Geological characteristics of ‘strata-bound’ and ‘fault-controlled’ reservoirs in the northern Tarim Basin: taking the Ordovician reservoirs in the Tahe Oil Field as an example

The marine facies carbonate reservoirs in the northern Tarim Basin were studied using high-resolution 3D seismic data, as well as a large amount of actual drilling data and dynamic production data. The carbonate fractured-and-vuggy reservoirs in the study area were distinguished into two types:strata-bound karst reservoir and fault-controlled karstic-fault reservoir. The former was developed in the buried hill of the paleokarst system in the northern Tarim Basin, which can be further divided into two subtypes:residual hill type and paleo-channel type. Reservoirs are characterized by "vertically superimposed and quasi-stratified distribution" on the macroscopic scale, and feature large changes in reservoir space, coexistence of caves, pores and fractures, relatively contiguous reservoir units, and complex oil-water relationships. The karstic-fault reservoir mainly developed in the covered area of Middle-Upper Ordovician, which is controlled by different ordered strike slip faults and related dissolutions. The karstic-fault reservoir is a special type of oil and gas reservoir existing in nature. It has unique hydrocarbon accumulation characteristics, such as different sections of accumulation along fault belt, across different strata vertically and discontinued distribution and so on. The karstic-fault reservoir is a new trap type and a new target in deep carbonate oil and gas exploration and development.