The ResFrac DFIT study was a one-year collaborative effort sponsored by six operators and one service company. The study integrated ResFrac’s unique DFIT modeling capability with the expertise and experience of operators. We performed a top-to-bottom review of DFIT analysis techniques and developed a new step-by-step interpretation procedure. The results were presented at the 2019 URTeC (McClure et al., 2019), and a follow-up paper will be presented at 2019 ATCE on economic implications (Fowler et al., 2019). The results show that in some cases, permeability estimates from DFITs are severely inaccurate, resulting in significantly suboptimal well and fracturing design.
The ResFrac DFIT study was a one-year collaborative effort sponsored by six operators and one service company. The project was motivated by prior work showing issues with conventional DFIT interpretation techniques (McClure et al., 2016). The project integrated the unique modeling capability of ResFrac (fracture propagation and closure, multiphase flow, and wellbore), comparison with analytical relations, field data, and operator experience. It was incredibly rewarding to work with such an outstanding group of engineers and geoscientists.
We performed a top-to-bottom review of DFIT analysis techniques and developed a new step-by-step interpretation procedure. The entire procedure can be performed in an Excel spreadsheet. A large number of ResFrac DFIT simulation were performed and then analyzed using a variety of techniques. An automated interpretation script was built to facilitate testing and iteration. The accuracy of different interpretation methods was compared with the known model inputs. Based on the results, the interpretation methods were refined and new methods were developed. The methods were applied to a large and diverse set of DFITs submitted by the operators. The entire procedure was evaluated and refined by the group in a series of meetings throughout 2018. The results were presented at the 2019 URTeC (McClure et al., 2019), and a follow-up paper will be presented at 2019 ATCE on economic implications (Fowler et al., 2019).
To briefly summarize the key findings:
We developed new equations for estimating permeability from a DFIT, extending existing techniques to account for the effect of wellbore storage and the effect of changing fluid pressure in the fracture over time.
Discovered that multiphase effects can cause ‘false radial’ flow in gas shale reservoirs that leads to a huge overestimate of permeability.
Performed a well and cluster spacing optimization to show the impact of the ‘false radial’ permeability estimate on economic performance.
Proposed a new term ‘contact pressure’ as a way of resolving miscommunication and confusion around the topic of ‘fracture closure.’
Showed that ‘near-wellbore pressure drop’ due to near/mid-field tortuosity should be the primary interpretation for the widespread phenomenon of very high pressure derivative in the first 10-60 minutes of shut-in.
Proposed interpretations of DFITs without a clear pick for fracture contract.
Showed that typical fracture aperture at the contact point is on the order of 0.5-2 mm, reflecting the roughness of in-situ hydraulic fractures.
Identified problems with certain relations that are sometimes used for DFIT interpretation.
Fowler, Garrett, Mark McClure, and Craig Cipolla. 2019. A Utica Case Study: The Impact of Permeability Estimates on History Matching, Fracture Length, and Well Spacing. Paper SPE-195980-MS presented at the SPE Annual Technology Conference and Exhibition, Calgary, Alberta. Link.
McClure, Mark W., Hojung Jung, Dave D. Cramer, and Mukul M. Sharma. 2016. The fracture compliance method for picking closure pressure from diagnostic fracture injection tests. SPE Journal 21 (4): 1321-1339, doi: 10.2118/179725-PA.
McClure, Mark, Vidya Bammidi, Craig Cipolla, Dave Cramer, Lucas Martin, Alexei A Savitski, Dave Sobernheim, and Kate Voller. 2019. A Collaborative Study on DFIT Interpretation: Integrating Modeling, Field Data, and Analytical Techniques. Paper presented at the Unconventional Resources Technology Conference, Denver, Colorado. Link.