API RP 19B Section 2 Perforation Tests Conducted at Multiple Facilities to Guide the Latest Section 2 Revision

SPE Annual Technical Conference and Exhibition

Manning

2018

Explosive perforating has been the dominant method of establishing communication between the reservoir and cased wellbore for more than 70 years. Effective perforations, which provide an unimpeded flowpath, are critical to deliver the well performance required to justify overall project investment. To reliably estimate or predict well flow performance, it is essential to have an accurate understanding of critical perforation parameters that exist downhole, including tunnel penetration depth into the formation, cleanness of the tunnels, and hole diameter through the casing. Consequently, the industry has focused significant attention toward developing this understanding in recent decades. This is particularly true today, as downhole environments are becoming more extreme. Project investment decisions require increasingly accurate well performance estimates, both initially and over the life of a development. This current state of affairs has motivated a recent and ongoing effort to better understand perforator performance at full downhole conditions, up to and exceeding 30,000 psi. A large program is underway to investigate the penetration and hole size performance of several charges across a range of rocks and pressure conditions. The goal of this program is to obtain fundamental insights into the effects of extreme values of certain downhole conditions on perforator performance. The current test program follows the recently revised API-RP 19B Section II protocol and includes high-pressure variations of the standard test configuration. One area of key findings thus far is in the context of recent industry frameworks for analyzing laboratory penetration data, including ballistic stress and the ballistic indicator function. These are found to be useful tools that simplify analysis and provide insight and guidance. These frameworks make it possible to collapse multiple diverse penetration datasets, from across a range of test conditions, toward a single performance curve. This curve can be used to enable ballpark estimates of the performance of a given charge in a specific rock strength and stress regime. It provides the potential to identify a penetration asymptote (assumed to be a fundamental charge property that would be observed in very strong and/or highly-stressed rocks). It is also a useful framework to quickly visualize a vast spectrum of reservoir conditions, and to identify where a specific reservoir may fit in the broader context. Of particular interest to the perforating testing community is the relatively narrow range of values encompassed by the newly-revised API-RP 19B Section II standard test conditions. To extend this framework to predictive models of charge penetration over a broad range of downhole conditions, however, study results indicate that more work is needed. It will be necessary, for example, to account for charge-dependent wellbore effects to move closer to a predictive capability that exhibits the level of quantitative accuracy required for many applications. Other fundamental findings involve wellbore pressure influence on perforator performance. For one charge studied somewhat extensively, wellbore pressure was observed to exhibit an interesting non-monotonic influence on penetration. Moderate wellbore pressures increased penetration depth; higher wellbore pressures decreased penetration depth. Wellbore fluid pressure was also found to exhibit a charge-dependent influence on casing hole size performance; increasing wellbore pressure tended to reduce the hole size slightly for one charge tested, but had no effect for two other charges tested.

Shaped Charge Perforation Depth at Full Downhole Conditions: New Understandings

SPE Annual Technical Conference and Exhibition

Manning

2018

Perforation Damage, Cleanup, and Inflow Performance: Advances in Diagnostics and Characterization

