Apply new technologies to effectively tap the potential of old shale gas wells.

From November 23 to November 24, 2022, Zhang Guangda, Secretary of the Party Branch Committee of the Geophysical Exploration Institute, Chairman of the Board, and General Manager, led a team to conduct on-site inspections and carry out targeted research on key objectives for the post-pressure target-layer exploration and攻关 (key technology breakthrough) pilot project at the Changning H3 platform.

The Changning H3 platform, located in Gaoxian County, Yibin City, Sichuan Province, is a horizontal well platform targeting Longmaxi shale gas as its primary target formation. Since coming on stream in January 2015, the platform has demonstrated excellent overall gas production performance. Based on several years of experience with shale gas fracturing, we preliminarily conclude that there still remain untapped shale gas resources between the old wells' boreholes. To evaluate the remaining shale gas potential after fracturing and to promote the exploration and development of existing old production areas, there is an urgent need for an exploration technique capable of assessing the evolution of fracture networks following production from these old wells. Specifically, we need to identify and map the fracture distribution patterns through inter-well fracture monitoring, comprehensively evaluate the overall fracture network configuration, and then analyze the extent to which shale gas resources have been utilized. Therefore, entrusted by the client, our company has undertaken scientific and technological research using both holographic electromagnetic methods and wide-area electromagnetic methods to address this issue.

Currently, the well spacing in the H3 old well area is 500 meters. Whether to fully exploit these wells and whether it is feasible to increase well density for further exploitation both require detailed exploration and research. In this study, we employed a holographic electromagnetic exploration method to survey an area of 9×9 square kilometers within the platform’s operational zone. We also conducted three-dimensional imaging of the central 4×4 square kilometer region of the H3 platform and evaluated the fracture distribution following production from the H3 old wells. Additionally, we carried out wide-area, dense inter-well fracturing monitoring to track fracture propagation. After comprehensively assessing the fracture distribution, we will analyze the utilization status of shale gas resources and provide technical support for the next phase of deploying new fracturing wells between existing wells.

Based on a comprehensive analysis of previous geological, geophysical, drilling, and development data, the Geophysical Institute has established a targeted task force to conduct specialized analyses of existing issues. Over the past year, in collaboration with Central South University, the team has carried out intensive research and trials focused on three-dimensional processing and inversion of holographic electromagnetic data, preliminarily producing three-dimensional imaging results. The project team has carefully analyzed and discussed these results and concluded that, at present, the three-dimensional holographic electromagnetic data can roughly reflect the electrical property distribution characteristics between old wells after fracturing. However, there is still considerable room for improvement in the three-dimensional spatial electrical inversion, particularly in terms of vertical resolution, where further enhancements through frequency-domain improvements could be explored. At the same time, the current results can only generate horizontal slices at fixed vertical depths. Yet, shale gas horizontal wells are not entirely horizontal; the vertical depth difference between their AB targets is about 100 meters. Consequently, the horizontal slice maps cannot accurately depict the fracture propagation patterns in horizontal wells. Therefore, in the next phase of research, it will be necessary to further extract slice attributes along layer boundaries, specifically targeting the three-dimensional spatial information of horizontal wells, so as to more accurately reflect the fracture-reformation patterns following hydraulic fracturing and to better evaluate the remaining shale gas potential after fracturing.

The application of wide-area electromagnetic (WAE) technology for detecting low resistivity in shale gas target formations has become relatively mature. However, this is the first time that such technology has been used to map the electrical properties of target formations after hydraulic fracturing and to characterize the three-dimensional spatial distribution of fractures induced by fracking. In this focused research effort, we will conduct pilot tests covering field data acquisition, post-fracturing electrical inversion methods, and interpretation and analysis of resulting cross-sections. Furthermore, we will integrate these findings with those from holographic electromagnetic studies to comprehensively analyze and evaluate the fracture distribution patterns observed between wells, thereby providing technical support for the redevelopment of the H3 platform.

Executive Producer | Zhang Guangda
Reviewed by | Zou Zhongping
Editor-in-charge | Zhou Huiying
Text | Yang Yuning
Figure | H3 Platform Project Department
Editor | Wen Han