页岩气储层地层压力预测方法及其在四川盆地的应用

摘要

在构造稳定区,页岩气储层超压的成因以生烃增压为主,常规基于欠压实成因的地层压力预测方法并不适合直接应用于页岩气储层的地层压力预测.为此,以ClayPlus-Silt(CPS)模型为基础,考虑干酪根生烃的影响,基于岩石物理建模的思路,提出了一种新的正常压实速度趋势线构建方法,并结合Eaton方程形成新的页岩气储层地层压力预测模型.该模型能够更好地反映岩性变化对正常压实速度的影响,并且对实测压力数据的要求更低.基于该模型正演得到的正常压实速度,结合高精度叠后波阻抗反演,建立了页岩气储层地震地层压力预测技术流程.四川盆地某页岩气区块实际应用表明,该方法能有效提高页岩气储层钻前地层压力的预测精度.%Overpressure in tectonically stable regions of shale gas reservoirs is primarily caused by hydrocarbon generation.Conventional undercompaction-based methods are not applicable in these regions.Based on the Clay-Plus-Silt (CPS) model,along with the hydrocarbon effect,a normal compaction trend (NCT) was constructed using the rock physics modeling approach.The NCT was further combined with Eaton's equation to form a new pressure prediction model for shale reservoirs.This model can better reflect the influence of lithological change on normal compaction velocity with fewer measured pressure data.Combining the normal compaction velocity obtained by forward modeling,using the proposed model,with high-precision poststack impedance inversion,a seismic overpressure prediction workflow for shale gas reservoirs was constructed.Application results of this model from the Sichuan basin of China indicate its superiority in predicting predrill pore pressure.