In the New Mexico Delaware Basin, previous completion strategies for 2nd Bone Spring horizontal wells have left pay behind pipe by only perforating and stimulating up to the 80° inclination point at the heel. In the new heel frac program, candidates were first screened based on the amount of remaining pay from top perforations. Detailed geologic and engineering analyses were carried out to investigate reservoir quality and estimate potential incremental production rates. To refine the candidate list further, wells were evaluated for casing integrity, cement integrity, lift type, lift capacity, battery capacity, and gas sales capacity prior to being entered into the program. Heel frac completions to monetize the heel pay have been implemented on multiple wells. Production results varied from well to well, but overall, the average incremental production performance was higher than anticipated, and the program has proved to be economic. A number of operational issues were encountered during the program, and the causes and remediation methods have been investigated.
In the most recent heel frac programs, refracs of the last existing stages were added due to the low incremental cost of adding a refrac stage. Proppant tracers and chemical tracers were used to understand the stimulation and diversion effectiveness and evaluate the incremental production gained from the new heel and refrac stages. In this study, comprehensive post-job hydraulic fracture diagnostics were done by integrating proppant and chemical tracer results, conducting stimulation treatment analysis, producing a geologic evaluation, and monitoring the production performance. Early chemical tracer results showed that re-fracturing the last existing stage added measureable production, and it was deemed economic due to the minimal added cost. Proppant tracer results demonstrated that diversion with ball sealers was not effective in the refracturing stages. Unstimulated clusters and proppant concentration detected at non-targeted perforations were observed in some stages. Additionally, both proppant tracers and fracture treatment behavior suggested communication behind pipe between stages where it is suspected that bad cement and changes in rock properties along the wellbore may have contributed to the stimulation ineffectiveness.
These case studies have shown that the integrated fracture diagnostics provide a good understanding of stimulation effectiveness, the causes of ineffective stimulation, and the impact on production economics. Lessons learned from this study will be applied to optimize future heel frac/refrac designs and assist with candidate selection and data gathering.