Abstract Pore pressures in the Xujiahe gas-bearing formations are highly overpressured in the western Sichuan basin. The abnormally high overpressure and strong tectonic stress cause very high horizontal stresses. The high in-situ stresses, tectonic stress regimes, and tight formations severely impact development and production of the Xujiahe tight sandstone reservoirs. Overpressure generation mechanisms are analyzed based on measured data in several dozen wells in the studied gas fields. It is found that the sonic or seismic transit time can be used to predict pore pressure. Two major reservoirs (Xu2 and Xu4) belong to different fluid compartments with distinct pore pressure gradients. The Xu4 has a much higher pore pressure gradient (20 MPa/km) than the Xu2 (15.6 MPa/km). Measured data from hydraulic fracturing tests and borehole image logs in vertical wells are analyzed. The results show that the minimum horizontal stress gradient in the Xu4 reservoir reaches as high as 24 MPa/km, close to the overburden gradient. The Xu2 reservoir has a slightly lower minimum horizontal stress gradient. The high minimum horizontal stress and high rock strength cause abnormally high formation breakdown pressure gradient (24.8–34 MPa/km). The high breakdown pressure, high propagation pressure, and unfavorable stress regime result in a great difficulty for the reservoir stimulation. One of the major impacts is that hydraulic fracturing operations can only create very short hydraulic fractures, which markedly limits reservoir productivity. Based on field measurements, in-situ stress determination and assessment are given, and a new method for horizontal stress estimation is proposed. Accordingly, reliable prediction of formation breakdown and propagation pressures are proposed, which are more suitable for the tight reservoirs. Recommendations are given for effective development of the tight reservoirs with impacts of high in-situ stresses.

中文翻译：

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地应力、异常孔隙压力及其对构造活动川西盆地三叠系须家河储层的影响

摘要 川西地区须家河含气地层孔隙压力处于高超压状态。异常高的超压和强烈的构造应力导致非常高的水平应力。高地应力、构造应力状态和致密地层严重影响须家河致密砂岩储层的开发和生产。根据所研究气田数十口井的实测数据，分析了超压产生机制。结果表明，声波或地震波传播时间可用于预测孔隙压力。两个主要储层（Xu2 和Xu4）属于不同的流体隔室，具有不同的孔隙压力梯度。Xu4 的孔隙压力梯度（20 MPa/km）比 Xu2（15.6 MPa/km）高得多。分析了来自水力压裂试验和垂直井井眼图像测井的测量数据。结果表明，徐4油藏最小水平应力梯度高达24 MPa/km，接近上覆岩层梯度。Xu2 储层的最小水平应力梯度略低。高最小水平应力和高岩石强度导致异常高的地层破裂压力梯度（24.8-34 MPa/km）。高击穿压力、高传播压力和不利的应力状态给储层改造带来了很大的困难。主要影响之一是水力压裂作业只能产生非常短的水力裂缝，这显着限制了油藏产能。在现场测量的基础上，给出了地应力的确定和评估，并提出了一种新的水平应力估计方法。因此，提出了更适合致密储层的地层破裂和传播压力的可靠预测。对受高地应力影响的致密储层的有效开发提出了建议。