摘要：

川南寒武系筇竹寺组页岩气储层作为我国页岩气资源新的开发接替层系，其高地应力、强天然裂缝发育和显著井间干扰等特征，对新区生产平台水力压裂效果的评估优化构成了严峻挑战，而传统压裂监测方法在空间连续性、井间尺度表征和段间改造差异量化方面均存在局限，对超深层页岩储层中裂缝扩展、裂缝—邻井相互作用以及天然弱面沟通等复杂裂缝行为难以实现连续监测。本研究针对该区域某生产平台拉链式压裂改造开展邻井套内低频分布式声波传感光纤应变监测，得到两口压裂井共52个压裂段施工全过程应变率数据，系统分析了压裂裂缝扩展远场应变特征，建立了包含原始DAS数据质量控制、低频信息提取、应变率瀑布图与施工参数同步分析、裂缝到达时间统计、停泵响应分析以及累积应变改造程度评价的现场数据解释流程。研究结果表明本次监测结果具有“响应普遍、位置对应、模式复杂、前后差异”的总体特征；水力裂缝扩展呈现“多裂缝竞争扩展、垂直缝与倾斜缝并存和大规模层理缝沟通”3种主要模式；裂缝到达邻井的速度和停泵时刻应变响应特征与裂缝扩展特征存在相关性，裂缝平均扩展速度主要受局部地应力与天然裂缝条件、压裂井与监测井之间的高程差、前序裂缝沟通程度以及拉链式压裂造成的局部应力场改变的共同控制，停泵阶段的应变响应揭示了不同裂缝类型的闭合差异，以张开型垂直缝为主的压裂段停泵后通常出现明显应变反转，表明裂缝闭合相对充分，受层理缝沟通或剪切型弱面滑移影响的段落则多表现为拉应变缓慢衰减且难以完全反转，说明裂缝面可能存在残余张开或剪切错动。本文首次将压裂远场应变监测结果用于储层改造程度量化分析，对不同压裂段改造强度和改造范围实现了量化评价。本研究还展现了压裂过程中天然地震的监测结果和对压裂及监测效果的影响。本文为深层页岩气压裂设计优化、井间干扰风险识别及多井协同开发提供了基于实测数据的工程解释路径，并为后续裂缝参数反演与改造程度定量评价奠定了基础。

关键词: 超深页岩储层, 水力压裂, 光纤监测, 低频分布式声波传感, 储层改造

Abstract:

As a new strategic replacement for shale gas development in China, the Cambrian Qiongzhusi Formation shale gas reservoir in the Southern Sichuan Basin is characterized by great burial depth, high in-situ stress, well-developed natural fractures, and notable inter-well interference. These characteristics pose severe challenges to the evaluation and optimization of hydraulic fracturing performance in new production platforms. Meanwhile, conventional hydraulic-fracturing monitoring methods are limited in spatial continuity, inter-well-scale characterization, and quantitative evaluation of stage-to-stage stimulation differences, making it difficult to continuously monitor complex fracture behaviors such as fracture propagation, fracture-offset-well interaction, and communication with natural weak planes in ultra-deep shale reservoirs. Address these challenges, this study conducted cased-hole offset-well fiber-optic strain monitoring using low-frequency Distributed Acoustic Sensing (DAS) during zipper fracturing operations on a production pad in this area. Strain-rate data were acquired throughout the complete treatment process of 52 fracturing stages from two treatment wells, and the far-field strain-response characteristics associated with hydraulic-fracture propagation were systematically analyzed. A field-data interpretation workflow was established, including raw DAS data quality control, low-frequency information extraction, synchronized analysis of strain-rate waterfall plots and treatment parameters, fracture-arrival-time statistics, shut-in response analysis, and cumulative-strain-based evaluation of reservoir stimulation effectiveness. The results show that the monitoring responses are generally characterized by widespread response, clear depth correspondence, complex response patterns, and significant differences between earlier and later treatment stages. Hydraulic fracture propagation mainly exhibits three dominant modes: competitive propagation of multiple fractures, coexistence of vertical and inclined fractures, and large-scale communication with bedding-parallel fractures. The fracture propagation velocity toward the offset well and the strain response characteristics at shut-in are closely correlated with fracture propagation behavior. The average fracture propagation velocity is jointly controlled by local in-situ stress and natural fracture conditions, the vertical offset between the treatment well and the monitoring well, the degree of communication with previously created fractures, and local stress-field modification induced by zipper fracturing.The strain response during shut-in reveals differences in closure behavior among different fracture types. Fracturing stages dominated by opening-mode vertical fractures commonly exhibit obvious strain reversal after shut-in, indicating relatively sufficient fracture closure. In contrast, intervals affected by bedding-plane communication or shear slip along weak planes generally show slowly decaying tensile strain that is difficult to fully reverse, suggesting that residual fracture opening or shear displacement may remain on the fracture surfaces. This study pioneers the use of hydraulic-fracturing far-field strain monitoring results for quantitative evaluation of reservoir stimulation effectiveness, enabling quantitative assessment of stimulation intensity and the spatial extent of stimulation for different fracturing stages. Furthermore, it documents the monitoring of seismic events during operations and discusses their impact. The study provides a data-driven framework for optimizing fracturing design, mitigating well interference risks, and enabling collaborative development in deep shale reservoirs, while establishing a foundation for future fracture parameter inversion and quantitative evaluation.

Key words: ultra-deep shale reservoir, hydraulic fracturing, fiber optic, low frequency distributed acoustic sensing, reservoir stimulation effectiveness

中图分类号: 

• TE357.1

• TE13