SPE Middle East Oil and Gas Show and Conference

Grader

Derzhi

et al. 2019

Considering the important role that perforation laboratory testing can play in establishing field completion strategies, and thus ultimately well performance, efforts are currently underway to further strengthen the link between laboratory results and field well performance predictions. Some of these efforts focus on integrating advanced diagnostic and computational tools (namely computed tomography (CT), and pore-scale flow simulation) into the perforation testing workflow. This integration enables local variations in permeability and porosity to be identified and quantified, thus improving the interpretation of perforation laboratory results, and ultimately the translation of these results to the downhole environment. CT techniques have been used for core analysis, characterization, and flow visualization since the early 1980s. By the early 1990s, these techniques were being applied to the investigation of laboratory-perforated cores to enhance the interpretation of tests conducted following API RP19B Section 2 or 4. This application has increased dramatically since 2012, following the installation of a CT scanning system on-site at a perforating laboratory facility. As a result, this non-destructive technique has become a preferred method to routinely characterize perforation tunnels and the surrounding rock, as well as to enable the repeated inspection of a perforated core at multiple steps throughout a test sequence designed to mimic field operations scenarios. Coinciding with this development has been the advancement and application of micro-CT technology to better understand pore-scale phenomena, both near and away from the perforation. This paper introduces an integrated test program currently underway and summarizes key results from two experiments in which stressed rock targets were perforated under significantly different conditions. The first experiment involved perforating a moderate strength sandstone core under conditions that retained substantially all perforation damage, thus preserving the "crushed zone". Micro-CT analysis of different locations within the crushed zone region revealed significant compaction, with porosity reductions ranging from 10 to 50% below that of the native rock. Permeability at one of these selected locations was determined and found to be reduced by approximately 35% below the native rock value. The second experiment involved perforating a very high-strength sandstone core under conditions intended to produce full cleanup. CT and micro-CT analysis revealed fine fractures near the tunnel tip and confirmed the near-complete removal of the perforation damage, with only a very thin (less than 1 mm) compacted zone remaining at the tunnel wall. Although this region is interpreted to have very low permeability (as indicated by the near-zero connected porosity detectable at the resolution investigated), a fracture network combined with the shell’s minimal thickness suggests that this would provide a minimal impediment to inflow. Ongoing work aims to expand these findings and capabilities. A main effort going forward centers on simulating core-scale perforation inflow, incorporating the localized rock property variations determined as described in this paper. Additional property variations away from the perforation (for example, natural heterogeneity and/or anisotropy that often exist in reservoir wellcore samples) will also be taken into account. Such localized variations, both near and away from the perforation, are generally not taken into account in typical Section 4 test programs. Consequently, this ongoing effort will ultimately strengthen the relevance of Section 4 results to the downhole environment.

Frac Charge Performance at Downhole Conditions: Assessments and Implications

Day 3 Thu, May 06, 2021

McGregor

DeHart

et al. 2021

Hydraulically fractured completions dominate industry perforating activity, particularly in North American land basins. This has led to the development of fracture-optimized perforating systems in recent years. Aside from overarching safety, reliability, and efficiency priorities, the main technical performance attribute of these systems is consistent hole size in the casing, driven by limited entry fracture design considerations. While the industry continues to seek further improvements in hole size consistency, attention is also being directed to the perforations more holistically, from a perspective of maximizing the effectiveness of subsequent hydraulic fracturing and ultimately production operations. To this end, this paper presents two related activities addressing the development, qualification, and optimization of perf-for-frac systems. The first is a surface testing protocol used to characterize perforating system performance, in particular casing hole size and consistency. The second is a laboratory program, recently conducted to investigate perforating stressed Eagle Ford shale samples at downhole conditions. This program explored the influences of charge size, formation lamination direction, pore fluid, and dynamic underbalance on perforation characteristics. Casing hole size was also assessed. For the first activity (surface testing), we find that using cement-backed casing can be an important feature to ensure more downhole-realistic results. For the second activity (laboratory program), perforation casing hole sizes for the charges tested were in line with expectations based on existing surface test data, exhibiting negligible pressure dependency. Corresponding penetration depths into the stressed shale samples generally ranged from 3.5-in to 5-in, which is much shallower than might be expected based on surface concrete performance. Dynamic underbalance was found to exhibit some slight effect on the tunnel fill characteristics, while pore system fluid was found to have minimal influence on the results. An interesting feature of the perforated samples was the complex fracture network at the perforation tips, which appeared "propped" to some extent with charge liner debris. Some of these fractures were formation beds which had delaminated during the shot, a phenomenon observed for perforations both parallel and perpendicular to the laminations. The implications of these results to the downhole environment continues to be assessed. Of particular interest is the impact these phenomena might have on fracture initiation, formation breakdown, and treatment stages which accompany subsequent hydraulic fracturing pumping operations.