致密砂岩储层成岩过程中润湿性改变及其对油气运聚的影响-以松辽盆地南部白垩系泉四段为例

Reservoir study is the key element of tight sandstone oil and gas exploration and exploitation, while wettability alteration induced by diagenetic process is a weak link of this research, which constrains oil and gas distribution and profitable targets prediction. Taking tight sandstones of the Cretaceous Quantou formation fourth member (K1q4) in the southern Songliao basin as research objects, following research approach of combining micro and macro as well as combining qualitative and quantitative analysis, the key diagenetic mechanism will be analyzed and diagenetic evolution will be definite based on detailed characterization of diagenesis. Then, according to the differences of diagenesis types, authigenic minerals and pore fluid properties, both the reservoir wettability on macro- and micro-scale will be measured, and the controlling of diagenetic process on wettability alteration will be discussed, combining molecular dynamics simulation, the mechanism of wettability alteration by diagenetic process will be revealed. Based on the above, this project will analyze the oil occurrence characteristics within the tight sandstone reservoir, determine the chronological order of the main diagenetic events and oil charging, quantitatively analyze the relationship between oil saturation and the related authigenic minerals as well as the ion concentration, investigate the effect of wettability alteration on oil and gas migration, accumulation and distribution. Finally, the critical significance of wettability alteration to oil and gas accumulation during diagenetic evolution of tight sandstone reservoir will be summarized.

储层研究是实现致密砂岩油气高效勘探开发的关键，成岩过程对润湿性的改变是目前研究的薄弱环节，制约了油气分布规律和有利目标预测。本项目以松辽盆地南部白垩系泉头组四段致密砂岩为研究对象，遵循宏观与微观相结合、定性与定量相结合的研究思路，在成岩作用特征精细表征的基础上，分析关键成岩事件作用机理，明确储层成岩演化过程；依据成岩作用类型、成岩矿物特征及孔隙流体性质等差异，开展储层宏观尺度润湿性测试与微观孔隙尺度润湿性分析，探讨成岩过程对润湿性改变的控制因素，结合分子动力学模拟，揭示致密砂岩储层成岩过程对润湿性改变的作用机理；在此基础上，分析致密砂岩储层中原油赋存特征，确定各主要成岩事件发生时间与原油充注时间的先后顺序，定量统计含油饱和度与相关成岩矿物含量及不同类型离子浓度等之间的关系，探讨成岩过程中润湿性改变对油气运聚与分布的影响，总结致密砂岩储层成岩过程中润湿性改变在油气成藏中的重要意义。

储层研究是实现致密砂岩油气高效勘探开发的关键，成岩过程中润湿性的改变对油气分布具有重要的控制作用。本项目以松辽盆地南部白垩系泉头组四段致密砂岩为研究对象，综合运用岩心观察、薄片鉴定、QEMSEM分析、场发射扫描电镜分析、环境扫描电镜分析、流体包裹体分析、碳氧同位素测试、接触角测试、颗粒荧光分析以及数值模拟等技术方法，在致密砂岩岩石学和储集性能精细表征的基础上，结合储层成岩作用特征与演化研究，明确了成岩过程中储层润湿性改变机理，建立了成岩矿物与润湿性约束下的原油运聚与分布模式。致密砂岩岩石类型主要为岩屑长石砂岩和长石岩屑砂岩，成分成熟度低，结构成熟度中等。储层物性差，原生孔隙与次生孔隙并存，含粘土矿物晶间微孔，含油饱和度低，含油饱和度与储层物性之间无明显的相关关系。储层中石英胶结物与碳酸盐胶结物发育，长石颗粒溶蚀现象普遍，自生粘土矿物充填作用较强；蒙脱石向伊利石转化和石英颗粒间的压溶作用为石英胶结物的形成提供了主要的内源物质；碳酸盐胶结物的形成主要受有泥岩中机质脱羧作用影响，外源铁方解石在砂体边缘形成了致密胶结层，远离泥岩的厚层砂体中部储层中碳酸盐胶结物含量较少；根据自生矿物之间的交代切割与溶解充填关系，结合储层胶结-溶解作用机理分析，遵循成岩转化过程中的物质平衡原理，建立了松辽盆地南部白垩系泉四段扶余油层致密砂岩储层的成岩演化序列。致密砂岩成岩演化过程中碳酸盐胶结物与自生绿泥石的形成，是储层中部分孔喉向亲油性转变并形成混合润湿性特征的主要原因。储层中碳酸盐胶结物含量约为4%-5%的部位，最容易发生油气聚集，形成含油饱和度高值区；片状富铁自生绿泥石存在的孔喉表面亲油性好，原油沿半径较大的孔喉进入储层之后，易向自生绿泥石含量较高的亲油性孔喉中发生优势聚集。储层孔隙流体矿化度越大，钙和镁等二价离子含量越高时，越容易吸引原油分子形成离子对，在亲水性孔喉表面发生共吸附，促进油气在致密砂岩储层中聚集。