Reservoir Characteristics Of The Lower Cretaceous Shahezi-Yingcheng Formation In Changling Fault Depression,Southern Songliao Basin

The Changling fault depression is located in the south of Songliao Basin and spreads in the direction of NNE.The overall fault depression area is about 7.3×10~3km~2.The developed strata in the fault depression period include the Lower Cretaceous Huoshiling Formation,Shahezi Formation,Yingcheng Formation and Denglouku Formation.In this paper,the Shahezi Formation and Yingcheng Formation are mainly used as the research objects,and the stratigraphic-tectonic lattice characteristics of the study area are analyzed by logging interpretation,3D seismic interpretation and test data analysis.According to core facies,logging facies and well-seismic comparison,the correspondence between seismic facies and lithofacies in the target layer in the study area was established,and the distribution characteristics of lithofacies were finally determined by combining rock type and sand-to-ground ratio.Through microscopic identification and test data analysis,the microscopic characteristics and physical properties of clastic rock and volcanic rock reservoirs were determined.Linear regression analysis and thickness weighting method were used to predict the porosity and permeability spread characteristics of clastic rock reservoirs in the Shahezi Formation and Yingcheng Formation.Finally,combined with the analysis of source rocks,the distribution characteristics of clastic rocks and the distribution characteristics of volcanic rocks,the development characteristics of favorable reservoirs in the study area were predicted.Well logging data and core data show that five lithofacies are mainly developed in the Shahezi Formation-Yingcheng Formation of Changling Fault depression,including lacustrine facies,braided river delta facies,fan delta facies,lake bottom fan facies and volcanic lithofacies,which can be further divided into 15 subfacies and 37 microfacies.During the Shahezi Formation period,the Changling Fault depression was a shallow lake-semi-deep lake-fan(braided river)delta sedimentary system dominated by lake sedimentation and developed semi-deep lacustrine facies.During the Yingcheng Formation period,the middle part of the fault was dominated by volcanic construction,the northern and southern shallow lakes developed,and the east and west sides developed fan(braided river)deltas,which was the shallow lake-fan(braided river)delta-volcano construction system.Through thin sections and scanning electron microscopy,it was observed that the Shahezi-Yingcheng Formation in the region developed two types of reservoirs,clastic rock and volcanic rock,the clastic rocks were mainly feldspar clastic sandstone and rock clastic sandstone,the structural maturity and composition maturity were low,and the volcanic rocks were mainly moderately acidic volcanic rocks.The reservoir mainly suffered from mechanical compaction,cementation,substitution and dissolution,and the pore development was mainly secondary dissolution pores and cracks,and the primary pores were few.The results of test data analysis showed that the clastic reservoirs of Shahezi Formation were mainly Class III.porosity and compactness,and the pore structures were Type IIIB and Type IIIA.The clastic reservoirs of Yingcheng Formation are mainly class I porosity and compactness,and the pore structure is mainly type IIIB and IIIA,followed by type IIB and II.A.The porosity of pyroclastic reservoirs was mainly class III.,and the permeability was mainly class V.The porosity of volcanic lava reservoir is mainly class V and class IV.,and the permeability rate is mainly class V.Lithology,lithofacies type and diagenesis are the main controlling factors of reservoir physical properties in Changling fault depression.The physical properties of coarse clastic rocks are better than those of fine clastic rocks,and the tuff in clastic rocks will reduce the physical properties of reservoirs,and volcanic breccia and mafic lava have the best physical properties in volcanic rocks.Among the clastic rocks,the underwater diverted channel and mat-shaped sand microfacies at the leading edge of the fan delta had the best physical properties,and the upper microfacies and cavitary accumulation microfacies reservoirs in volcanic rocks had the best performance.Mechanical compaction and dissolution formed a secondary pore high-value zone at a depth of about 3200～4000m.The superposition analysis shows that there are four favorable clastic reservoir areas in Shahezi Formation of Changling fault depression,which are the favorable clastic reservoir area in the west of Well Chashen 1,the favorable clastic reservoir area in the east of Shenzijing secondary fault-controlled depression,the favorable clastic reservoir area in the west of well Tuoshen 6 in Chaganhua fault concave,and the favorable clastic reservoir area in well Fu15 in the south concave of Fulongquan.There are two favorable clastic reservoir areas in Yingcheng Formation,the clastic reservoir areas near the controlling fault in the southeastern margin of Changling fault depression and the clastic reservoir areas in well Fu 14-Fu 26.There are three favorable volcanic reservoir areas in Yingcheng Formation,namely,the favorable volcanic dome reservoir area on the west side of well Chashen 1,the favorable volcanic dome reservoir area of well Changshen 101-Changshen 104 and the favorable volcanic dome reservoir area of well Yaoshen 6.