Abstract

The Weiyuan-Changning shale gas play is one of the most prolific exploration and development targets in China. This paper discusses a case study from a southern Sichuan shale gas field, expanding on the challenges encountered during exploitation of this reservoir, such as complex stratigraphy. Solutions are proposed based on examples of successful microseismic data application, highlighting potential necessary considerations when making project design decisions in such complex geological zones, such as the southern Sichuan basin.

Located in the southern Sichuan basin at the intersection of two major anticlines, the primary pay zone within the Changning is the Longmaxi. Because hydraulic fracture stimulation in this complex stratigraphy can be technically challenging, determining the created fracture geometries is crucial to evaluating the effectiveness of a stimulation application. Downhole microseismic fracture mapping was identified early during the development of this play as a solution to understanding the mechanics and results of subsurface stimulation. This technology was used to evaluate the hydraulic fracturing of three Ning201 horizontal gas wells in the Longmaxi.

Microseismic data acquisition in the Changning shale proved to be successful, as microseisms were detected at distances in excess of 1800 m from the Ning201 fracture treatments. Based on these data, a large fault to the west of the treatment wells significantly influenced fracture geometry, though not to the extent expected. However, crosscutting minor natural fractures that were activated during injection might have led to casing failure in one of the wells. These fractures, particularly natural fractures running parallel to the direction of maximum principal stress, should be considered when making project design decisions in complex geological zones, such as the southern Sichuan basin.

This paper provides an integrated analysis of a Changning hydraulic fracturing project based on microseismic data, previous completions in the area, and new information. This knowledge can be applied to help optimize future development of the Changning.

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