The internal karst reservoirs in the slope area of Tahe oilfield

Tarim Basin have attracted more and more attention as further exploration and development were carried out in the weathering crust karst reservoirs in the buried hills of the main blocks in the field.It is generally agreed that faults control the formation and distribution of karst reservoirs.Based on reservoir classification

the paper analyzed control effect of faults upon karst reservoirs and their distribution and discussed forming mechanism and evolving characteristics of the reservoirs through study of core

thin sections

logging and drilling as well as seismic data.A coupling relationship between extent and phases of development of faults and karst reservoirs was revealed during the analyses.Multi-phased and inherited faults of grade Ⅱ and Ⅲ-1 seemed to have a more prominent controlling effect upon the karst reservoirs.Horizontally

the reservoirs distributed as belts along faults; and vertically

they were observed to occur within intervals 0-50 m or 100-150 m below the top of the Ordovician Yijianfang Formation.The paper also suggested that these reservoirs were formed mainly by meteoric water dissolution

TSR (Thermochemical Sulfate Reduction)

hydrothermal dissolution

and hybrid dissolution.The Early Hercynian was believed to be the main stage for the development of the fault-controlled karst reservoirs in the field.