Kansas Geological Survey, Open File Report 96-50

Seismic Modeling in the Minneola Complex, Ford and Clark Counties, Kansas: Differentiating Thin-Bedded Morrow Sandstones From Shale in Lower Pennsylvanian Channel Fill

by Joseph M. Kruger, Kansas Geological Survey, Lawrence, KS

Introduction

Lower Pennsylvanian Morrowan sandstones are a major oil and gas exploration target within and along the margins of the Hugoton embayment in Kansas, Oklahoma, and eastern Colorado (Fig. 1). In many areas (e.g. the Stewart Field in Finney County, Kansas), Morrow reservoir units are fluvial-estuarine sandstones which lie within channels incised into the underlying Mississippian limestones (Montgomery, 1996). However, in the Minneola complex in Ford and Clark Counties, Kansas (Fig. 1), the reservoir units are interpreted as barrier bars or shelf sandstones, which were deposited during stillstands of a transgressive sea (Tillman et al., 1985; Clark, 1987, 1995). These sandstones are thicker and more productive within the paleochannels due to differential compaction of a thicker sequence of underlying early Pennsylvanian shales and siltstones, which were deposited on the weathered and incised Mississippian limestone (Fig. 2).

Figure 1--Index map of study area showing the Hugoton embayment and other major tectonic features. Individual fields and associated production in the Minneola complex are shown in the insert (from Clark, 1987).

map of the Hugoton embayment of southwest Kansas

Although both 2-D and 3-D seismic has been used successfully for identifying the channels in which the Morrow sandstones occur (Clark, 1987, 1995; Montgomery, 1996) it has met with limited success in determining whether the channels contain potentially productive sandstones, or are simply filled with shale , siltstone, or tight sandstones and conglomerates. This is particularly a problem for the Minneola complex because the productive sandstones are relatively thin and occur in northwest-southeast barrier bar trends that are separated laterally by non-productive intervals in the Morrow (Clark, 1987, 1995; Fig. 3). Because of this, drilling a well within a seismically identified channel does not necessarily mean it will encounter potentially productive sandstone, even if the channel is relatively thick.

The goal of this report is to use seismic well log modeling to determine if it is possible for seismic data to differentiate a channel that is completely filled with non-productive material such as shale, from one that contains a potentially productive sandstone. Results from this study suggest that differentiating sand from shale is possible with high-resolution seismic imaging, provided the frequency bandwidth is relatively wide, the noise levels are relatively low, and well control is used to help identify the type of seismic anomaly to look for.

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Kansas Geological Survey, Open-File Report 96-50
Placed online Feb. 1997
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