochemical logs and advanced acoustic logs. These data, when combined, provide answers about the reservoir quality and the completion quality. The reservoir quality is established by the information from conventional formation evaluation log and geochemical logs, which include TOC, mineralogy, porosity and gas in place etc. The completion quality is established by the analysis of advanced sonic measurement and resistivity image log, which include geomechanical parameters, natural fractures and induced fractures etc. In this new integrated petrophysical evaluation method, elemental capture spectrometry and advanced acoustic measurements are the keys for estimating reservoir and completion quality. Capture spectrometry measurements provide the accurate mineral content information that is important for ascertaining reservoir quality. Advanced acoustic data can provide the 3D geomechanical parameters and stress estimates required for fracture job design. After integrating reservoir and completion quality, the fracture design is optimized; components include outlining stages, perforation methods, intervals and fracturing fluids.
This integrated evaluation method is being used to establish the petrophysical and geomechanical properties of the Weiyuan gas shale target and also can be applied to other gas shales in China.