Hunton Limestone: A Highly Fractured, Natural Gas-Driven, Multiple Pay Carbonate Reservoir Within the STACK Play, Central Oklahoma
Abstract
The Hunton Limestone formation lies within the STACK play in central Oklahoma, as well as
beyond the defined boundary in north-central and northwest Oklahoma. Structurally, the productive
formation lies along the border of the Anadarko basin to the southwest and the Anadarko shelf to the
northeast. The Hunton Limestone does not contain primarily conventional porosity as viewed through
electric logs from thousands of historic vertical wells. However, this carbonate reservoir, sourced from
the overlying Devonian Woodford shale, internally provides multiple characteristics of secondary
porosity, such as: diagenesis, karsting, vugular porosity, dolomite, and regional fracturing. From 70+
horizontal wells drilled in central Oklahoma, image log analysis has determined that the entire Hunton
interval contains a large network of partial and open fractures that span across the region. These
fractures are the primary feature that provides the pooling of hydrocarbons within the reservoir. The
Hunton formation is both truncated structurally by the Anadarko shelf and stratigraphically by pinching
out to the northeast by the underlying Sylvan Shale. The Hunton formation can be sub-divided into
three different producing formation: Upper Hunton (Frisco and Bois d’arc limestones), Middle Hunton,
and Lower Hunton (Chimney Hill formation composed of the Clarita and Cochrane limestones).
As a carbonate formation with unconventional porosity, the completion process must also be
viewed unconventionally. The fracture network within the formation must be exploited to obtain a long
term producing and naturally flowing horizontal well. With a higher than average recovery efficiencies
for STACK horizontal wells, EUR’s for the Hunton Limestone intervals range from 125k BO to 385k BO
and 2.5 BCFG to 3.5 BCFG. The secondary porosity inherent within the formation, the regional fracture
network, and custom fracturing design, ultimately provides evidence for a large and economically viable
hydrocarbon reservoir within the STACK play of central Oklahoma.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019