Guizhou modern karsts as analogues for paleokarst reservoirs in the Shunbei oil field, Tarim Basin, China

Abstract

The modern karst systems of Guizhou Province in southern China are examined as the key analogues for fault-controlled paleokarst reservoirs of the Shunbei oil field in the Tarim Basin in northwestern China. The size, distribution, and geometry of karst features are quantitatively described on millimeter-to-kilometer scales, and then we discuss their relationships to the faults, fractures, and bedding surfaces. A three-stage evolutionary model of the modern Guizhou karst is proposed, illustrating how faults and fractures control the flow pathways of drainage and the extent and processes of karstification. Middle Ordovician karstification in Shunbei was controlled by strike-slip faults and followed a similar pattern with Guizhou modern karst. Surface drainage flowed mostly along the gently sloping stratigraphic boundary between the Middle Ordovician and the Upper Ordovician (T74) stratigraphic surface and then downward along steep strike-slip faults. The consistency between the No. 1 fault strike and the southwest-oriented slope resulted in the formation of large-scale underground interconnected paleokarst cave systems at depths of 60 to 107 m. However, No. 5 and No. 7 faults formed fault-controlled paleokarst cavity along deep faults at depths of 0 to 450 m, displaying heterogeneous vertical distribution and poor connectivity in plane. These findings can aid in the design of well trajectories and thus improve exploration and development efficiency in Shunbei and similar fault-controlled paleokarst-dominated carbonate reservoirs.