Imaging the Morrow A Sandstone Using Shear Wave VSP Data, Postle Field, Oklahoma

Morrow sandstones constitute important oil-producing reservoirs in the Anadarko Basin in the Mid-Continent Region of the USA. Characterization of the Morrow A sandstone reservoir in Postle Field, Texas County, Oklahoma, is challenging due to its small thickness, low acoustic impedance contrast with the surrounding Morrow shale, and lithological heterogeneity. Shear wave data have been documented as a promising solution for imaging the Morrow A sandstone. Vertical seismic profiling (VSP) offers the potential to enhance shear wave imaging of the thin heterogeneous Morrow A sandstone at Postle Field. The zero-offset VSP results confirm the advantages of shear wave over compressional wave in imaging the Morrow A sandstone. Also, the final shear wave VSP image shows that, applying the proposed processing flow, we are able to image the Morrow A sandstone where the thickness is as thin as 8.5？m. 1. Introduction Pennsylvanian upper Morrow sandstones (Figure 1) constitute major oil-producing reservoirs across southeastern Colorado, southwestern Kansas, western Oklahoma, and northern Texas. They consist of multiple-stacked lenticular sandstone bodies formed within valley-fill complexes. The Morrow A is an oil-producing sandstone mainly in Oklahoma [1–3]. In this study, we mainly focus on the Morrow A sandstone in Postle Field, Texas County, Oklahoma (Figure 2). Figure 1: General stratigraphic column (left) and detailed stratigraphy column (right) show the main formations at Postle Field, Oklahoma. The Morrow A sandstone is the main oil-producing reservoir in this field. Shale layers between the Morrow sandstones are called the Morrow shales which are of important significance for characterizing heterogeneity in the reservoir. Figure 2: Postle Field is located in Texas County, Oklahoma. The RCP study area, 4.02？km 4.02？km, is in the Hovey Morrow Unit (HMU). The Morrow A sandstone thickness, according to the well data, varies between 0？m and 21？m, and it is thinner at the northern part of the study area. The VSP well (HMU 13-2) is located where the Morrow A is thin. The VSP data, with higher resolution than the surface seismic data, provides the opportunity of delineating the Morrow A sandstone extension. Compressional wave studies have been mostly used in the past for characterizing the Morrow sandstones [4–7]. Briefly, there are two main challenges with characterizing the Morrow A sandstone based on compressional data: first, the thickness of the Morrow A sandstone is below the tuning thickness [6, 8] and secondly, the acoustic impedance contrast between the