In unconventional plays, the majority of horizontal well completions employ Plug and Perf methods using frac plugs to isolate multistage stimulation treatments. The post-stimulation operation typically consists of drilling out the plugs with coil tubing and commingling all frac stages. This operation can be costly and adds risk to the completion. Frac plug drill-ability and debris mitigation is a key factor in drill out efficiency. Recent advancements of dissolvable frac plug technologies have reduced or eliminated drill-outs and the cost of coil tubing intervention. This paper examines the effectiveness of dissolvable plug technology and its effect on drill-out operations.
The implementation of dissolvable frac plugs in full laterals was evaluated by several measures. Can the dissolvable plugs be milled if not fully dissolved? Does the dissolvable plug completely dissolve leaving a clean wellbore? Is there a time and cost benefit of cleaning a wellbore with 100% dissolvable plugs versus of a conventional, composite plug lateral? In an effort to evaluate dissolvables versus conventional composites, two trial wells were selected with the same stage count and lateral length. In one wellbore composite plugs were utilized throughout the entire lateral; in the second well, only dissolvable plugs were used. Both wells were drilled out using coiled tubing and the same BHA configuration. After the drill-outs, the total time in the well was compared to determine a time and cost savings.
The result of the trial proved that dissolvable plugs reduced drill-out times for each plug and reduced the total amount of coil tubing operations needed. A notable cost reduction and efficiencies were observed for thecoil tubing clean out operation due to high record-footage drill-out from surface to TD (Total Depth), and an efficiency gain during execution to bring the wells on to production. The dissolvable trial well showed the ability to eliminate short trips and minimize pumping sweeps, gels, and chemicals to clean out the hole. Use of the dissolvable plugs also resulted in quicker run-in hole times between each plug.
Coil tubing intervention is a legacy cost of Plug and Perf completions. Early frac plug technology required extensive drillout, and many plug design innovations have been directed at reducing the coil tubing cost. The advancement of dissolvable plugs presents the opportunity to reduce or eliminate drillout intervention. Perhaps an even greater benefit will be enabling the design of longer lateral completions that are not constrained by the limited reach of coil tubing.