GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 34-16
Presentation Time: 9:00 AM-5:30 PM


AHLERT, Alexis K., SIMON, Rebekah, BROWN, Megan R.M. and GE, Shemin, Department of Geological Sciences, University of Colorado Boulder, Boulder, CO 80309

For oil and gas wells in Colorado, a circular spacing regulation exists that requires wells to be spaced 235.5 ft (71.8 m) in diameter apart, yet recent changes in hydraulic fracturing treatment in the Piceance Basin has caused some oil and gas wells to experience hydraulic communication (HC), defined here as a transfer of pore pressure across a porous medium. During HC, formation water enters the producing borehole at the front of the pressure wave, and must be removed before the well is brought back into production. At this time, several post-recovery wells have come back on line, but months later, have not recovered their original production rates. It is hypothesized that during HC, the drainage divide between impacted wells is permanently shifted. To test this theory, we utilize MODFLOW to model a generalized two-well system in which a producing well and hydraulic fracturing well are ~one mile (1,610 m) apart. This model tests how geologic heterogeneity in aquifer transmissivity and storativity, and engineering parameters including well spacing and hydraulic fracturing treatment volume affect the total well system. Through sensitivity analyses, we can determine which parameters have the greatest effect on HC. The analytical Theis solution defines preliminary bounds of hydraulic head for the well system. For a homogeneous, isotropic medium, the analytical solution suggests that the maximum hydraulic head value over the duration of injection (24 hours) is approximately 300 meters. Overall, it is expected that systems with lower permeability, increased well spacing, and minimized treatment fluid volumes will decrease the probability of well-to-well HC in the Piceance Basin.

Hydraulic communication in the Piceance Basin must be at least partially due to the geologic heterogeneity of the area. Many well pairs are located less than one mile apart, and have not experienced HC during treatment. However, for impacted wells, HC can cause both unexpected short-term expenses and permanent economic loss. It is therefore critical to understand the appropriate geological parameters for communication minimization, despite a fairly limited number of occurrences thus far. Additionally, a better understanding of HC between wells will provide new knowledge for Colorado regulators to reevaluate their current spacing regulations.