Differential structure of Ordovician karst zone and hydrocarbon enrichment in paleogeomorphic units in Tahe area, Tarim Basin, NW China

ZHANG San,JIN Qiang,HU Mingyi,HAN Qichao,SUN Jianfang,CHENG Fuqi,ZHANG Xudong

Table 1 Identification marks of fracture-caves in different karst zones of Ordovician in Tahe area.

Karst zone Flow channel Flow pattern Fracture-cave structure Drilling borehole Log Seismic Type Filling GR RLLD/RLLS Epikarst Fault Fracture Fissure Surface runoff Diffuse infiltration Surface river Doline Disorderly karst debris Not expand Toothing high value (30-50 API) Mid-low value No difference Beaded reflection, V shape Karst vug Karst crack Calcium Weak filling Expanding leakage- overflow Toothing low value (7-9 API) Mid-high value Positive difference Cluttered reflection, Quasi-continuous Vadose Fault Fracture Vertical flow Water-storage cave Karst well Collapse breccia Weak filling Expanding, serious leakage Toothing low value (10-20 API) Mid-low value Positive difference Beaded reflection, isolated vertical distribution Runoff Fault Unconformity Underground river Hrizontal flow Hall-like cave Mainstream cave Tributary cave Collapse breccia and sedimentary rocks High filling Expanding, leakage Cluster high value (50-100 API) Very low value Positive difference Beaded reflection, horizontal banding distribution Phreatic Bedding Pore Laminar flow Karst pore and crack Gray-green clay High filling Not expand Finger high value (20-50 API) High value No difference Bed-parallel reflection