Abstract
Generating sufficiently complex fracture network is a prerequisite for horizontal shale gas wells to obtain industrial gas flow. Microseismic monitoring can visually represent the stimulated reservoir volume (SRV) and its dynamic process, which plays an important role in the adjustment of the pumping procedure and the fracturing design optimization for subsequent stages. In the meantime, worldwide study results show that the occurrence frequency of microseismic events has a positive correlation with the post-frac production. However, the relevance of the microseismic frequency with the geological and stimulation parameters, and what stimulation parameters and their combinations may encourage more microseismic events, are still key issues to explore. Shale gas production logging is a direct way to reflect the gas production contribution of individual stage/cluster, and it is also a measurement of fracturing success. Statistics show a fact about worldwide shale gas production logging tests: the major production contributions come from only about ⅓ stages/clusters. However, whether geological or engineering mechanism is the main control mechanism behind it, and what its correlation with the generated fractures is, are still unsolved.
This paper analyzes the microseismic data of 12 wells, and gas production logging data of 34 wells (for 5 wells among them, both microseismic and production logging data are available) in Jiaoshiba area, and statisticcaly analyzes geological (structure, zone, TOC, physical properties, brittleness, etc.) and engineering (stage/cluster length, fluid volume, proppant mass, pumping rate, etc.) parameters, and also the gas production effect. The results show that: (1) Stage/cluster production shows a good positive correlation with the occurrence frequency of microseismic events and SRV; (2) There is a significant correlation between the occurrence frequency of microseismic events and the pressure change in the treatment; (3) Contribution rates of gas production change little for different production systems and periods; (4) Stage/cluster contribution rates of gas production are significantly controlled by geological factors, whereas they have an undefined relevance with engineering parameters; (5) Contribution rates of gas production are greatly influenced by the flow pressure distribution along the horizontal wellbore.
Based on the above analysis and understanding, we have investigated the control factors of the microseismic frequency and gas contribution, and specially analyzed the relationship between typical treatment curve signature of pressure change and the production contribution profile plus microseismic frequency, presenting some advice on fracturing design optimization and treatment parameter adjustment for shale gas horizontal wells.
