Sedimentary Characteristics And Sweet Spot Distribution Of The Lucaogou Formation In The Jimsar Depression

The Permian Lucaogou Formation in Jimsar Depression is rich in oil and gas reserves and has great exploration potential.In recent years,With the deepening of exploration and development,there is an urgent need to carry out research on the sedimentary characteristics of complex lithology and the development characteristics of"sweet spot"in the context of mixed sedimentation of saline lakes.Therefore,this paper takes the Middle Permian Lucaogou Formation in the Jimsar Depression as the research object,uses the data of drilling and logging,seismic and geochemical analysis and testing,carries out the stratigraphic classification and comparison and sedimentary environment analysis,clarifies the sedimentary characteristics of the Lucaogou Formation and the distribution law of the"sweet spot".The results show that:(1)The Lucaogou Formation is divided into P₂l₁ and P₂l₂ from bottom to top,P₂l₁can be divided into two sand groups P₂l₁² and P₂l₁¹,and P₂l₂ can be divided into two sand groups P₂l₂² and P₂l₂¹,and further the P₂l₁² sand group can be divided into seven minor layers and the P₂l₂² sand group can be divided into four minor layers,and this scheme can be reasonably compared between well profiles in the whole area.(2)The lake water body is deeper and water stratification is strong in the Lucaogou Formation period,and the overall environment is arid and hot,saline and reduced,mainly developing saline lake phase and delta phase,the early terrestrial clastic deltaic sedimentary system is more developed,and the late saline lake sedimentary system is more developed,and further identifies 10 kinds of sediments such as far sand dam,sheet sand,pre-delta mud,shallow lake mud,sandy flat,beach bar,mixed flat,dolomitic flat,deep lake mud and turbidity deposit.The paleoclimate,the intensity of material supply and the periodic rise and fall of the lake level control the stratigraphic development and sedimentary evolution of the Lucaogou Formation in the Jimsar Depression.(3)NMR porosity can be used as a sensitive parameter for"sweet spots"identification and"sweet spots"reservoir evaluation and classification,and NMR porosity above 5.5%can indicate"sweet spots".Seismically,the upper"sweet spots"is mainly characterized by low frequency and strong wave valley reflection,while the lower"sweet spots"is characterized by low frequency and medium to strong wave peak reflection.The wave impedance of the"sweet spots"differs greatly from that of the surrounding rock,so the application of wave impedance inversion can effectively predict the distribution of the"sweet spots".(4)The upper"sweet spots"is mainly distributed in the middle east of the depression,and the thickness trend is thickest in the center of the depression and gradually decreases toward the edge of the depression.The lower"sweet spots"is distributed in the whole depression,and the thickness trend is thick in the west and thin in the east,and thick in the south and thin in the north.