Research On Sedimentary Microfacies And Sandbody Distribution Characteristics Of Shan 1 Member In Z1-L17 Well Area

The Z1-L17 well area is located in the southwest of the Ordos Basin and is a new block with a relatively low level of natural gas exploration and development in recent years.The 1st member of Shanxi Formation is an important potential development zone in this block.The predecessors had different understandings of the sedimentary facies of the first member of the block,and held the same viewpoints as fluvial facies,delta facies and beach bars.Due to the in-depth study of sedimentary facies in this area,the distribution of sand bodies is further unclear,which has severely restricted the exploration and development of natural gas in the study area.Therefore,it is necessary to conduct in-depth research on sedimentary facies and sand body distribution.Aiming at the above-mentioned problems in the study area,this paper makes full use of the geological data and drilling data of the study area to classify the strata of the Shan 1Member in the Z1-L17 well area,establish a stratigraphic framework,and carry out the deposition of the Shan 1 Member in the study area on this basis.Research on the distribution characteristics of sand bodies controlled by facies and facies.Finally,the comprehensive evaluation method of gray correlation degree is used to quantitatively predict favorable reservoir facies belts.The research gained the following knowledge:(1)The Shan 1 Member in the study area is divided into three sub-segments,Shan 1_3,Shan 1₂,and Shan 1₁ from bottom to top.The 8 stratigraphic correlation framework profiles covering the whole area reflect that the stratigraphic thickness of the three sub-segments is relatively stable.The average thickness of the stratum in the Shan 1₃ sub-segment is slightly larger than that of Shan 1₂ and Shan 1₁.The top structure of the three sub-segments reflects the better inheritance between the sub-segments and smaller structural fluctuations.(2)Delta facies and lacustrine facies are developed in the study area.Two subfacies of delta front and shallow lake are identified,seven types of microfacies are underwater distributary channel,distributary sand bar,distributary channel flanks,estuary bar,sheet sand,distributary bay,and shallow lake mud.The 4 sedimentary microfacies cross-section diagrams and sub-segment microfacies plane diagrams reflect the development of 2 to 3southwest-northeast underwater distributary channels in the study area.The scale of the underwater distributary channels in the Shan 1₃ sub-member is significantly larger than that of Shan 1₂ and Shan 1₁.(3)Controlled by the sedimentary microfacies,the study area mainly develops underwater distributary channel sand bodies,distributary sand bar sand bodies,estuary bar sand bodies and sheet sand bodies.The cross-sectional view of the contact relationship and connection status of the sand bodies and the plan view of the sub-segment sand bodies reflect that the distributary channel sand bodies are distributed in a southwest-northwest direction,and the distributary sand dam sand bodies are mainly distributed in the interior of the channel and the intersection of the secondary channels.The sand bodies of the Shan 1₃ sub-member have a wide development area,large thickness and good continuity,while the Shan 1₂ and Shan 1₁ sand bodies have small thickness and relatively poor continuity.(4)The distribution of sand bodies in the study area affects the distribution of gas reservoirs.Combining the physical property data of the reservoir,select 7 reservoir parameters including sand-to-land ratio,sand body thickness,porosity,permeability,saturation,effective sand thickness,and gas test results in the Shan 1₃ sub-member,and calculate the comprehensive evaluation of the study area using the gray correlation degree comprehensive evaluation method Index,which divides the reservoir facies into four levels:Among them,Type I and Type II are favorable reservoir facies belts for gas reservoirs in the study area,which can be the next development and deployment direction.