3-D Modeling of the Paleocave Reservoir in Tahe Oilfield, China

Tahe Oilfield, the largest marine carbonate oilfield in China, is located in the north uplift of Tarim Basin. With the discovery and development of Ordovician reservoirs in Tahe Oilfield, the paleocave carbonate reservoir has become a new field of reservoir geology study in China. Nevertheless, few effective workflows have been proposed to build the 3D reservoir models. We describe a modeling approach integrating core, well log and seismic data, to reveal the complex subsurface paleocave reservoirs in Tahe Oilfield. The paleocave reservoirs were identified on single wells by comprehensive analysis of the core, logging and drilling data. The tectonic evolution history was reconstructed, thus the Ordovician paleogeomorphology was rebuilt, and paleocave carbonate was divided into the vadose zone and phreatic zone. It was found that in different paleocave zones, the thickness and development probability revealed by well data have obvious differences. The seismic coherence cube was selected as the secondary variables for the modeling, as it showed an obvious correlation with paleocave reservoirs revealed by well data. The quantity probability relationship between the well and seismic coherence were established, and experimental variograms were analyzed and fitted. Then stochastic modeling was applied in each karst paleocave zone separately, integrating the well data and the seismic data, and the 3D distribution of the paleocave reservoirs were present. As the paleocave porosity and permeability cannot be interpreted formed the logging data, reservoir engineering methods were used to calculate the average porosity and permeability for each flow unit. Our method may be useful in characterizing similar subsurface paleokarst systems in other areas.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California