Application of Imaging Logging Technology in Impact Factors and Effectivity of Fracture Development Evaluation in Keshen Area, Tarim Basin

The reservoirs of Bashijiqike Formation in Kuqa Depression Keshen area of Tarim Basin have a great depth. As a result of diagenesis and late stage structural transformation, reservoirs are characteristic of typical poor... [ view full abstract ]

The reservoirs of Bashijiqike Formation in Kuqa Depression Keshen area of Tarim Basin have a great depth. As a result of diagenesis and late stage structural transformation, reservoirs are characteristic of typical poor physical property which belong to fractured tight sandstone reservoirs, so that reservoirs fracture development characteristics directly impact oil and gas production capability. Fracture development influence factors and effectivity evaluation are important basis of reservoirs evaluation and exploration deployment.
This study based on 287.91m core analysis and 1853.3m imaging logging data took advantage of normal logging, X-ray and SEM analysis data; built up an "Interactive changing window length fine imaging logging interpretation method" under "Core-scale logging", and evaluated the effectivity of fracture combining array lateral logging and multipole sub shear wave logging on the basis of imaging logging fracture identification.
The results indicate that applying interpretation method of imaging logging under core scale using Geoframe software to qualitatively recognize the fractures, and calculate fractures quantitative parameters including fracture dip-angle, density, and minor fracture open degree in the study area, the main sandstone fractures type are structural fractures, which are mainly high-angle fractures, then inclined fractures. By analysis of elliptical hole characteristics on imaging logging images, long axis direction indicates the direction of minimal principle stress, so maximum principal stress direction in Keshen area is South-North; and the predominant fractures strike direction is close to S-N parallel to the maximum principal stress direction, which are important to reform the property of the low pore and low permeability reservoirs in this area. Comprehensive analysis shows that Cretaceous fractures in Keshen area forming in the same stage are effectively open, which are ideal storage and transportation space for oil and gas. Fracture development also controlled by lithology, reservoir heterogeneity and fluid pressure. After counting fracture parameters in different sedimentary microfacies, it can be concluded that fractures mainly develop in fine sandstone reservoirs, low porosity underwater distributary channel and mouth bar microfacies; within the same lithofacies, fracture development has a negative correlation with porosity.
Key words: tight sandstone; fracture effectivity; impact factors; imaging logging; Keshen gas field.