Abstract: Current fracturing monitoring and interpretation technologies face difficulties in effectively explaining the parameters of the propped fracture network. This paper presents a method for interpreting the parameters of the propped fracture network based on pump-stopping pressure drop monitoring data. The dynamics of the bottom-hole pressure drop is simulated by a model established for the pressure drop during the pump-stopping phase in a single fracturing stage, which considers the coupling effects of the proppant transport within the primary and secondary fracture networks, fluid leak-off, and fracture network closure. On this basis, pressure drop characteristic curves are plotted for different propped fracture network widths and densities. This method aids in identifying the type of propped network and establishes a process for the inversion of propped network parameters. A typical shale gas well A, located in the Weiyuan Block of Sichuan Basin, is selected for the case study. The effectiveness of the proposed method is validated by comparing it with the monitoring results of optical fiber and tracer gas production profiles. The results further demonstrate that the sand-propped fracture volume is the primary control parameter for the post-fracturing productivity of shale gas wells. Then a comparison of the interpretation results for propped fracture network parameters from two completion techniques in a fracturing interval of Well A reveals that for the casing-cemented completion, the fracture network is characterized by short and narrow main fractures, as well as wide and dense secondary fractures; the sand-propped volume ratio is higher (77 % vs. 62 %). In contrast, for the non-casing-cemented completion, the fracture network is characterized by long and wide main fractures, as well as narrow and sparse secondary fractures; the fluid propped volume ratio is higher (38 % vs. 23 %). By fully utilizing the geological characteristics of well-developed natural fractures, a larger-scale modification effect can be achieved with a smaller construction scale, thereby maximizing risk prevention and control, cost reduction, and efficiency improvement. Research indicates that the proposed method requires only fracturing construction data and wellhead pressure monitoring data after pump-stopping to provide a comprehensive and quantitative evaluation of the six core parameters of the propped fracture network.

Key words: shale gas, fracturing monitoring, pump-stopping pressure drop, propped fracture, fracture network parameter interpretation, sand-propped fracture volume

摘要： 针对现有压裂监测解释技术无法对支撑缝网参数进行有效解释的难题,提出一套基于停泵压降监测数据的压裂支撑缝网参数解释方法。通过建立考虑支撑剂在主、次裂缝网中运移、缝网内液体滤失与支撑缝网闭合耦合效应的压裂段停泵压降模型模拟井底压降动态,绘制出不同支撑缝网宽度和密度下的压降特征曲线,从而诊断支撑缝网类型并建立支撑缝网参数反演计算流程。选取四川盆地威远区块典型页岩气A井开展应用,通过与光纤和示踪剂产气剖面监测结果对比验证了新方法的有效性,并进一步证明砂撑裂缝体积是页岩气井压后产能的主控参数。对比A井套管固井和未固井完井工艺下的压裂段支撑缝网参数解释结果发现,套管固井完井段压裂形成"主裂缝短窄、次裂缝宽密"型缝网,砂支撑体积占比更大,分别为77%和62%;套管未固井完井段压裂形成"主裂缝长宽、次裂缝窄疏"型缝网,液支撑体积占比更大,分别为38%和23%。充分借助天然裂缝发育的地质属性,可用较小施工规模实现更大规模的改造效果,实现"风险防控—降本提效"最大化。研究表明,新方法只需压裂施工数据和停泵后的井口压力监测数据,即可实现支撑缝网6个核心参数的定量评价。

关键词: 页岩气, 压裂监测, 停泵压降, 支撑裂缝, 缝网参数解释, 砂撑裂缝体积