Predicting Seismically-Thin Sandstone Reservoirs by Integrating Tectno-Paleogeomorphology and Seismic Sedimentology: A Case Study

Xu, Ligui; Zeng, Hongliu; Xiugang, Pu; Wang, Guizhong; Liu, Wanhui

While the ultimate solution for ultra-thin (1-10m) sandstone reservoir prediction is to promote high-resolution seismic acquisition and processing, in many cases we can apply improved interpretation procedures to achieve similar goal with low budget. The major challenges include weak seismic signals from thin beds, strong interference from host rock, and a requirement for high S/N data and adequate impedance contrast between reservoir and non-reservoir facies. A workflow that integrates techno-paleogeomorphologic analysis and seismic sedimentologic mapping has proved to be effective in helping meet the challenges in studying the ultra-thin (3-8m) lacustrine sandstones of Paleocene in Kuqa Depression, Tarim Basin, China.

The reservoir sequence was deposited in a shallow lake directly on the Cretaceous regional unconformity. A normalized seismic time-structure map revealed techno-paleogeomorphology of top Cretaceous unconformity, which uncovers a subtle incised-valley system that seemingly controlled sediment source, sink, and dispersal pattern of the Paleocene fan-delta systems. Sandstone lithofacies were imaged by seismic sedimentology with stratal slices made from 90-degree phased and well-calibrated seismic data. Sandstone-prone facies are characterized by fan-shaped and tunnel-shaped amplitude anomalies that reside in and in front of the incised valleys on the unconformity surface. Although sandstone pinch-out line is difficult to determine because of the lack of adequate well control, predicted thin-sandstone reservoir patterns fit well with sandstone thickness and pay data in available wells, which provides confidence for future exploration and can be used to predict new drilling locations in the area.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013