Study On The Formation Mechanism Of High-quality Reservoirs In The He 1 Member In The Hangjinqi Area Of The Ordos Basin

The reservoirs in He-1 Member of Lower Shihezi Formation in Hangjinqi area,northern Ordos Basin are deep buried.The divergence of eastern and western provenance are obvious,and types of diagenesis are diverse and the reservoir heterogeneity is strong.In recent years,with the development of the exploration process,the low porosity and permeability of the sandstone reservoir have become a hotspot.It is of great theoretical and practical significance to clarify the formation mechanism and its distribution law of the high quality reservoir in the He-1 Member reservoir in the Hangjinqi area.In this study,with tight-sandstone sedimentology and geology knowledge as a guide,referring to relevant literature and predecessors production report,collecting more than100 wells,observing more than 10 wells of core data,combind with microscope slice,SEM,X-ray diffraction,high pressure mercury,cathodoluminescence to research abouth the tight sandstone reservoir of He1 member qualitatively and quantitatively.I analysis granite composition,debris types and distribution,the pore structure and the type,the cementation sequence of various types of cements,dissolve types and strength and types and transformation of clay mineral in the whole study area.Through the mathematical statistics of high pressure mercury pressure data and nuclear magnetic resonance data,the macropores(>2 mu m),mesoporous(0.1 u m?2 mu m)and micropores(<0.1 mu m)are identified by high pressure mercury fractal dimension,and the average fractal degree of D1:2.984,D2:2.635 and D3:2.709 is calculated,and the fractal degree of macropores is the highest.The difference of feldspar content results in the East pore type of the study area mainly based on the dissolution of the feldspar grains,while the pore type in the western part of the study area is mainly intergranular dissolved pores.The grain size of the reservoir generally reaches the medium and coarse sand grade,even the gravel grade,the size of the grain size is well correlated with the pore permeability relation.The conglomerate and the gravel bearing coarse sand rock have better reservoir properties,and the better the sorting is better.The major Mega sandstone(>20 m)and large(>2 m)intergranular dissolved pores in the gravelly sandstone and coarse sandstone reservoirs are the main ones,which greatly influence the physical properties of the reservoir and increase the D1 value obviously.The diagenesis of the study area is complex,and the early calcite cementation and dissolution are favorable for the formation of high-quality reservoirs.According to pore formation and pore type,the reservoirs in the study area are divided into four types: the porosity of type ? reservoir is higher than 10%,formed of better connecting intergranular dissolution pores,or uneven large particle and intergranular area dissolved pores The porosity of types ? reservoirs is 7%?10%,which is made of sole intragranular dissolusived pores or cements partial dissolved pores;Type? reservoir' porosity is 4%?7%,mainly of isolated dissolution pore or intergranular microporous;Type ? reservoir porosity <4%,which is inefficient reservoir.The highquality reservoirs are mostly distributed in the high-energy river diara microfacies,and the Hangjinqi North and Hangjinqi East are favorable and high quality reservoir development zones.