Preexistent Sleeve Nozzle Design for Targeted Planar Propagation as a Counter to Stress Shadowing in Hydraulic Fracturing
Authors: Watkins T. , Najafov J. , Watson E. K. , Livescu S. 
Published: October 2023

Fracturing bedrock formations using a pressurized fluid to increase hydrocarbon production has been around since 1866 (Hicks 2013). It has been used in unconventional formations for over six decades since George Mitchell started using it for shale formations (New York Times 2013). For most wells in North America, hydraulic fracturing is usually performed by plug-and-perf (Lehr 2021). To reduce operational complexity, time, and cost time and meet Environmental, Social, and Governance (ESG) goals, operating companies are in a continuous search for alternative innovative fracturing systems. A new approach to traditional hydraulic fracturing was recently presented, together with several case histories from Texas, the U.S., and Alberta, Canada, showing significantly improved project economics and lower environmental impact (Watkins et al. 2023a, b).

Plug-and-perf uses a perforating shape charge gun (Simpson 2017) to trigger charges to create channels through the casing into the adjacent rock formation (Renpu 2011). When the downhole plug seals the well, the high-pressure fracturing fluid is diverted into the channels to fracture the shale formation. While the plug-and-perf method has successfully increased hydrocarbon production, there are areas that can be improved. One key area overdue for efficiency improvement is the perforation cluster efficiency (PCE) of the fracture formation since it is estimated that one-third of perforation clusters fail to extend and have low production efficiencies (Miller et al. 2011; Wheaton et al. 2014). A key problem is stress shadows (Nagel. 2015; Wang et al. 2022), where stresses play a considerable role in fracture formation.

Perforations are placed in areas that the producers believe will result in maximum production, but the fracture propagates following underground conditions. This is typically away from earlier fractures. Consequently, the more stages near one another, the more skewed the stress shadows and the more inefficient the well due to the poor fracture network. If stress shadowing can be neutralized, it is likely that a well’s estimated ultimate recovery (EUR) or lifetime production could be one-third greater, given around half of all perforations do not propagate (see Fig. 1 cf. Miller et al. 2011; Wheaton et al. 2014). The magnitude of the problem, especially considering the current ESG trend, means companies should investigate ways to enhance resource extraction—especially if it can be done without incurring additional operating expenses.

Figure 1 Many perforations do not propagate, and a minority produces most of the production (Bere 2020; Rahim 2017).

A fracture follows the path of least resistance. When conventional perforating guns trigger a fracture, they "create long spiral-patterned perforations that leave the formation undertreated because fluid and proppant tend to flow and settle below the wellbore. Multiple spiral perforations also create competing fractures near the well that impede proppant and fluid penetration during treatment." (Dailey 2002; Li et al. 2022). This creates a bottom-heavy three-dimensional pattern that does not fully leverage the placement of the clusters within the target stage.

This paper explores a newly developed and field-deployed technology that produces very long fractures in a two-dimensional pattern within a single plane in both limited entry and single-point entry fracturing. This new fracturing system described previously (Watkins et al. 2023a, b) becomes a more efficient alternative to traditional plug-and-perf technology. This process forces fractures to stay in the targeted locations much further to significantly reduce the tendency for a fracture to intrude into adjacent fractures. The net result of keeping fractures within a single plane is a higher EUR over a well’s lifetime for a given unit of fracturing costs since the fractures form in the ideal locations that the producers identified beforehand. In addition, the new technology utilizes much lower carbon emissions during completions than plug and perf, especially when cradle-to-grave CO2 emissions are considered.