鄂西渝东地区页岩气井焖井时间优化研究——基于物质平衡与自吸耦合模型

Study on Optimization of Shut-In Time of Shale Gas Wells in Western Hubei and Eastern Chongqing —Based on Material Balance and Self-Priming Coupling Model

摘要: 焖井作业是页岩气井压裂后的关键环节，直接影响初期产能和经济效益。本研究以红星地区吴家坪组24口页岩气井为对象，针对目前焖井时间主要依靠经验值导致的优化不足问题，通过岩心自吸实验、微地震监测和生产数据分析，建立了基于“物质平衡法 + 自吸速率”的焖井时间优化方程。该方程综合考虑裂缝闭合、基质渗流和压裂液吸附三个阶段，采用牛顿–拉夫逊迭代法求解。研究显示：红星地区实际焖井时间平均23天，理论最优值为13.2~44.9天，平均34天；焖井时间与压裂液量、泥质含量呈正相关(R² = 0.42, 0.29)，与孔隙度呈负相关(R² = 0.24)；理论时间差与投产压力相关系数达0.71，验证了模型可靠性。建立了孔隙度–泥质含量和渗透率–液量快速计算图版，为现场应用提供了定量工具。

Abstract: Shut-in operation represents a critical phase following hydraulic fracturing in shale gas wells, exerting substantial influence on initial productivity and economic returns. This investigation focuses on 24 shale gas wells targeting the Wujiaping Formation in Hongxing area, addressing the limitation that current shut-in duration determination relies predominantly on empirical approaches lacking systematic optimization. Through integration of core spontaneous imbibition experiments, microseismic monitoring data, and production performance analysis, an optimization equation for shut-in duration was established based on the coupling of material balance principles and imbibition rate characterization. The proposed equation encompasses three governing stages—fracture closure, matrix fluid infiltration, and fracturing fluid adsorption—with solutions derived through Newton-Raphson iterative methodology. Results indicate that actual shut-in periods in Hongxing area average 23 days, whereas theoretical optimal values range from 13.2 to 44.9 days with a mean of 34 days. Correlation analysis reveals positive relationships between shut-in duration and both fracturing fluid volume (R² = 0.42) and clay content (R² = 0.29), while demonstrating negative correlation with porosity (R² = 0.24). The discrepancy between theoretical and actual shut-in durations exhibits a correlation coefficient of 0.71 with initial production pressure, validating model reliability. Practical calculation charts incorporating porosity-clay content and permeability-fluid volume relationships were developed, providing quantitative guidance for field implementation.