HYDROGEOMORPHOLOGIC ARCHITECTURE AND ITS CONTROL ON PALEOCAVES IN EARLY HERCYNIAN, TAHE OIL FILED, TARIM BASIN

The Ordovician paleocave reservoirs in Tahe area had been discovered to be a giant oil field. According to the tectonic evolution history, Ordovician had undergone a long time of continuous uplift and exposure in Hercynian, and suffered telogenetic dissolution. As a result, a large amount of caves were produced to be different scales of cave systems.

Three dimensional seismic data, logging, and cores were utilized to understand the characteristics of paleocaves, integrating modern karst theories and seismic attributes extracting and related imaging techniques. It showed that the morphology and features of paleocaves in east and west of Tahe area varied a lot. Branchwork, network maze and single passage caves shaped to be a complete system in east, while isolated caves acted as the primary categories in west. In addition, paleocaves in east tended to be larger, deeper and more connected as well.

In order to illustrate the mechanism of paleocaves, we reconstructed karst paleo-geomorphology and paleo-drainage system of Ordovician in Tahe area. The following results were demonstrated. (1) East area developed in karst plateau and karst slope, and peak cluster and karst hill acted as the main landform units with high relief. Besides, some typical landscape combinations consist of dry valley, swallet steam, canyon and natural bridge were formed. Moreover, an integrated drainage system made up of surface and underground hydrologic networks had come into being. (2) While west area developed in karst depression holding gentle topography gradient and karst hills with relatively lower relief were found. The surface water network was marked by sinuous features in association with lateral erosion, and the underground water tended to be inconspicuous.

We concluded the hydrogeomorphologic architecture to be “surface and underground drainage system pattern” in east, and “surface drainage pattern” in west. Actually, thus two types of hydrogeomorphologic architenture reflected unique hydrogeological and hydrokinetic conditions, which led to the formation three relevant categories of paleocave development models including single passage, branchwork passage and isolated caves model.