Sandstone Diagenesis And Physical Property Characteristics From Yingcheng Formation Of Shiwu Oil Field In Lishu Fault Depression

The Shiwu Oil Field is located in the northern area of Lishu fault depression, thebasis of rich oil and gas combined with numerous sedimentary systems forms diversecombination traps, which makes good prospects for oil and gas. The exploration ofShiwu Oil Field before is mainly distributed in the shallow, with the deepening of theexploration degree, deep layer has been paid more attention. But in the process ofpractical work, the hydrocarbon potential of the area has not been excavated properly.Yingcheng Formation gets the attention of many scholars, as the good reservoir capassemblage in the deep of Lishu fault depressionBased on variety of technical methods such as polarizing microscope, castingthin sections, scanning electron microscope and X-ray diffraction, systematicpetrological, diagenesis and reservoir physical property characteristics of YingchengFormation sandstones were studied, combine with physical property characteristicsdata of sandstones. And also analyzed the factors which affecting the characteristics ofsandstone.Four groups of Yingcheng Formation (K1yc1、K1yc2、K1yc3、K1yc4) mainlydeveloped lithic arkose and feldspathic litharenite, and the clastic materials mainlyinclude quartz, feldspar and volcanic debris. General content of interstitial material isrelatively less, the cements is mainly calcareous cement and siliceous cement.Sandstones of Yingcheng Formation experienced complex diagenesis, strongmechanical compaction and pressure solution lead the particles closed packed,causing the intergranular pores are not developed. Intensive cementation, various ofcements, and the complex cementation stage seriously affected the pore characteristics of reservoir. Dissolution is mainly occurs on the edge and internal of feldspar anddebris, forming secondary pores, which have a positive effect on reservoir physicalproperty. Alteration also mainly appears in feldspar and debris, the alteration extent isgeneral low. After experiencing the complex diagenesis, the sandstones of YingchengFormation are in the A-B period of middle diagenesis stage.Pore types of reservoir sandstones of four groups of Yingcheng Formation areexpanded intergranular pore, intragranular dissolved pore and mould pore. Planeporosity of the sandstones is mainly low-grade, pore diameter is mainly a relativelysmall level pore, pore throat width is mainly medium throat level, which played animportant connection role in the reservoir. The type of reservoir belongs to low-ultralow porosity and ultra low-medium permeability, the central structural belt of thenorth of xiaowujiazi SN17-SN203-SN201-SN165-SW103-SW6area is the favorableblock.Mechanical compaction, pressure solution metasomatism and alteration havesignificant influence on the physical property characteristics of sandstone reservoir.The shallow sandstone is influenced by mechanical compaction, showing with theincrease of depth, the porosity and permeability decreased. The deep sandstone isinfluenced by dissolution, which formed secondary pores and maked the porosity andpermeability increased.