Analysis Of Hydrocarbon Accumulation Regularity Of Fault Layer In The Qianbei-Shenzijing Fault Concave Of Changling Fault Depression In Southern Songliao Basin

Qianbei-Shenzijing fault concave is located in the mid-north of Changling fault concave in the central depression area of Songliao Basin.The fault concave area is about 2.5×10³km²,the maximum thickness of the stratum is 4600m,and the maximum buried depth is 8700m.During the fault concave,the developed strata are Huoshiling Formation,Shahezi Formation and Yingcheng Formation.Combined with seismic interpretation and core and test data,the characteristics of fault concave structure and tectonic evolution in the study area were analyzed,and the corresponding relationship between seismic facies and lithofacies in the study area was summarized according to the comparison of well seismic.Furthermore,the distribution of sedimentary facies was determined based on the characteristics of equal seismic distribution of sand body to that of rock type.Based on the analysis of source,reservoir and cap,the main controlling factors of hydrocarbon accumulation are analyzed,the hydrocarbon accumulation law is established and favorable targets are predicted.The analysis of core facies and single well facies shows that there are 5 facies,15subfacies and 37 microfacies,including lacustrine,braided river delta,fan delta,sublacustrine fan and volcanic rock in Qianbei-Shenzijing Fault concave.In addition,45 types of seismic facies have been identified in Huoshiling formation-Yingcheng Formation in the study area,and the corresponding relationship between seismic facies and lithofacies has been summarized.Furthermore,it reveals the overall lithofacies palaeogeography of Huoshiling period,which is dominated by sheet outburst subfacies and sheet overflow subfacies,and partially developed shore and shallow lakes and fan delta.The lacustrine-fan（braided river）delta system in Shahezi period was mainly lacustrine deposition and developed in semi-deep lacustrine facies.The lithofacies palaeogeography features of Yingcheng period are mainly volcanic construction in the south and shallow lake in the north,and coastal and shallow lake and braided river（fan）delta are developed locally.The test and analysis of source rocks show that Shahezi Formation is the main source rock in the area,while Yingcheng Formation and Huoshiling Formation are secondary source rocks.Among them,Shahezi Formation of Shenzijing sub sag is the medium～good～best source rock.The source rocks of Shahezi Formation in Qianbei sub sag belong to good～best source rocks.The source rocks of Huoshiling and Yingcheng Formations are mainly poor to medium source rocks.There are two types of terrigenous clastic and volcanic reservoirs in Huoshiling Formation-Yingcheng Formation.Among them,Yingcheng Formation has the best physical properties,and its volcanic clastic porosity is mainlyⅤandⅢ,and permeability is mainlyⅣ～Ⅴ.The porosity of lava is mainlyⅤandⅢ,and the permeability is mainlyⅤ.The porosity of clastic reservoir is mainly of classⅡ,and the permeability is dense.The main reservoirs of Shahezi Formation are clastic rocks with relatively poor physical properties.The porosity is mainlyⅢ,and the permeability is mainly dense.There are three types of source-reservoir-cap assemblages in fault depression:self-generating and self-storing,up-generating and down-storing,down-generating and up-storing.CO₂ gas reservoir is mainly developed in the main control fault zone in the study area.The main control fault depression and its gentle slope edge uplift area are favorable for hydrocarbon gas reservoir development.Volcanic dome reservoirs are mainly distributed in the main depression and its adjacent secondary uplift area.Updip pinch-out lithologic reservoirs are mainly distributed in the edge of steep slope and gentle slope on both sides of main control depression.Lenticular lithologic reservoirs are mainly distributed in the middle of the main fault depression.Lithology-fault and fault-back reservoirs are mainly distributed in the transition zone between secondary uplift and fault depression.Based on the sedimentary,structural,source-reservoier-cap assemblage and other geological conditions,five favorable targets are found in the study area.The dip-out sand body in the Northern Slope break zone of Changshen 107 well,the anticline in the southern part of Changshen 107 well,and the volcanic dome in the southern part of Changshen 102 well are classⅠfavorable reservoir forming targets.The volcanic dome in the northern part of Chashen 1 well and the volcanic dome in Changshen 5 well and Qiantan 2 well in the western part of Changshen 5 well are favorable reservoir forming targets of classⅡ.The preferred exploration target in the future is the southern anticline of Changshen 107 well.