致密油藏直井体积压裂压力分析模型

摘要

致密储层基质和裂缝一般表现为强应力敏感性,同时由于储层的致密性,基质和裂缝经常会表现为非稳态窜流特征,影响井底压力曲线的形态和特征,进而影响解释结果.目前国内外尚缺少同时考虑应力敏感及非稳态窜流的井底压力分析模型.参考典型致密油藏体积压裂直井的微地震监测数据,设计体积压裂直井渗流物理模型,同时考虑应力敏感和非稳态窜流,建立体积压裂直井井底压力数学模型并求解,进而获得井底压力的双对数曲线特征.研究结果表明:应力敏感系数αD越大,压力导数曲线上翘幅度越大,压裂未改造区致密油径向流动阶段越不明显;非稳态窜流系数λm越小,窜流出现时间越晚,窜流阶段的下凹幅度越大,窜流渗流过程持续时间越长,压裂区域的裂缝径向渗流过程越弱.该井底压力分析模型应用表明,相较于未考虑应力敏感及非稳态窜流的模型,更能准确地确定压裂区域的半径及相关储层参数,提高致密油藏直井体积压裂相关参数的解释精度,故可推广到致密储层参数反演或试井解释分析中.%Strong stresssensitivity is generally presented for the matrix and fracture in tight reservoirs,and meanwhile due to the reservoir compactness,the un-steady crossflow is often characterized for the matrix and fracture,thus the configurations and features of the bottom-hole pressure curves and moreover the interpreted results are influenced.At present,there lacks the bottom-hole pressure analyzing model simultaneously considering the stress sensitivity and un-steady cross flow at home and abroad.Taking the micro-seismic monitored data of the typical SRV vertical wells in the oil reservoir as the references,the physical model was designed for the well flow,the stress sensitivity and un-steady cross flow was considered at the same time,the mathematical model of the bottom hole pressure for the SRV vertical well was established and resolved,thus the log-log characteristics of the bottom hole pressure were obtained.The study achievements show that the bigger the stress sensitivity coefficient is,the greater the pressure derivative slope will be,the weaker the radical flow of the tight oil in the unstimulated areawill be;the smaller the un-steady cross flow coefficient is,the later the crossflow will be,the more serious the concave amplitude of the cross-flow will be,the longer the duration of the crossflow process will be,the weaker the fracture radical flow in the stimulated area will be.Compared with the models without considering the stresssensitivity and pseudo-steady crossflow,the analyzing model of the bottom hole pressure can more accurately determine the stimulated radii and other related reservoir parameters,enhance the interpreted precision of the relative parameters to the SRV of the vertical well in the tight oil reservoir,so the model can be generalized to the parameter inversion and well test interpretation of the tight reservoir.