文昌X油田珠海组低渗储层成岩作用与孔隙演化

Diagenesis and pore evolution of low permeability reservoir in Zhuhai Formation of Wenchang X oil field

文昌X油田是南海西部海域近几年新发现的低渗油田,目的层珠海组二段储层岩性变化大、局部胶结致密、非均质性强、成岩现象丰富、受成岩作用改造明显。文中根据铸体薄片、黏土矿物X衍射、碳氧同位素分析等实验资料,系统研究了文昌X油田珠海组二段低渗储层的岩石学特征、成岩作用特征及孔隙类型等,并在此基础上建立了基于成岩序列约束下的孔隙演化定量分析方法。研究结果表明:成岩作用控制孔隙演化过程,成岩早期机械压实作用是储层孔隙度降低的主要因素;早期碳酸盐胶结物对储层孔隙起保护作用;中成岩A期烃类注入导致酸性环境形成,长石等不稳定矿物大量溶蚀,储集空间得到极大改善;晚期碳酸盐胶结物对储层起破坏作用,储层孔隙度从38%降低为14%。该研究为文昌X油田下一步勘探开发提供地质依据。

Wenchang X is a newly discovered low permeability oil field in western South China Sea in recent years.The target stratum,the second member of Zhuhai Formation,has great reservoir lithology changes,tight local cementation,strong heterogeneity,abundant diagenetic phenomena,and obvious reservoir transformation by diagenesis.Basing on the analyzed data of cast sheet,X-ray diffraction of clay minerals and carbon and oxygen isotope analysis,the petrological characteristics,diagenesis,and pore type of the low permeability reservoirs in the second member of Zhuhai Formation are systematically elaborated.A quantitative analysis method of pore evolution based on diagenetic sequence is established.The results show that diagenesis controls pore evolution,and mechanical compaction is the main factor of porosity reduction in early stage while early carbonate cementation can protect reservoir pores.The accumulation of hydrocarbons in the middle diagenetic stage A leads to acidic environment and the dissolution of unstable minerals such as feldspar,which improves the reservoir space greatly.Late carbonate cementation destroys and weakens the reservoirs,and the porosity has been reduced from 38%to 14%.The research results provide geological basis for the exploration and development of Wenchang X oil field.