Methods Improve Stimulation Efficiency of Perforation Clusters in Completions

Abstract

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.

Fiber-optic Monitoring: Stimulation Results from Unconventional Reservoirs

“…This type of approach is gaining credibility in the industry, not only for refracturing but also initial well completions (Ingram et al, 2014). Further analysis must be completed to understand how real-time diversion approaches impact these results.…”

Restimulation Design Considerations and Case Studies of Haynesville Shale

“…This makes it more difficult to initiate a fracture in some clusters relative to others being treated within the same stage. The second challenge is known as stress shadowing, in which the tightly spaced multiple clusters interfere with one another causing reduced fracture widths of some and thus unevenly created fracture geometry (Ingram et al 2014). …”

How will treatment parameters impact the optimization of hydraulic fracturing process in unconventional reservoirs?

“…Hydraulic fracturing is a very complex technique, and it is still not fully understood till date. Furthermore, the number of stages, length of fracture clusters in each stage, proppant and fracturing fluid compatibilities, optimum spacing length, proppant transport and placement, proppant and frac-fluid compatibility, and optimum spacing are some of the challenges inhibiting successful application of this technique across the world [7][8][9]. In addition, the interactions between propagating hydraulic fractures and in-situ pre-existing natural fractures hinder successful hydraulic fracturing process, thereby and causing failure of the in-situ rock along its weakest plane.…”