海相富有机质页岩储层压力预测方法——以涪陵页岩气田上奥陶统五峰组-下志留统龙马溪组页岩为例

Reservoir pressure prediction for marine organic-rich shale:A case study of the Upper Ordovician Wufeng-Lower Silurian Longmaxi shale in Fuling shale gas field,NE Sichuan Basin

页岩储层压力预测是评价页岩储层质量、认识页岩气富集机理、识别页岩含气性及寻找页岩气勘探有利区的基础。高-过成熟的海相富有机质页岩中发育大量纳米级有机质孔隙,且页岩储层普遍存在由生气造成的异常高压。目前页岩储层压力预测多建立在无机孔隙发育演化规律基础之上,没有考虑纳米级有机孔隙发育演化,从而导致“压力异常”的假象或者储层压力预测结果不准确。本文提出了一种适用于海相富有机质页岩的储层压力预测方法:假设页岩储层有机孔隙和异常压力共存,计算有机孔隙的声波测井响应,并校正声波测井曲线,建立新的压力预测模型。以涪陵页岩气田五峰组-龙马溪组页岩为例探讨了该方法的可靠性和实用性。结果表明,相校于原始Eaton法,该方法计算结果与实测压力数据吻合程度更高(R2=0.81),预测误差相对较小且符合正态分布。因此该压力预测方法能够有效、可靠地预测研究区海相页岩储层压力。据预测,焦石坝一期产建区地层压力总体具有背斜中间高、周缘低、东南侧局部具有高值的特征,该结果与无阻流量具有良好的相关性,进一步说明该方法的可靠性。该方法对于完善非常规页岩储层压力预测方法、推动超压页岩气勘探具有重要的现实意义。

The pressure prediction for shale reservoirs is essential for evaluating shale reservoir quality,understanding shale gas accumulation mechanism,identifying gas-bearing property and seeking favorable shale gas exploration areas.High-to-over-mature marine shale reservoirs rich in organic matters are commonly characterized by considerable nanoscale organic pores and abnormally high pressure caused by gas generation. At present,shale reservoir pressure prediction is practically based on the development and evolution of inorganic pores while ignoring the nano-scale organic pore growth,resulting in an illusion of“pressure anomaly”or inaccurate prediction of reservoir pressure. This study proposes a reservoir pressure prediction method for marine organic-rich shale. With the assumption that organic pores coexist with abnormal pressure in shale reservoirs,this method serves to calculate the acoustic logging responses of organic pores,correct the acoustic logging curve,and establish a new pressure prediction model. The new method is verified with Wufeng-Longmaxi shale reservoir in Fuling gas field as an example. Compared with the Eaton method,an original calculation method,the results of the revised method match well with the measured data(R2=0. 81). Also,the prediction error of the revised method is relatively small and in normal distribution,indicating that this method is suitable for the pressure prediction in the marine shale reservoir. The predicted pressure in Phase I Production Zone in Jiaoshiba area is generally characterized by high value in the center,low value in the surroundings,and locally high value in the southeast. These are well correlated with open flow capacity,further indicating the reliability of the method.It is of great practical significance to improving the unconventional shale reservoir pressure prediction and promoting the exploration in overpressured shale gas.