Structural model and developmental characteristics of typical carbonate crack-cave systems under warm and humid climate conditions

Carbonate rocks can form typical crack-cave systems under warm and humid climate conditions. The Ordovician carbonate rocks has three tectonic uplifts in the Tarim basin, resulting in depositional break between Ordovician and Silurian, Carboniferous strata. The ancient Tarim land was located in low latitudes during the Devonian and Silurian, and had a tropical or sub-tropical climate which was favorable to generate large karst crack-cave systems. The Tarim area in Devonian and Silurian had the similar climate characteristics to the modern South China, and experienced intense karstification. Based on outcrops investigation and analysis of cores, seismic and logging data, combined with the modern karst theory, this work makes a comparative study and summarizes spatial structural characteristics of carbonate fracture-cave systems. Such typical systems under warm and humid climate conditions are divided into 4 types: underground rivers, karst caves, karst pores, karst seams. Furthermore, the underground river is subdivided into 3 sub categories of single pipe, multi pipe and corridor pipeline, and the cave is subdivided into the hall type, cave type and vertical type. Then eight corresponding structural models are established, and their characteristics are summarized. This will help to reveal the pattern of development and distribution of crack-cave systems in Tahe oil field, and provide a reliable basis for oil geological modeling.