Quantitative fracture evaluation method based on core-image logging: A case study of Cretaceous Bashijiqike Formation in ks2 well area, Kuqa depression, Tarim Basin, NW China

Abstract

A quantitative evaluation method of fracture is established based on core observation and image logging, and is used to characterize the distribution feature of fractures in Bashijiqike Formation of ks2 well area. This method gets the empirical corrections of fracture parameters between cores and image logging in the same depth, and these empirical values will be used in other depth where cores are not acquired to obtain all the fracture parameters per meter of the target layer. The study shows the fractures in ks2 well area are mainly high angle structural fractures between 45°−75°, and their strikes are near SN or near EW. The fracture linear density values are 0.11−1.30/m, the fracture area ratio is 0.027%−0.130%, the average fracture width is 0.13−0.55 mm, and the fracture length is 0.39−1.20 m. The development of fracture is divided into three levels (I-developed, II – relatively developed, III-poorly developed) based on the linear density value and surface area ratio. Fractures in this well area are most abundant in sandstones of 1st and 2nd members of Bashijiqike Formation, forming 4-6 fracture segments with good continuity. The thicknesses, development levels, parameters of fracture segments decrease exponentially with the increase of distance to fault and to anticline axis. The most favorable area (I – II) is within 800 m from the fault, or within 1 800 m from the anticlinal axis. It is predicted the fractures in ks2 well area, are more developed in the eastern area than the middle-western area, and more developed in the southern area than the northern area, and that the linear fracture density can be up to 1.0/m around Well ks201, Well ks207-ks2-12, Well ks203 and areas near faults. Key words: quantitative fracture characterization, fracture development level, fracture distribution, image logging, Cretaceous Bashijiqike Formation, Kuqa depression, Tarim Basin