This presentation covers the essential elements of limited entry treatment design and reviews a case study of plug-and-perf horizontal well treatments in an unconventional shale play. In the case study, various diagnostic methods were used to better understand and quantify the factors determining limited entry effectiveness. Three diagnostic methods were implemented: 1.) injection step-down tests and pressure analysis of the fracturing treatments, 2.) video-based perforation imaging and 3.) distributed acoustic sensing (DAS).
In-situ stress variation and perforation erosion were determined to have significant impacts on treatment allocation among perforation clusters. Other undesirable effects such as heel-side flow preference were also observed. Camera images confirmed proppant-induced erosion at the scale of individual perforations. Measurements from the digital images provided comparison points for predictive software using surface pressure measurements. DAS results provided cluster level proppant distribution values. Correlations were also observed between treatment allocation values from DAS data and values derived from perforation friction calculated from Bernoulli’s equation using the image-based entry hole diameter data.
The results of the case study indicated that a staggered perforation design using more gradual changes among clusters would lead to a more balanced treatment. This scenario was evaluated along with a job design featuring high excess perforation friction and an equal number of perforations in each cluster. Fracture-simulation runs indicated that both tactics are likely to improve slurry allocation.
The key take-away from this lecture is that limited entry treatments can result in effective stimulation along the entire wellbore when the best practices disclosed in the presentation are followed.