Project Information
Geological characteristics significantly affect energy extraction and well integrity. Therefore, prior knowledge about the geological and hydrogeological setting of the site is vital for determining the feasibility of any geothermal project.Oklahoma is characterized by great thicknesses of sediments preserved in a series of major depositional structural basins separated by orogenic uplifts created mainly during Pennsylvanian time (Cranganu et al., 1998). From these provinces, our location lies on the stable Cherokee platform. Hydrogeological analysis shows that Oklahoma's aquifers can be divided into two general groups: bedrock and alluvium or terrace deposits. The bedrock aquifers (e.g., Permian and Pennsylvanian rocks- represented in purple and green in the below figure) are composed of sandstone, interbedded sandstone-limestone-shale, and soluble carbonate and evaporite (limestone, dolomite, and gypsum). The alluvium and terrace deposits aquifers (Quaternary- shown in yellow in the below figure) consist of unconsolidated sediments found along rivers and streams. Oil and gas wells located in the area are primarily perforated in the Skinner Formation. This Pennsylvanian unit is the subsurface equivalent of the Chelsea sandstone from the Senora formation and consists of fluvial and deltaic facies (OSGS, 1996) that reach >100 ft of thickness when stacked. Reservoir properties average 15% for porosity and 15 mD in permeability. Other properties and oil production of the formation are well defined in OSGS,1996.
Map of geologic provinces of Oklahoma (Cranganu et al., 1998) overlapping the map of major sources of groundwater in Oklahoma after The Oklahoma Geological Survey (1984). The study area is indicated with a red star.
Another geologic aspect pertinent to our study is seismicity induced due to the injection and production operations. Shawnee area has experienced a historical increase in seismicity since 1973. The below figure shows the historical record of earthquakes (colors) and their associated magnitude (circle size). However, no high seismicity is interpreted out of the map for the studied area, having a 5-10% of damage chance. Few events on the ~4-magnitude order occurred in the 2010-2011 period, while minor earthquakes are associated with recent periods.
Seismicity in Oklahoma. Colors indicate the period of occurrence, and circle size indicates magnitude. USGS (2017).
To assess the geothermal resources within the targeted area, our team performed a reservoir simulation study using the abandoned oil wells near the targeted site. A 3D reservoir model was created on Petrel software using the subsurface data obtained from available well logs and reports. Then, the reservoir model was exported to STARS software from Computer Modeling Group (CMG) to assess the potential geothermal energy for the system's expected lifespan. The below figure shows the simulation model built for the project, including the injection and production wells. The estimated energy demand of the targeted buildings with a combined spatial area of around 730,449 ft2 is 54.91 MMBTU/day.
Schematic of the reservoir simulation model.