Log Evaluation Of Reservoir Quality Differences Of P₂l In Jimusaer Sag

The object of this study is the Lucaogou Formation reservoir in Jimusaer Sag,mainly focus on"upper sweet spot"（P2l2²）and"lower sweet spot"（P2l1²）.Based on thin section,fluorescence thin section,Scanning Electron Microscope（SEM）and the test data of Mercury Injection Capillary Pressure（MICP）,constant-rate MICP and Nuclear Magnetic Resonance（NMR）,with the help of conventional log,image log,NMR log,lithoscanner and other well log data,the aim is to carry out a comprehensive study of reservoir characteristics and log evaluation of reservoir petrophysical parameters,based on which the difference of reservoir quality and the distribution pattern of sweet spot within single wells are evaluated.The results show that the mineral fraction of the Luchaogou Formation is dominated by terrigenous clastic minerals and carbonate minerals,clay minerals also developed.A lithological classification scheme for P2l2² and P2l1²suitable for log evaluation was established based on the mineral content difference,and the log response characteristics of seven typical lithologies,including dolomitic fine sandstone were summarized to realize the lithology identification of single wells.The thin section and SEM pictures reveal that the pore types of P2l2² and P2l1² are mainly secondary pores,developing intergranular dissolution pores and intragranular dissolution pores,etc.Clay mineral intergranular pores and organic matter pores are rarely seen.Fractures are mainly tectonic stress fractures,bedding fractures and abnormal high pressure fractures.Based on core-measured petrophysical tests,combined with the MICP and NMR data,the pore structure of P2l2² and P2l1²is divided into four types,from type I to IV change from remaining intergranular pores to intercrystalline pores and organic pores,and the FFV decreases.Combined with the petrophysical tests and rock electrical experiments,the log evaluation method of porosity,permeability and saturation of the P2l2² and P2l1² was established,and the parameter test confirmed a high degree of agreement.Based on the T2 spectrum of NMR log,the qualitative evaluation of the effective reservoir and fluid properties were achieved by combining the CMR-NG log data.By making the cross-plot of the FFV and T2LM,the well log identification of four types of pore structures in P2l2² and P2l1² was achieved.On this basis,based on the cross-plot of TCMR and So,three types of reservoir quality sweet spots and single-well evaluation were realized.Based on image log,the fracture types are mostly laminated fractures with some high-angle fractures.The fractures in the FMI images are mostly bedding fractures,and high-angle fractures are rare.Based on the orientation of the induced fracture and breakout,the present maximum horizontal principal stress direction is determined to be NE-SW,the logging evaluation of single-well fractability is realized.Based on the evaluation results of reservoir quality and fractability,it is considered that the lithology of Type I sweet spot is mainly silty fine sandstone and dolomitic siltstone,with good physical properties,NMR T2 spectrum has double peaks and the right side is higher;mainly intergranular pores,type I pore structure is developed and has good pore connectivity;the proportion of brittle minerals is relatively high,and sedimentary bedding and bedding fractures are often developed,which is easy for hydraulic fracturing,and the reservoir quality is the best.The results of the study can provide reference for the evaluation and production of effective reservoirs in P₂l₂² and P₂l₁².