Gas Production Variability from Wells Drilled in the Marcellus Shale, Tioga County, PA: A Case Study
Substantial production variability has been observed across a 5800 acre development area in central Tioga County, Pennsylvania. The drilling of forty-seven wells began in July of 2009 and was completed in August of 2011. The wells, drilled from eleven pads, were completed and have been flowing to line for at least six months. Average well spacing is approximately 920 feet. All wells are producing dry gas.
Subsurface variability is primarily related to structural complexity; however variations in reservoir quality could also play a role in the production differences but is poorly understood due to limited data sampling. Moreover, spatial and stratigraphic distribution of geomechanical properties are not well constrained and may significantly influence the overall success in this and other areas. Seismic discontinuities extracted from 3D volume processing may provide some clues regarding distribution of variability in well performance.
Differences between completion methodology and flow back conditions among wells may also contribute to production variability. Evaluating the details of completions methods is beyond the scope of this discussion, but is recognized as an important variable to control for when trying to correlate reservoir properties and production history.
Key post-development takeaways of this area include: increase vertical well control and acquire 3D seismic as early as the business model can justify. Sophisticated log suites from additional vertical wells would have better helped constrain changes in reservoir quality, stress and fracture distribution. Most importantly, the early integration of these data sets can help optimize capital outlay during drilling and completion operations.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012