Reservior Characteristics And Main Controlling Factors Of Quantou 4 Member Of Qian'an Area In Southern Songliao Basin

Qian'an area is located in the middle of Changling Sag at Central Depression in the south of Songliao Basin.It's a slope belt tilted towards the southwest in the region,which is one of the key areas of oil and gas exploration and development in Songliao Basin.Using core,well logging,oil testing data,based on fine straigraphic division and correlation and sedimentary microfacies,this paper focuses on Q₄ reservoir characteristics,regularities of distribution and the main control factors.Based on the research of Reservior characteristics and main controlling factors,a classification and evaluation model of reservoir is built,contributing to the predition of favorable reservoir development zone.The Member Q₄ of the study area is deposited in early transgression under stable sedimentation background.The source direction is mainly southwest and west.It experienced a rapid transformation from lacustrine delta plain to lacustrine delta front.Sedimentary effect determines that the sandstone types in Member Q₄ of the study area are mainly feldspathic lithic sandstone and lithic feldspathic sandstone with moderate-good grain separation,rounding edge-minor circle,grain support and line contact Lord;interstitial components mostly calcite cimentation and authigenic clay minerals.The pore fluid has undergone the evolution from basic to acid to basic with a diagenetic sequence of the middle diagenetic stage A and four types of diagenetic facies have been formed.Compaction and calcite cementation are main diagenetic factors leading to tight reservoir in the study area.The average porosity of Q₄ reservoir in the study area is 8.5%with an average permeability of 0.157×10^-3?m².The porosity is dominated by low porosity to ultra-low porosity and permeability is mainly ultra-low permeability.The distribution range of pore-throat radius was 0.02⁰.55?m,and the median pore-throat radius was mainly distributed in the range of 0.04⁰.32?m.The distribution of throat is mainly fine to ultra-fine,with a general sorting.Pore-throat sorting coefficient and pore is positively correlated to porosity and permeability,which is different from conventional reservoirs.Deposition,diagenesis and tectonism are the main factors affecting the reservoir quality.The sedimentary microfacies directly control the original physical properties of the reservoir.The?underwater?distributary channel microfacies is the most favorable facies belt.Compaction is the main factor leading to the densification of the reservoir with the primary porosity was reduced on average by 52.0%by compaction.The cementation and metasomatism also aggravate the densification of reservoirs with the primary porosity was reduced on average by 22.5%,while the later dissolution can improve the reservoir physical properties to a certain degree,contributing in an increase of porosity of 3.04%.Finally,on the basis of comprehensive parameters such as lithology,physical property,oiliness and rock brittleness,the evaluation parameter values are determined,and the reservoirs in Member Q₄ of the study area are divided into three grades,and the reservoirs of each sand group are integrated in evaluation.The prediction of favorable exploration area provides certain theoretical and practical value for the exploration of oil and gas in this area.