Characteristics and favorable controlling factors of karst reservoirs within the uppermost part of Ordovician in Dongpu Area, Henan Province, China

Abstract: Karst reservoir within the uppermost part of Ordovician, Fengfeng Formation and Majiagou Formation, in Dongpu area experienced a variety of karstifications. Based on outcrop, core data and thin sections, wireline... [ view full abstract ]

Abstract: Karst reservoir within the uppermost part of Ordovician, Fengfeng Formation and Majiagou Formation, in Dongpu area experienced a variety of karstifications. Based on outcrop, core data and thin sections, wireline log, associated with regional geology data, characteristics of karst reservoir within the interest interval of the study area were identified, types of karst reservoirs were distinguished and consequently favorable controlling factors of various karstification were analyzed. Our results revealed that the karst reservoirs were dominated by grain limestone, dolomitic limestone, mud-sized crystalline limestone, silt-sized to fine sand-sized crystalline dolostone, gypsum-bear dolostone and algae dolostone, and the main reservoir spaces were cracks and pores, dolostone reservoir had a higher porosity and permeability than limestone. Favorable controlling factors of various types of karst reservoirs were different. Penecontemporaneous karst reservoir was mainly controlled by sedimentary facies, weathering karst reservoir was mainly controlled by palaeogeomorphology, buried karst reservoir was mainly controlled by fault, fracture development. Weathering karstification played a crucial role in the development of karst reservoir within the uppermost part of Ordovician in Dongpu area, buried karstification reformed the previous reservoir and penecontemporaneous karstification made little contribution to the reservoir. Paleokarst groove development zone in Machang area, superimposed area of karst steep-slope zone and burial stage large fracture development zone could be regarded as the most favorable zone.