渤东低凸起L3构造东营组含煤地层低渗储层特征及成因

渤东低凸起东营组储集层以低渗为特征,低渗成为制约该区东营组勘探的重要因素.通过多种分析测试方法,研究了渤东低凸起L3构造东营组低渗储集层特征,探讨了低渗储集层成因.L3构造东营组储集层砂岩溶蚀作用发育,斜长石含量低,碳酸盐胶结物含量低,高岭石含量高,石英加大明显.储集层主要以中孔低—特低渗为主,孔径小,连通差,吼道窄,排驱压力大.微量元素分析表明,研究区东营组沉积时为淡水环境;测井和岩心观察证实,地层中含多层碳质泥岩和煤层.早期腐殖酸的溶蚀作用,造成低温下不稳定的斜长石大量溶蚀,这些溶蚀孔隙在后期深埋过程中受压实和成岩作用影响被复杂化、细小化是储集层低渗的主要原因.早期碳酸盐胶结物少,岩石抗压实能力差也是储层低渗的重要原因.

Discussion on the Characteristics and Origin of Low-Permeability Reservoir of Coal-Bearing Strata in L3 Structure,Dongying Formation,Bodong Lower Uplift

The elastic reservoir of Dongying formation in Bodong Lower Uplift is characterized by low-permeability, which is a main factor influencing the exploration results. By using various analysis methods, the reservoir characteristics and mechanisms are studied in L3 structure, Dongying formation, Bodong Lower Uplift. The study results show that in the reservoirs ,the dissolution is strong, and the reservoirs are low in the content of plagioclase and the carbonate content, high in the content of kaolinite in clay minerals, with obvious quarts overgrowth in the reservoir of Dongying formation in L3 structure. The reservoir is basically medium porosity and low to very low permeability, which is characterized by small pore apertures, bad connectivity, narrow pore throat, and middle or high class of discharge pressure. Trace element analyzing results indicate that the sedimentary environment was freshwater when Dongying formation was deposited. It is confirmed by logging and core data that multilayer carbonaceous mudstone and coal exist in the formation. The dissolution of unstable plagioclase was formed in low temperature environment by humic acid in early stage. The dissolution pores was complicated and diminished by later compaction and diagenesis, which is the main reason for low permeability. The low content of early-stage carbonate cements result in low compressive strength is another important influencing factor.