Despite having drilled thousands of horizontal wells into the Niobrara and Codell formations in the DJ Basin, the industry still hasn't settled on a preferred set of parameters for well spacing or frac design. Great Western Petroleum designed this project in 2019 to better characterize both natural and induced fractures in the formation, using an array of diagnostic tools across multiple disciplines.
We combined logging in both pre-completion unstimulated horizontal wells and post-completion fracture observation wells to characterize the natural fracture set and the induced hydraulic fracture set. After completion, we integrated geochemical analyses, pulse tests, and production surveillance techniques to study the dynamic connectivity between wells both within individual benches and between benches. Finally, we used a history-matched reservoir simulator to integrate as many data sets as possible into a single interpretation.
The hydraulic fracture network that was observed from the fracture observation wells was vast and dense. We observed over 1,400 hydraulic fractures and over 3,000 natural fractures on interpreted image logs that were run on the two wells. Notably these fracture sets were near perpendicular to each other suggesting a change in maximum principal stress between natural fracture formation and hydraulic fracture. As expected, we saw strong communication between wells based on all the data sets based on the spacing and frac design used. The different diagnostic data sets led us to similar conclusions, despite a wide range of data acquisition costs. We observed a high degree of vertical communication between the wells, but the communication between wells in the same bench was minimal. This trend continued over time with all the datasets as well. The strong interwell communication led us to adjust our well count, while taking frac volumes into account. We also calibrated the low-cost data sets for future work, which we began applying to new pilot projects in 2020. However, there were key difference between the different data sets that lead to important conclusions about the time-dependent behavior of inter-well communication.
This is the first time for these kinds of data sets to be integrated into a single publication, and the first time for several of these data sets to be published from the DJ Basin. Our work points to the possibility of inferring key reservoir characteristics from low-cost data sets like geochemistry, pulse tests, and basic production surveillance techniques with infrequent collection of high-cost datasets like post-frac logging. These low-cost datasets also have the advantage of minimal impact on operations. Our shut-in time for pulse tests has been decreased to a few hours, while still providing quantifiable interwell communication. Additionally, we used the interpretations for this project to design future spacing pilots that we believe will substantially improve well economics.
This project was only possible through the collaboration across petrotechnical disciplines, from drilling engineering and geophysics as we drilled the FOW's, to petrophysics and geochemistry as we characterized the rock and fluid properties, to reservoir and production engineering as we analyzed pulse tests and monitored production performance. As the title suggests, this project could only have been achieved by a multi-disciplinary team.
