基于权重分配的页岩气储层可压性评价新方法

为了解决现有页岩气储层可压性评价方法无法连续评价页岩气储层可压性的问题,考虑地质甜点和工程甜点双重因素,通过定量评价地质甜点参数,综合矿物组分含量、细观力学参数计算工程甜点参数,运用标准化、归一化、调和平均和算数平均方法建立了基于权重分配的页岩气储层可压性评价模型。该评价模型充分考虑了页岩储层含气性和易改造性的潜力,确定总有机碳含量、镜质体反射率、剪切模量和断裂韧度4个参数作为评价可压性的关键参数:当总有机碳含量大于2%、镜质体反射率大于1.3%、硅质矿物含量为20%~60%、碳酸盐岩矿物含量为10%~30%、黏土矿物含量为30%~50%时,页岩气储层最适合进行压裂改造。利用建立的评价模型评价了四川盆地威远地区某页岩气井W井储层段的可压性,并根据评价结果指导了该井的压裂设计与施工,压后微地震监测显示,产生了较多裂缝,实现了体积压裂。这表明,利用该评价模型可以连续评价储层的可压性,根据计算结果可以更加准确地划分有效压裂层段和遮挡层段,可操作性强,具有工程应用价值。 

A New Method of Fracability Evaluation of Shale Gas Reservoir Based on Weight Allocation

Existing shale gas reservoir fracability evaluation methods cannot be used in continuous fracability evaluation of reservoirs. After a quantitative evaluation of the parameters of geological sweet spots and the calculation of engineering parameters by combining the contents of mineral composition and the micromechanics parameters, a new shale gas reservoir fracability evaluation model based on weight allocation through standardization, normalization, harmonic averaging and arithmetic averaging methods was developed. This model considers the gas-bearing potential and stimulation potential of shale gas reservoirs, with four critical parameters (total organic carbon (TOC), vitrinite reflectance (Ro), shear modulus, and fracture toughness) defined for fracability evaluation which takes into consideration both geological and engineering criteria for sweet spots. It is proposed that shale gas reservoirs with TOC 2%, Ro 1.3%, silica mineral content of 20%-60%, carbonate mineral content of 10%-30%, and clay mineral content of 30%-50%, are good candidates for hydraulic fracturing. This model was used to evaluate the fracability of reservoir sections in Well W, a shale gas well in the Weiyuan area of the Sichuan Basin. Microseismic monitoring results showed that multiple fractures were generated during fracturing. This indicated that this model could be used in continuous fracability evaluation of shale reservoirs. From the calculated results, the pay zone and barriers could be identified accurately. So the proposed model is highly operable and worthy of engineering applications.