Accommodation Model for Wolfcamp (Permian) Redbeds at the Updip Margin of North America's Largest Onshore Gas Field

 

Martin K. Dubois, Kansas Geological Survey and Robert H. Goldstein, University of Kansas

Purpose

To determine the accommodation and stabilization mechanisms that led to a lateral transition between Permian marine-carbonate-dominated sequences and continental-siliciclastic-dominated sequences at the margin of a giant gas field.

 

In the Kansas portion of the Hugoton Embayment of the Anadarko Basin, Council Grove Group red silts and very fine-grained sands of probable continental origin are up to four times thicker updip than they are in the middle to outer portion of the gently dipping ramp. Interbedded with the siliciclastics are shoaling-upward marine carbonates, the principal gas reservoirs in the fields, that were deposited during times of high sea level on the low-relief shelf. Carbonate units thin to the northwest where the red siliciclastics are thickest. A few of the carbonate units pinch out where the siliciclastics thicken in a position nearly coincident with the field margin. The redbeds have been suggested to be the lateral seal for the field and understanding the mechanisms for depositing the siliciclastics high on the shelf is critical to understanding reservoir geometry of the largest onshore gas deposit in North America.

Major Points

• Much continental siliciclastic accumulation in the Council Grove results from biostabilization (plant and animal-induced) rather than by accommodation related to sea-level rise
• Continental siliciclastics of eolian origin built relief that reduced accommodation for marine carbonates at the updip field margins
• Continental siliciclastics are not a lateral seal for the Panoma Field even though the field margin is coincident with pinchout of marine carbonates
• There is a predictable succession of continental lithofacies controlled by the interaction of climate, glaciation/de-glaciation, and sea level

Approach Describe and analyze thirteen cores of the Council Grove in the Hugoton-Panoma field area. Tie lithofacies to wireline electric well logs. Utilize the Kansas Geological Survey tops set (formation-member level) from 12,000 wells to map thickness of each sedimentary half cycle (marine carbonate-siliciclastic) in the Council Grove. Develop general depositional model to explain sedimentary patterns. Mechanisms considered for deposition of siliciclastics Siliciclastics are marine and accumulation is related to accommodation by sea level rise. Siliciclastics are fluvial (alluvial). Accommodation is from a rising gradient over a low relief surface. Siliciclastics are eolian and stabilized by rising water table associated with rising sea level. Siliciclastics are eolian and stabilized by a rising water table associated with increased rainfall due to a climate change. Siliciclastics are eolian and accumulation was made possible through biostabilization from plants and animals.

Field History

The 70-year old Hugoton and Panoma Field has yielded 34 TCF gas from the Wolfcampian Chase and Council Grove Groups. In the center of the field the combined gross pay is up to 130 meters thick (430 feet) and production is from thirteen fourth-order marine-continental sedimentary sequences. The two fields, Hugoton (Chase) and the underlying Panoma (Council Grove), have been regulated separately, but the two are more likely a common reservoir.