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Traditionally, plug selection, compared to variables like proppant intensity, fluid intensity, and cluster spacing, is often overlooked in completions design. However, more and more experiments with advanced downhole diagnostics expose the criticality of plug choice and demonstrate the hidden dangers of poor isolation. This paper presents a series of successive plug-related tests completed in 2022-2023 in the Midland Basin. Initially, varied hydraulic fracturing designs were tested on two wells with permanent fiber optic cables. When stimulating these wells, the fiber optic data indicated compromised plug isolation on multiple stages. An ultrasonic scan was performed post-cleanout to corroborate those findings, and the outcomes of both diagnostics spurred a series of follow-up plug trials. The primary objectives of this study are to discuss the collective fiber optic and ultrasonic findings, the isolation issues they revealed, some enlightening differences between the two datasets, and the subsequent measures taken to improve the business unit's plug choice and design.
Proppant and fluid allocation between clusters were ascertained via distributed acoustic sensing (DAS) data gathered during stimulation. These measurements were statistically assessed to compute the stimulation distribution efficiency (SDE) two ways, first with uniformity index (UI) and second with the proppant distribution metric (PDM). Only the stages deemed to have good isolation were compared with one another. To quantify the degree of isolation, proppant placement efficiency (PPE) was calculated for every stage. Furthermore, comprehensive hydraulic fracture profiles (HFP) that account for proppant misallocation due to isolation issues were derived by analyzing the cumulative DAS energy response for a given stage during both its treatment and the stimulation of the subsequent stage. Where possible, distributed temperature sensing (DTS) data was employed to help differentiate between through-pipe and behind-pipe interstage communication. For the ultrasonic scans, a casing-wall loss percentage threshold was employed as the primary plug performance metric. When testing alternative plug options, static plug pressure tests were conducted at the surface prior to perforation. Drillout times were also assessed.
In the wells with fiber optics, the dissolvable plugs appeared to leak 77% of the time compared to 27% of the time for the composite plugs. Consequently, these groups had starkly different PPE values. When interstage communication was detected, it originated within the first 25% of the stage's treatment about 80% of the time, implying significant potential for proppant misallocation when isolation is compromised. Most lost isolation instances would not have been detectable with surface pressure and treatment rate plots. While all implemented diagnostics were helpful, fiber optics still provided the most accurate understanding of isolation. Through the deployment and joint assessment of fiber optics, ultrasonic imaging, static pressure tests, and operational key performance indicators (KPIs) across hundreds of stages and multiple developments, a couple plug choices with favorable isolation and operational outcomes were identified.
This work qualitatively and quantitatively evaluates SDE for different isolation conditions using DAS and DTS results. It also compares fiber optic readings and ultrasonic measurements for determining isolation efficacy. The analysis and conclusions here demonstrate the technical feasibility of using permanent fiber optics, ultrasonic imaging, and simple static pressure tests to identify and eventually mitigate poor plug performance. Collectively, these findings can be used to optimize future plug-and-perf completions strategies.
