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Abstract 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.
Grove, Brenden (Halliburton-Jet Research Center) | DeHart, Rory (Halliburton-Jet Research Center) | McGregor, Jacob (Halliburton-Jet Research Center) | Dennis, Haggerty (Halliburton-Jet Research Center) | Christopher, Chow (ProDuce Consulting)
Multiple perforation laboratory programs have been conducted during recent years to support high-pressure/ high-temperature (HP/HT) and ultrahigh-pressure (UHP) oil and gas field developments at various offshore locations globally. This paper highlights six such projects that supported activities within the Asia-Pacific, North Sea, and US Gulf of Mexico (GOM) (both Miocene and Lower Tertiary) regions. Each program was designed and conducted in collaboration with an operator and field operations personnel to help reduce potential risks, improve operational efficiency, and optimize well performance across a variety of challenging environments. Laboratory experiments were based on API RP 19B Sections 2 and 4, with test conditions customized to match specific downhole environments of interest (rock and fluid properties, stress, pressure, temperature, and flow scenarios). Matching downhole conditions at the laboratory proved important because this yields results that can be quite different from those obtained at surface (or scaled) test conditions. Reliable estimations of field perforation skin, sanding propensity, and the effectiveness of subsequent stimulation operations depend on realistic perforation and flow data obtained at relevant downhole conditions. The overriding goal for test design is to create and expose the laboratory perforation in an environment that matches its field counterpart as closely as possible. Beyond obtaining accurate flow data for skin and/or sanding propensity determination, post-test diagnostics, such as computed tomography (CT) and optical techniques, provide additional essential insight into the characteristics of the perforation tunnel, core interior, and the hole through the casing and cement. Results from these various programs were used to confirm or, in some cases, guide the field perforating strategy.
Abstract 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.
Abstract The performance of shaped charge jet perforators in complex downhole environments remains the status quo for successful cased-hole completions. Traditionally, these perforators have been evaluated using concrete targets under ambient conditions. The designs based on these evaluations were therefore optimized for conditions that don't reflect true downhole environments. Recent testing specifications in sandstone targets (API RP-19B Section 2) have also failed to consider the effects of complex well conditions and rock properties. In addition to the perforator itself, the overall completion design must be considered to properly optimize the perforating event. This is typically done using empirical correlations and first-order modeling software. While beneficial, these methods can misrepresent the complex interactions among the perforator, the reservoir, and the wellbore in the unique set of conditions. Ultimately, this can all lead to the deployment of a perforator optimized with conditions (not tailored to the reservoir) and utilizing generic practices, thereby leading to adverse implications on the overall well completion. The use of perforation flow laboratories and advances in shaped charge research and engineering have been employed in this study to understand and optimize shaped charge performance at downhole conditions. The perforators that result from a comprehensive test program in conjunction with multi-physics computational modeling are tailored for improved shaped charge performance under reservoir-specific conditions. These bespoke perforators undergo further testing as part of a more comprehensive optimization program to design the overall application on a well-specific basis. A similar scientific approach is also applied for the overall application optimization by integrating laboratory testing, CT imaging, computational flow dynamics, and dynamic event modeling to eventually upscale the results to the field applications. The results of these processes demonstrate the significant performance improvement in the shaped charge tailored for true reservoir conditions. Field applications examined in this study demonstrate specific uses of optimized perforators, as well as example workflows of how an integrated testing and modeling process can insure the perforators are applied properly. Comparisons demonstrate productivity improvements through these engineered processes. The new class of reservoir-driven shaped charges is aimed towards increasing production or injection by deeper formation connectivity with the wellbore as well as ensuring perforation contribution efficiency. The productivity gains in these case studies demonstrate the potential improvement in well completions through the use of engineered processes both for initial product design and specific application optimization in perforated completions.
Satti, Rajani (Baker Hughes) | Betancourt, David (Baker Hughes) | Harvey, William (Baker Hughes) | Zuklic, Stephen (Baker Hughes) | White, Ryan (Baker Hughes) | Ochsner, Darren (Baker Hughes) | Sampson, Tim (Baker Hughes) | Myers, William (Baker Hughes) | Gilliat, Jim (Baker Hughes)
Abstract Historically, the performance of shaped charge jet perforators has been evaluated using concrete targets under ambient conditions, thereby failing to clearly characterize their performance in downhole conditions. In recent years, testing using sandstone targets (API RP-19B Section 2) and various numerical models have been adopted as a better means of quantifying shaped charge performance. However, it is important to note that such testing and modeling methods do not still account for the complex shaped charge physics in downhole conditions, which includes pressures (wellbore to pore to confining), rock properties (bedding plane orientations, porosity, permeability, UCS, etc.), cement and casing material characteristics, etc. In fact, the results from standard tests or numerical models have been proven to be misleading while designing and optimizing shaped charges for reservoir conditions. As a result, the advent of perforation flow laboratories and advances in shaped charge research and engineering has been the key motivation for this work. In this work, we have employed a scientifically engineered approach to determine and optimize shaped charge performance. A comprehensive test program in conjunction with computational modeling was utilized to design, test and improve shaped charge performance under reservoir-specific conditions. For this purpose, methods relating to API RP-19B Section 4 testing and advanced hydrodynamic solvers were integrated into a scientific workflow. The results from this study demonstrate the following: First, pore pressure does influence shaped charge performance. Second, the best way to characterize the performance of a shaped charge is to conduct a laboratory test under true reservoir conditions. Third, designing a shaped charge around performance at true downhole conditions has enabled significant performance and productivity improvements. Utilizing advanced numerical modeling and extensive testing, we have achieved significant increase in shaped charge performance (penetration and flow area) in some of the most challenging reservoir conditions. The new class of reservoir-driven shaped charges is aimed towards increasing production or injection by deeper formation connectivity with the wellbore as well as ensuring perforation contribution efficiency.