Study on formation conditions of high-quality reservoir of Sinian Dengying Formation in central Sichuan
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摘要: 为了弄清川中地区震旦系灯影组优质储层的形成条件,为该区油气的后期勘探和开发布署提供理论支持。以岩心观察、铸体薄片观察、地球化学测试资料、钻井资料和测井资料等生产测试资料为基础,对优质储层的形成条件进行综合分析,发现储集空间是由次生的孔、洞和缝组成,其中,沿藻纹层分布的溶孔、溶洞和溶缝是优质储层。研究表明优质储层是在沉积、成岩和构造共同作用下形成的,藻坪微相是基础,桐湾构造运动提供了必要的有利条件,表生岩溶作用是储层形成的关键。Abstract:
Central Sichuan is located at the eastern high point of the Leshan-Longnvsi ancient uplift axis. With a large amount of oil and gas resources, the Sinian Dengying Formation has a good exploration prospect. Since 2011 when CNPC deployed Well GS1 to explore Dengying Formation in the study area and then succeeded in discovering the oil and gas reservoirs, many scholars have done much research in this area and achieved a lot. But their opinions are similar only in terms of the understanding of lithology. In fact, multiple tectonic movements, the variable diagenetic environment and complex diagenesis of the Dengying Formation make it difficult for scholars to study the formation conditions of high-quality reservoirs in the Dengying Formation of the study area, which has resulted in a great controversy about the formation conditions of high-quality reservoirs. Therefore, taking the existing drilling cores and field profiles in central Sichuan and its adjacent areas as the main research objects, we studied the formation conditions of high-quality reservoirs in this paper, based on previous research as well as the testing data such as data from surveying wells and logging, and geochemical and physical properties. In this study, the existing drilling cores, field sections and rock slices in central Sichuan and its adjacent areas were analyzed for research of the rock types and reservoir space that constitute the reservoir. The results show that the lithology of Dengying Formation is mainly dolomite, with a small amount of mudstone and siliceous rock. There are many types of rock forming the reservoir, mainly including crystalline dolomite, sandy dolomite, algal laminated dolomite and karst breccia. The reservoir space is mainly composed of secondary pores, holes and fractures. The pores mainly include intercrystalline pores, intercrystalline dissolution pores, intergranular dissolution pores and residual intergranular pores. Among them intercrystalline pores and intercrystalline dissolution pores are mainly distributed in crystalline dolomite. In some parts, these two types of pores will be eroded and then expand into pore-type karst caves after karstification. However, intergranular dissolution pores and residual intergranular pores are mainly distributed in sandy dolomite, and the connectivity between them is poor. The caves mainly include "grape lace" caves, inter-gravel caves, and pore-type karst caves. The types of caves also include karst pores, caves and fissures that are distributed along the algal laminae. Among these caves, "grape lace" caves and inter-gravel caves are mainly distributed in breccia. Most of these two types of caves are filled with very small residual space. Pore-type karst caves are mainly distributed in crystalline dolomite. However, the dissolution pores, caves and fissures extending along the algal laminae are mainly distributed in the algal laminated dolomite. They are less affected by the later diagenesis and have weak infilling capacity, relative completeness and good connectivity. Fractures are mainly formed in a large number by tectonism and generally regarded as seepage channels rather than reservoir space for oil and gas. Finally, the existing research and comparison of the physical property different reservoir space show that the high-quality reservoir is composed of dissolution pores, caves and fractures distributed along the algal layer. The comprehensive study of the geological background of the study area indicates that the sedimentary facies of the study area are platforms. The subfacies are shallow water platforms and semi-deep water platforms, and the microfacies are shoal patches, cohesive shoals, algal flats, dolomitic flats and mud flats. At the same time, the correlation between lithology, reservoir space and sedimentary microfacies has been studied, showing that algal flats are the basis of high-quality reservoir development. The formation of reservoirs in Dengying Formation is mainly under the effect of recrystallization and