94 / 2023-07-13 16:52:39

川中-川西过渡带须家河组致密砂岩储层特征差异及优质储层形成机制

优质储层；主控因素；致密砂岩；须家河组；四川盆地

近年来，川中-川西过渡带简阳区块须家河组勘探取得新进展，包括须三下亚段、须四段和须五段在内多套储层取得突破，证实该领域具有较大勘探潜力。但整体研究程度较低，油气成藏基本地质条件研究比较薄弱，资源潜力不清。开展川中-川西过渡带核心建产区须家河组南部简阳区块与北部区块储层特征差异性对比分析、讨论不同区块优质储层的形成机制对于开展核心建产区下一步的须家河组油气勘探与井位论证具有实际意义。为明确川中-川西过渡带须家河组南部简阳地区和北部区块致密砂岩储层特征和主控因素，在须家河组新的分层格架下，结合铸体薄片、扫描电镜和物性分析等测试方法，针对川中-川西过渡带须家河组须三下亚段和须四段开展储层特征差异及优质储层形成机制研究。结果表明，川中-川西过渡带南部简阳区块和北部区块须家河组储层岩石类型均以长石岩屑砂岩、岩屑长石砂岩为主，南部区块储层砂岩石英含量在50%~60%，岩屑以变质岩屑+泥岩岩屑为主，成岩作用主要为压实作用、溶蚀作用钙质胶结和硅质胶结为主，储集空间主要为粒内溶孔，孔隙度峰值分布在6%~8%，渗透率峰值分布在0.01~1mD。北部区块石英含量在60%~70%，岩屑以硅质岩、浅变质岩岩屑和碳酸盐岩为主。成岩作用主要为压实作用、溶蚀作用和硅质胶结、钙质胶结、绿泥石胶结，储集空间主要为粒间孔和粒内溶孔，孔隙度峰值分布在4%~8%之间，渗透率峰值分布在0.01~10mD。优质储层形成机制结果表明水下分流河道微相、河口坝沉积微相、绿泥石胶结和溶蚀作用是研究区须家河组优质储层形成的关键。不同沉积微相物性统计表明研究区内河口坝储层物性与水下分流河道储层物性相当。压实作用是研究区主要的减孔作用，但简阳地区压实程度更高，这与简阳区块具有较高的塑性岩屑有关，塑性岩屑因压实作用挤压变形乃至形成假杂基而堵塞孔隙。溶蚀作用是研究区主要的增孔成岩作用，对于以次生溶孔为主要储集空间的南部简阳地区尤为重要。绿泥石胶结作用主要呈绿泥石包膜状，在抵抗压实的同时一定程度上抑制了粒间胶结物的生长，主要见于北部区块，南部简阳区块不发育，表明绿泥石的发育与岩石成分乃至物源有关。简阳地区须四段致密砂岩储层主控因素是沉积微相和溶蚀作用的发育；北部区块的主控因素是沉积微相和高刚性颗粒碎屑、绿泥石膜和溶蚀作用的发育。

Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China；3.Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China)

Abstract：In recent years, new progress has been made in the exploration of the Xujiahe Formation in the Jianyang area of the transitional zone between central and western Sichuan, and significant breakthroughs have been made in a number of reservoirs, including the lower Member of Xu3, the Xu4 Member and the Xu5 Member, which confirms that this area has great potential for hydrocarbon resource exploration. However, the overall research degree of the Xujiahe Formation in the study area is relatively low, the study of the basic geological conditions for hydrocarbon formation is relatively weak, and the resource potential is unclear, which restricts the further exploration and development deployment. Therefore, it is of practical significance to analyze the differences in reservoir characteristics between the southern Jianyang area and the northern area of the Xujiahe Formation in the core production area of the transitional zone between central and western Sichuan, and to discuss the mechanism of formation of high-quality reservoirs in different areas, in order to carry out the next step of oil and gas exploration in the Xujiahe Formation in the core production area, as well as to demonstrate the well location. In order to clarify the reservoir characteristics and main control factors of tight sandstone reservoirs in the southern Jianyang area and northern area of the Xujiahe Formation in the transitional zone between central and western Sichuan, under the new stratification framework of the Xujiahe Formation, combining with the test methods of thin-sections, scanning electron microscope (SEM) and physical property analysis, this study carried out the differences in reservoir characteristics and the formation mechanism of high-quality reservoirs in the lower Xu3 M. and Xu4 M. in the transitional zone between central and western Sichuan. The results show that the rock types of the reservoirs in the southern Jianyang area and northern area of the Xujiahe Formation in the transitional zone between central and western Sichuan are both dominated by feldspathic litharenite and lithic arkose, the quartz content of sandstone reservoir in the southern area is 50%~60%, and the rock fragments are dominated by metamorphic and mudstone rock fragments, and the diagenesis is dominated by compaction, dissolution, carbonate and quartz cementation, and the reservoir space is dominated by intra-granular dissolution pore, with the peak porosity distributed at 6%~8% and the peak permeability distributed at 0.01~1mD. The quartz content of sandstone reservoir in the southern area is 60%~70%, and the rock fragments are dominated by cherts, low-degree metamorphic and carbonate rock fragments, and the diagenesis is dominated by compaction, dissolution, carbonate, quartz, and chlorite cementation, and the reservoir space is dominated by intergranular and intra-granular dissolution pores, with the peak porosity distributed at 4%~8% and the peak permeability distributed at 0.01~10mD. The results of the formation mechanism of high-quality reservoirs show that the sedimentary microfacies of the underwater diversion channel and mouth bar, the chlorite cementation and dissolution are the keys to the formation of high-quality reservoirs of the Xujiahe Formation in the study area. The physical properties of different sedimentary microfacies show that the physical properties of the mouth bar reservoir in the study area are comparable to those of the underwater diversion channel reservoir. Compaction is the main pore reducing effect in the study area, but the degree of compaction is higher in the Jianyang area, which is related to the high content of plastic rock fragments, which are extruded and deformed due to compaction and even form false matrix to block the pore space. Dissolution is the main pore enhancing diagenesis in the study area, and it is especially important for the southern Jianyang area, where secondary dissolution pores are the main storage space. Chlorite cementation is mainly in the form of grain-coating chlorite, which inhibits the growth of intergranular cement to a certain extent while resisting compaction, and is mainly develop in the northern area, however, it has not been found in the southern Jianyang area, indicating that the development of chlorite is related to the composition of the rock and even provenance. The main controlling factors for the tight sandstone reservoirs in the Jianyang area are the development of sedimentary microfacies and dissolution; the main controlling factors for the northern area are the development of sedimentary microphase and high rigid granular debris, grain-coating chlorite and dissolution.

Key words: High-quality reservoirs; Main controlling factors; Tight gas sandstone; Xujiahe Formation; Sichuan Basin