Characteristics of Abnormally-pressured Gas Compartments, and Potential Sealing Mechanisms in the Spiro Sandstone: Arkoma Basin, Oklahoma

Abstract

This investigation provides some plausible explanations for generation of abnormal pressures in Spiro sandstone reservoirs of the Arkoma Basin. These reservoirs are thrust and completely sealed compartments. A better understanding of the geometry and sizes of these compartments may lead to a more accurate estimate of the basin's natural-gas reserves. In addition, the findings may also lead to significant decreases in the risk involved in exploring for natural gas in such a tectonic setting. Compartmentation processes and sealing mechanisms were studied by integrating various geological and geophysical models and information. These include, structural and tectonic framework of the basin, depositional setting, diagenetic patterns, and pressure regimes. The significant source of information was produced by modeling of the Wilburton area in the Ouachita fold and thrust belt. Chamosite-bearing facies were identified as being the best reservoir quality in the Spiro sandstone. The spatial relationships ofthe models and information was used to model basin diagenesis. Diagenetic patterns observed were greatly influenced by mechanical as well as chemical processes involved in the basin evolution. For example, diagenetic cements from various pore fluids, and shale smears from fault actions. These patterns were useful in evaluating various hypotheses related to the development of seals and the preservation and/or destruction of primary porosity.