Visualizing the Relationship Between Complex Geologic Features and Varying Gas Oil Ratios of the Mississippi Limestone/Woodford Shale System Across the Midcontinent Region

Ralph Williams and Danielle Leighton

The Mississippian play represents a challenge due to its large areal extent, dramatic depositional and structural features and substantial variance in gas oil ratios. The study area of Texas, Oklahoma and Kansas north of the Ouachita Uplift has multiple arches, uplifts, anticlines, basins and sub-basins including Anadarko, Arkoma, Cherokee, Dalhart, Sedgwick, Forest City and Salina. Visualizing the play area represents a huge logistical challenge surmountable using a completely digital approach. Over 60,000 digital well logs with production information (of the 600,000 total wells in the study area) were interpreted to create a detailed, age-dated stratigraphic framework and production overlay. Using this framework, it was determined that over 20,000 of the digital wells penetrate the Mississippian and the following features were observed: -The Mississippi/Woodford system is sandwiched between 2 major unconformities indicating that: 1-Much or all of the Mississippian has been removed, placing it in a subcrop position below the Pennsylvanian strata in many areas; 2-The Mississippian was deposited directly upon limestone strata of the Ordovician resulting in a challenge identifying the base of the Mississippi Lime -Large scale progrades or depositional wedges -Major facies changes from limestone to shale to organic shale to clastics -Pre-deposition uplifts resulting in onlaps -Post-deposition uplifts resulting in total or partial erosion of the Mississippian The production data overlay reveals other notable phenomena: -Many Mississippian completions with varying formation names are comingled with strata above and below -Gas oil ratios and the classification of whether a well is gas or oil vary wildly Digitally imaging the complex Mississippian and Woodford plays across the midcontinent region allows visualization of the relationships between the many complex geologic features and varying gas oil ratios and builds a solid foundation for sweet spot identification. 

AAPG Search and Discovery Article #90176©AAPG Mid-Continent Meeting, Wichita, Kansas, October 12-15, 2013