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Based on the Filling Evaluation of Carbonate Paleokarst Reservoir poroperm characteristics in Tahe Oilfield, Tarim Basin

Kang, Xun; Jin, Qiang; Fei, Tian; Li, Yang; Zhang, Hongfang

Paleokarst fracture-cave in Ordovician carbonate is the main productive reservoir in Tahe Oilfield. Due to multi-stages of karstification and various cave fillings association, the paleokarst reservoir is complexly anisotropic. So it is necessary to evaluate fracture and caves' physical property accurately for the assessment of reservoir and its actual production capacity.

Based on the analysis of paleokarst reservoir characteristics through comprehensive study of core observation, imaging logging, core testing results, well testing and early producing capacity, etc, it is considered that paleokarst reservoir physical property are mainly controlled by the degree of fracture-cave development and cavity filling. Taken the main control factors into consideration, firstly fracture-cave and cavity filling recognizing equations was built by using conventional logging data which is demarcated by core and FMI; secondly cave development section was divided into no filling section and 3 kinds of fillings including mechanical sediment, collapse breccia and chemical deposition filling; then porosity and permeability logging interpretation model was built based on the filling type and fracture occurrence; finally the interpretation model was tested and verified on the basis of core analysis and production data.

This interpretation model is proved scientific, rational, and practical when applied to 146 wells in No.4, 6 and 7 area of Tahe oilfield. This paper reaches some conclusions: Collapsed breccia and coarse mechanical sediment have good porosity and permeability, which is in keeping with well's relatively high production; The small caves of less than 0.5m height have better physical property when compared to fractures although fractures improves reservoir's physical property obviously. This model provides a solid foundation for further geological modeling and the efficient exploitation of carbonate karst reservoir.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013