M区块碳酸盐岩地层压力预测方法探讨

地层压力是钻井工程设计与施工的关键数据。碳酸盐岩地层压力形成机制不明确,没有考虑地层压力与体积弹性模量间的响应特征,导致目前根据欠压实理论和有效应力定律建立的预测模型不适用于预测碳酸盐岩地层压力。根据M地区碳酸盐岩所处的地质特征、地层类型、地层压力分布规律以及测井曲线等现场资料,分析了碳酸盐岩地层异常高压的特点;根据孔隙弹性理论,建立碳酸盐岩地层压力的预测模型,解释了裂缝型碳酸盐岩地层易产生异常高压的原因。研究结果表明,碳酸盐岩地层压力的大小取决于岩石体积弹性模量和地应力。该模型在M区块多口井进行了应用,预测精度达到90%以上,验证了该方法的可行性。

Discussion on Pore Pressure Prediction Method for Carbonate Rocks, M Block

The pore pressure is the key data for the drilling design and construction. The abnormal over-pressure generation mechanism of carbonate rocks is not known, the response characteristic of the pore pressure and the bulk modulus is not studied deeply, so the currently prediction models based on the under-compaction theory and the effective stress law is not suited to the pore pressure prediction of carbonate rocks. In this paper, base on the statistic of the real data such as the geological condition, strata types, pore pressure distribution and logging in carbonate rocks in M Region, it is revealed that the geological characteristic of the abnormal over-pressure in carbonate rocks. From the view of the pore elasticity theory, the pore pressure prediction model of carbonate rocks can be build; meanwhile, the generation mechanism of abnormal over-pressure in fractured carbonate rocks can be explained. The study shows that the control factors of abnormal over-pressure generation are the bulk modulus of the rock and in-situ stress. This new method is applied to carbonate rocks in M Block, Tarim Oilfield. The pore pressure prediction accuracy can reach 10% when compared to the measured data, demonstrating the promise of the proposed pore pressure prediction method.