The Synergistic Evaluation Of Reservoir And Analysis Of Developmental Control Factors In Fifth Member Of Majiagou Formation,Jingbian Gas Field

The Jingbian gas field is an ancient landform trap developed on the top of the paleoweathering crust of the Ordovician Majiagou Formation in the central Ordos Basin.Since it was discovered in June 1989,it has experienced more than 10 years of rapid exploration and high efficiency development stage,of which the cumulative exploration of gas reservoir in the Ma5₁₊₂ subsection is 2870.78×10⁸m³.The Ma51+2subsection is weathering crust reservoir.The pore is controlled by the sedimentary facies belt containing gypsum and karst landform.At present,most of the geological reserves in the original area of the gas field have been mobilized,and there are fewer areas for deployment.Therefore,it is very necessary to carry out the research on the expansion of the 5 member of Majiagou formation of the lower Ordovician.In this study,the stratigraphic contrast,the small layer reexamination and the sedimentary facies study are carried out in the Shanxi 330 well area based on the lithofacies and paleogeographic background,sedimentary environment and sedimentary strata characteristics of the Jingbian gas field.Furthermore,the core observation,the identification of thin slices and the analysis of the lithologic property of the rock samples were also conducted.The results shows:(1)The Ordovician weathering crust karst palaeogenomorphology in the study area can be divided into 4 types of geomorphologic units,such as the platform hill,the slope,the depression and the groove.Among them,the strata in the platform and slope area are well preserved,and the erosion and leaching are sufficient,which is favorable for oil and gas enrichment.(2)Jingbian Shan 330 well area can be divided into the mud cloud flat,the gypsum salt depression,the gypsum cloud flat,the Yun Ping,the ash flat and so on.Among them,the main gas reservoirs are Ma5₁₊₂ and the Ma5₄^1a,where anointed cloud flat and intertidal flat microfacies developed.The micro facies area containing gypsum cloud facies is favorable for the formation of gas field.(3)The diagenetic transformation in Shan 330 well area of Jingbian gas field is strong and the dense facies are widely distributed.The primary porosity of reservoir is low.The main pore type is dissolved secondary pore.The porosity are 0.6?10%,and the permeability are0.01?2×10^-3?m².(4)The Shan 330 well in Jingbian gas field is divided into 3 types of reservoirs.type I reservoirs are of great thickness,good physical properties,high permeability,crack development and high productivity;Type II reservoirs have relative larger thickness,good physical properties,medium permeability,mainly matrix,high gas saturation and great potential for development;Type III reservoirs are small in thickness,poor in physical properties,low in permeability,mainly in matrix,low in gas saturation and weak in production and construction potential.