STACK-SCOOP Basin Study on Hydraulic Stimulation
By Ralph E. Davis Associates, an Opportune LLP company
The Woodford Shale is a deep marine shale of Devonian age (420-358 million years ago), that produces both gas and oil depending on the location of wells in the Anadarko basin. It is a source rock with organic derived porosity and production is primarily driven by matrix porosity and over-pressure.
To recover commercial quantities of hydrocarbons from the Woodford shale play the wells need to be hydraulically stimulated by pumping fluids and proppants into a well. These fluids are pumped into the well faster than they can escape into the formation, causing pressure to rise and keeping the fractures from closing.
The design of the hydraulic stimulation depends on rock characteristics and the fluids in the formation. Designs are based on some of the following parameters and optimized to minimize formation damage and increase production:
- Hydrocarbon type
- Viscosity requirements
- Fluid rheology
- Economics of fluid
- Experience with formation
- Laboratory data
- Material availability
- Proppant selection
There are primarily three types of fracturing fluids currently used. These are slick water, linear gel and crosslinked gel. All three of these frac fluids have different properties and applications.
Figure 1: The area of interest in the Anadarko Basin for Woodford Shale.
RED forecasted EUR (Estimated Ultimate Recovery) on several Woodford shale wells and identified the hydraulic stimulation type associated with these wells.
Figure 2: Histogram of Woodford oil & condensate well EUR with stimulation type identified.
Figure 3: Histogram of Woodford gas well EUR with stimulation type identified.
Figure 4: Histogram of Woodford wells by stimulation type.
In conclusion, the type of well fluids produced has a significant role in choosing the optimal treatment type. The Woodford gas wells respond better to slickwater stimulation while the oil & condensate wells appear to show better performance with a gelled stimulation with the data sampling used here. Even with that conclusion, Slickwater Frac appears to method of choice for stimulating Woodford Shale wells in the assessment area (Figure 4). There may be cost and operational reasons for this preference, Gelled jobs require more QC and are more complex chemically than Slickwater jobs. Chemicals in gelled jobs need to be blended to correct ratios, water quality needs to managed and other operational aspects related to increased treating friction needs to be accounted for.
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