Key seismic exploration techniques for foreland thrust belt: A case from the complex deep subsalt structure of Kuqa, Tarim Basin, Western China

Abstract

The Kuqa area of the Tarim Basin is a typical foreland thrust belt. Abundant petroleum resources are stored in the complex subsalt structures at depths greater than 6500 m. The extremely rugged surface, the severely deformed gypsum-salt cap above the reservoir, and the large burial depth of the overthrust target make it difficult to accurately delineate the target structures. Those geologic challenges translate into geophysical difficulties of complex seismic wavefields, low signal-to-noise ratio (S/N), and poor imaging accuracy, which compound the exploration challenge in the Kuqa area. To meet the exploration challenge, a research campaign has been conducted since 2005 to integrate seismic acquisition, processing, and interpretation. After almost a decade of research effort and pilot applications, a set of techniques, comprised of wide-line large-array acquisition, anisotropic prestack depth migration under rugged topography, complex structure modeling, and structure mapping with varying velocities, was developed. The use of these techniques has much improved the S/N, imaging accuracy, subsequent interpretation, and well placement. As a result, the success ratio of exploration drilling has increased from less than 25% to more than 64% in the Kuqa area of the Tarim Basin.