A New Logging Recognition Method of Small Fracture-Cave and Fills in Fracture-Cavity Reservoirs in Tahe Oilfield, Tarim Basin, China

Fei, Tian¹; Qiang, Jin¹; Yang, Li²; Hong-fang, Zhang²; Wen-bo, Zhang¹
¹China universtiy of petroleum, Qingdao, China.
²China Petroleum & Chemical Corporation, Beijing, China.

The carbonate reservoirs in Tarim Basin are characterized by low matrix-porosity, heterogeneity and anisotropy, where paleokarst derived fractures and caves are the main storage space. Fracture-cave contains a cave and genetical related fractures. Big fracture-cave can be recognized by drilling, seismic and logging data, but small fracture-cave (diameter less than 0.5m) which is also important hydrocarbon storage space and seepage channel in fracture-cavity reservoir can only be recognized in outcrops, core and image logging data. However, the recognition of small fracture-cave is very difficult in wells where the core and image logging data is absent, which seriously blocks the overall study of fracture-cavity reservoirs and accurate reservoir geological models building.

First, we demarcate conventional logging data from core and image logging information; then five cave-sensitive parameters and three fracture-sensitive parameters are chosed, which are weighted by normalization and weighted method; third, we build a recognition function for fractures and caves respectively, and indentify the threshold values, whose recognition rates are over 81% compared with the result from core and image logging. We use DEN-SH, RD-SH cross plot method to recognize types of fills which conclude sediments, breccias and chemical fills, and the recognition rate is 85%. We also calculate the angle and aperture of fractures, the result of which is very good.

The recognition method of small fracture-cave can be applied to big fracture-caves, and the recognition rate is higher than previous methods. Through detailed application results analysis, our method shows a promising capability for grasping fracture-cavity reservoir development regular completely and building an accurate geological reservoir model.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012