karstification. Recrystallization can only improve the permeability of the reservoir, but cannot increase the effective reservoir space. Karstification took place during syngenetic-quasisyngenetic stage, supergene stage and buried-rock stage. In the syngenetic-quasisyngenetic stage, karstification mainly formed selective karst pores and caves, but rarely remained. Karstification in the supergene stage mainly formed karst pores, caves and fractures distributed along the algal laminae, which provided high-quality reservoir space. Buried karstification mainly occurred in the process of generation and degradation of oil and gas, and the overall transformation degree is small, but the connectivity and permeability of the reservoir space were improved. Therefore, supergene karstification plays a key role in the formation of high-quality reservoirs. In the study area, high-quality reservoirs are formed under the joint action of sedimentation, diagenesis and tectonism. According to the formation process of high-quality reservoirs, different periods and different pore structure characteristics, their evolution process can be divided into five parts: sedimentary period, shallow-burial period, supergene period, medium-deep burial period and period showing current characteristics. The study on evolution characteristics of high-quality reservoirs in different periods show that algal flats are the foundation for the formation of high-quality reservoirs; the Tongwan tectonic movement provides necessary conditions; supergene karstification is the key. -
Key words:
- central Sichuan /
- Sinian /
- Dengying Formation /
- high-quality reservoir /
- forming conditions
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图 2 川中地区震旦系灯影组中储层的岩石类型与储集空间类型
a. 晶粒(泥晶)白云岩,发育晶间孔, MX8井,5 290.00 m,×5(-) b. 晶粒(细晶)白云岩,发育晶间溶孔,AP1井,5 036.33 m,×5 (-) c. 沙屑白云岩,发育粒间溶孔与粒间孔,MX8井,5 309.00 m,×5(-) d. 藻叠层白云岩,发育沿藻纹层分布的溶孔、溶洞和溶缝,MX8井,5 114.54 m e. 角砾岩,发育砾间洞,Z6井,3 711.08 m f. 角砾岩,发育 “葡萄花边”洞,Z6井,3 733.20 m g. 粉晶云岩,发育孔隙型溶洞,GS2井,5 389.09 m h. 裂缝,MX8井,5112.05 m
Figure 2. The reservoir rock types and reservoir space types of Sinian Dengying Formation in central Sichuan
a. Crystalline (micrite) dolomite develops intercrystalline pores, MX8 well, 5,290.00 m,×5(-) b. Crystalline (fine crystalline) dolomite develops intercrystalline dissolution pores, AP1 well, 5,036.33 m, ×5 (-) c. Sandy dolomite develops intergranular dissolution pores and intergranular pores, MX8 well, 5,309.00 m,×5(-) d. algal laminated dolomite develops karst pores, caves and fissures that are distributed along the algal laminae, MX8 well, 5,114.54 m e. Breccia develops inter-gravel caves, Z6 well, 3,711.08 m f. Breccia develops "grape lace" caves, Z6 well, 3,733.20 m g. Powder crystal dolomite develops pore-type karst caves, GS2 well, 5,389.09 m h. Fissure, MX8 well, 5,112.05 m 5,112.05 m
图 6 砾间洞、溶沟和溶逢的充填特征及有机酸对孔隙空间的溶蚀改造特征
a- 砾间洞被上覆的沉积产物充填,AP1丼,5 035.90 m b- 溶沟被上覆的沉积产物充填,GS1丼,4 980.10 m c- 溶缝被渗流粉沙充填,GS1丼,4 906.60 m d-有机酸沿孔隙空间的溶蚀,Z4丼,4491.33 m
Figure 6. Infilling characteristics of intergranular cavity, dissolution ditch and dissolution fracture and the characteristics of corrosion transformation of organic acid on pore space
a- Inter-gravel caves are filled with overlying sedimentary product, AP1 well, 5,035.90 m b- Dissolution ditches are filled with overlying sedimentary product, GS1 well, 4,980.10 m c- Fissures are filled with seepage silty sand, GS1 well, 4,906.60 m d- Corrosion of organic acid on pore space, Z4 well, 4,491.33 m
表 1 川中地区灯影组沉积微相、沉积微相中的岩性特征和储集空间类型关系表(据周正[9])
Table 1. Division of sedimentary facies of Dengying Formation, lithologic characteristics and reservoir space types of different sedimentary microfacies in central Sichuan (According to ZHOU Zheng modified[9])
储集空间类型 岩性 微相 亚相 沉积相 粒间(溶)孔 砂(砾)屑云岩 点滩 浅水台坪 台坪 储集空间不发育 颗粒粘连白云岩 粘连滩 顺藻纹层方向的
溶孔、溶洞和溶缝藻叠层白云岩 藻坪 晶间孔和晶间溶孔 晶粒白云岩 云坪 半深水台坪 储集空间不发育 硅质岩,泥岩 泥坪 表 3 川中地区灯影组白云岩中锶、碳和氧同位素和有序度特征
Table 3. Characteristics of strontium, carbon and oxygen isotopes and ordering degree of dolostones from Dengying Formation in central Sichuan
样品编号 岩性 87Sr/86Sr δ18C/‰ δ18O/‰ 有序度 1 泥晶白云岩 0.708 58 −0.151 −8.221 0.503 1 2 粉晶白云岩 — −0.413 −7.458 0.646 7 3 粉晶白云岩 0.708 89 1.501 −7.825 — 4 细粉晶白云岩 0.708 92 0.315 −7.559 0.705 2 5 细粉晶白云岩 — 0.156 −7.608 — 6 细晶白云岩 — 0.465 −7.873 — 7 细晶白云岩 0.708 97 0.446 −7.878 0.867 3 8 溶缝渗流豆
(白云石)— 0.091 −8.718 — 9 溶缝渗流豆
(白云石)— −1.309 −9.869 — -
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