Technology Update Horizontal shale wells present the challenge of generating large, high-density fracture networks, reflecting the submicrodarcy permeability of the formations drilled by these wells. The goal is to create the largest fracture network volume to maximize ultimate recovery, because the fracture network volume in these wells has been shown to correlate strongly with the production level. However, as the network becomes too large for a given wellbore access point, the relative benefit of size diminishes. This is because of the low fracture conductivity, which creates large pressure drops within the network and makes it difficult to drain distant portions. And the effect is exacerbated by the inability to move water or liquid hydrocarbon through a large complex network (Mayerhofer et al. 2006). Thus, it is very important to create an optimal number of conductive transverse fractures or access points that intersect the wellbore. Today’s unconventional wells incorporate wellbore planning and completion designs that are based on the reservoir-specific characteristics needed for optimal drainage and field development. The key elements of the design and planning process must be carefully considered. They are well spacing, lateral length, the number of stages, the length of isolated stages, and the number of perforation clusters per stage. The strategies used are based in part on advancements in reservoir simulation, reservoir modeling, and production correlations from trial and error that stem from the initial work in various plays, except the relatively unique Barnett shale. Progress in Shale Completion Designs A good example of this progression toward more reservoir-specific completion designs was seen in the Haynesville shale. The play saw a rapid rampup in activity from 2009 to 2012 with peak completion activity occurring in mid-2011. By November 2011, it had reached its highest production level of 7.2 Bcf/D (EIA 2014). This dramatic rise in production was in part due to the optimization of completion and stimulation designs, particularly the reduction of the isolated length of each stage (plug-to-plug distance) and, thus, an increase in the number of stages per foot of lateral. The average daily gross perforated interval per stage (top perforation to bottom perforation) that Halliburton completed in the Haynesville and Bossier shales from 2010 to 2013 was analyzed. The data encompasses nearly 11,000 stages for more than 30 operators. It illustrates that many operators began to reduce their gross perforated interval per stage across the play by the middle of 2011. In July 2011, it was 272 ft and by mid-2012, it declined to 150 ft, falling at a relatively constant rate as operators increasingly went to a shorter isolated stage interval. This indicates closer stage spacing (plug to plug) or more stages per well, with lateral length remaining relatively constant. These trends continued into 2012 and a dramatic improvement was seen not only in the slope of the projected production decline curve, but also in the estimated ultimate recovery (EUR) for the wells being brought online.
This paper discusses design considerations to increase the estimated ultimate recovery (EUR) on underperforming wells in a refracturing scenario. A method for, and case histories of, using an environmentally acceptable, self-removing particulate diverter that has proven to be successful in the refracturing efforts of horizontal unconventional reservoirs are provided. This method is typically chosen for its low cost, self-assembly, and self-removal. An outline of the design process for refracturing and post-refracturing procedures is included. The ability to add reservoir contact, restore conductivity, remediate blockage, and address depleted reservoir pressure make this technique desirable. Different strategies can be applied when using this technique and are typically customized to the particular candidate well selected for the refracturing treatment. The treatment designs for the wells discussed in this paper were designed to increase EUR. Candidate wells for refracturing typically fall into one or more categories: understimulation occurred in the original completion, production damaging mechanisms are present, a low investment lease retention strategy was originally required, or a pressure-sink mitigation strategy is necessary for infill completions. Candidates in this paper fall into the understimulated category. A typical procedure consists of casing inspection, wellbore cleanout, possible addition of perforations, and flowback considerations. In this study, different Haynesville shale refracturing treatments, results, and diagnostics are compared. The evolution of treatment design components, such as carrier fluid, fluid volume, proppant volume, and diverting methodology, is explained. The results and underlying theory of these changes are outlined. Pre/post-treatment production is compared, along with treatment pressure trend analysis and microseismic data. Although performing secondary stimulation treatments is becoming more common, the industry's focus on improving production decline curves has led to a surging interest in refracturing horizontal unconventional reservoirs. Decline rates in unconventional reservoirs tend to be more rapid compared to conventional reservoirs because of their ultralow permeability, limited reservoir contact, and original completion strategy. Refracturing of these reservoirs enables the recovery of hydrocarbons trapped by these restrictions.
This paper discusses a method for, and case histories of, using an environmentally acceptable, selfremoving particulate diverter that has proven to be successful in the refracturing efforts of horizontal unconventional reservoirs. This method is typically chosen for its low cost, self-assembly, self-removal, and ease of addition into treatment. An outline of the evolution of restimulation design, typical procedures, and candidate selection strategies is provided. The ability to add reservoir contact, restore conductivity, and remediate blockage makes this technique desirable. Different strategies can be applied when using this product and are typically customized to the particular candidate well selected for the refracturing treatment. The treatment design is also often customized to the particular candidate well; however, key components of the design are outlined. Candidate wells for refracturing typically fall into one or more categories:• Understimulation occurred in the original completion.• Production damaging mechanisms are present. • A low investment lease retention strategy is required. • A pressure-sink mitigation strategy is necessary for infill completions.A typical procedure will consist of casing inspection, wellbore cleanout, addition of perforations, and flowback considerations.In this study, different Haynesville shale refracturing treatments and results are compared. The evolution of treatment designs, such as carrier fluid, fluid volume, proppant volume, and diverting methodology, are explained. The results and the theory behind these changes are outlined, along with the economic viability of refracturing treatments. Pre/post-treatment estimated ultimate recovery (EUR) calculations are compared, along with treatment pressure trend analysis. The EUR uplift from the refracturing treatments is used to show the economic viability.Although performing secondary stimulation treatments is not uncommon, the industry's focus on improving production decline curves has led to a surging interest in refracturing horizontal unconventional reservoirs. Decline rates in unconventional reservoirs tend to be more rapid compared to conventional reservoirs because of their ultralow permeability, limited reservoir contact, and original completion strategy. Restimulation of these reservoirs enables the recovery of hydrocarbons trapped by these restrictions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.