辽河西部凹陷南段致密砂岩形成机理与原位覆压孔渗时空分布

The petrological characteristics，pore structures, porosity types as well as their causes and the diagenetic mechanisms of tight sandstones under abnormal low pressure environments will be studied，and the tight process and the tight time will be discussed by testing the homogenization temperature of the fluid inclusions in the carbonate cements and quartz overgrowths formed at different time in the tight sandstones of the southern part of West sag, Liaohe Depression, Bohai Bay Basin. The diagenetic framework will be built up and the diagenetic history of the tight sandstones will be modeled by using our own Diagenesis Numerical Model System V1.0. In-situ matrix permeability and porosity of many representative sandstones will be tested at different temperatures and pressures, and lots of the formerly measured data of permeability and porosity could be transformed into in-situ matrix permeability and porosity of corresponding depths. By considering various sedimentary and diagenesis factors'' influence on porosity and permeability, multivariate equations of higher degree about in-situ matrix permeability and porosity predicting models will be built up to predict the in-situ matrix permeability and porosity during hydrocarbon migration. Furthermore, the in-situ matrix permeability map will be imposed by a sand-thickness map and a structural map to predict the sweet points both in tight sand area and conventional reservoir area. Some new discoveries about diageneses of tight sandstones under abnormal low pressure environments and about the temporal-spatial distribution of in-situ permeability and porosity are being expected.

本项目拟研究辽河坳陷西部凹陷南段致密砂岩的岩石学特征、孔隙结构、孔隙类型及成因，探讨异常低压背景下的成岩机理，测试不同期次碳酸盐胶结物和石英加大边包裹体的均一温度，研究储层的致密进程和致密时间。应用成岩作用数值模拟系统V1.0，建立区域成岩格架，模拟成岩史。测试研究区具有代表性致密砂岩的原地覆压孔隙度和渗透率，将现有大量的实测孔隙度和渗透率转化为地下对应深度的原地孔隙度和渗透率。综合考虑各种沉积和成岩因素对储层孔隙度和渗透率的影响，确定致密砂岩的主控因素，建立多因素高次原地孔隙度和渗透率预测模型，预测油气运移时期的原地孔隙度和渗透率，叠合原地渗透率等值线图和储层等厚图、构造图，在致密砂岩分布区和常规储层分布区分别预测油气聚集的有利地区。本项目以期对异常低压背景下的成岩机理和地下原地孔隙度和渗透率的空间分布预测取得新进展，为致密砂岩油气的勘探奠定理论基础。

在渤海湾盆地辽河坳陷西部凹陷南段古近系的异常低压的致密砂岩中，发现了低产气流。然而，有关致密砂岩的成因机制、异常低压背景下的成岩机理和油气聚集规律尚不清楚，本项目对这些问题进行了研究与探讨。.本项目的主要研究内容为：①致密砂岩微观特征与成储机制；②异常低压背景下的成岩作用机理；③异常低压背景下成岩作用数值模拟与区域成岩格架建立；④孔隙度与渗透率的时空分布预测，成藏时间与致密进程的耦合关系；⑤有利勘探目标的确定。.在本项目的研究过程中，取得如下具有科学意义的重要研究成果：①辽河西部凹陷致密砂岩具有独特的形成环境：在致密砂岩发育段，发育地温梯度（28.5℃/km）、异常低压（压力系数0.5-0.9）、低矿化度(0.480 g/L～10mg/)、NaHCO3型水。②泥岩中的超压抑制了粘土矿物的转化、有机质的热演化和有机酸的生成与排放。低压或异常低压抑制砂岩的溶蚀作用，促进机械压实、碳酸盐胶结作用和硅质胶结作用，加速了储层的致密化。③古近系致密砂岩孔隙类型以次生孔隙为主，发育 “中孔-特低渗-微细喉-不均匀型”孔隙结构，属于次生型（成岩型）致密储层。④修订和完善了现行的成岩阶段划分标准，以生油高峰为界，将中成岩阶段A2亚期分为A21和A22两个微期，在A22有机质脱羧基本结束，溶蚀作用大大减弱，储层平均孔隙度<5%；⑤建立了异常低压背景下的成岩作用数值模拟系统；⑥定量研究了成岩作用和沉积对储层物性的影响，建立了异常低压背景下的预孔隙度和渗透率预测模型，预测了孔隙度和渗透率的时空分布，孔隙度预测误差小于2%。⑦模拟了砂岩的致密进程，分析了成藏时间与致密进程的耦合关系，预测了油气聚集的有利地区，新完钻的双兴1井发现了50多米厚的含油气层，孔隙度预测误差小于1%，证实了这种研究方法的合理性。