Characterization and three-dimensional genetic mapping of the multi-layer Ordovician paleokarst reservoirs, Tarim Basin

Abstract

This paper describes a detailed approach for the integration of the core samples, imaging and conventional well-logging data and high-quality seismic data to delineate the complex paleokarst system in the Tahe Oilfield. First, caves’ recognize equation is developed using conventional welllogging data, which is demarcated from core and image logs with a cave resolution of approximately 0.5 m. Second, time-depth conversions for 97 wells are identified, and the recognition results in the signal wells are tied to seismic dataset. Third, after determining the cutoff values of the host rocks and the caves in acoustic impedance, the acoustic impedance inversion volume is identified to recognize the spatial construction of the paleokarst reservoirs. Forth, the 3D mapping and visualization of the paleokarst reservoirs are achieved by tracing the distribution of caves based on the acoustic impedance inversion volume. This method is applied in the area of Well T615, and the constructions of two paleokarst layers in the run-off zone are interpreted. Additionally, according to the hydrology genetic relationships, the caves are divided into sinkholes, main channels and branch channels. The areas where the main channel and intensive branch channels developed are conducive to hydrocarbon reservoirs. Our method for paleokarst reservoirs characterization and genetic analysis is applicable to Tahe and other similar paleokarst oilfields and can effectively guide the exploration and exploitation of paleokarst reservoirs.