Understanding the Stimulated Rock Volume (SRV), the Drained Rock Volume (DRV) and communication between parent and child wells is critical to creating a development plan for an unconventional reservoir play. This study shows application of a set of cost-effective techniques using oil and water geochemistry, along with an extensive sampling program to describe the interplay of the reservoir, the well completion, and well spacing/stacking layout in the Bakken/Three Forks Hybrid Play.
ConocoPhillips has developed a novel time-lapse geochemistry technology calibrated to core-extracted oils to cost effectively ascertain vertical drainage, which is among the most critical parameters used in determining optimal field development strategies. Water geochemistry is another technology that can be used in conjunction with time-lapse oil geochemistry to evaluate the stimulated rock volume and child-parent interactions. More than 1000 oil and 3000 produced water samples from approximately 100 Bakken and Three Forks wells have been collected across ConocoPhillips’ Bakken acreage. The analytical program consists of a suite of GC, GCMS and SARA fractions for oils, and total ion chemistry (cations and anions) and stable isotope geochemistry for the produced water samples.
Our results show, in the Williston Basin, thin reservoirs coupled with large stimulation jobs result in large vertical hydraulic fractures and extensive out-of-zone drainage. We clearly demonstrate that produced waters are mixtures of stimulation and formation water. The stimulation water to formation water swap occurs very rapidly, with only a small portion of stimulation water being recovered at the wellhead. Integrating oil and water geochemistry allows us to better assess the extent of the SRV (water) and the dynamics of DRV (oil) in a cost-effective way. The relationship between SRV and DRV can be used to evaluate differences between completion designs, infer communication between wells, and ultimately optimize the development plan.
We clearly demonstrate that water geochemistry can provide comprehensive insight into the dynamics of flowback and the fate of the stimulation water. It sparks research interest in the water-rock interaction and the impact of water on production in unconventional reservoirs. With more and more infill and refrac wells, water geochemistry can also be a very useful monitoring tool to access the extent of the stimulated rock volume. A combination of oil and water geochemistry can help to gain a deeper understanding of SRV/DRV dimensions and their relations to completion design.