Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
Summary Sealing elements (SEs) of fracture plugs have crucial roles to isolate target zones of a well in hydraulic fracturing. If the zonal isolation by the SE is not adequate, it can result in erosion of the casing. To the best of the authors’ knowledge, the effect of casing deformation on sealing performance is not well researched or understood. To study the effect of casing deformation on sealing performance, finite element analysis (FEA) of SEs in oval casings was conducted in this study. Finite element simulation of a degradable fracture plug with three different casings ovalities (0%, 2%, and 5%) and three different SE designs (O-ring type, short type, and traditional long type) was conducted to evaluate deformation behavior and sealing performance of SEs in deformed casings. Contact pressure (CPRESS) on the casing by the SE after the plug was set in the casing and the risk of leakage were discussed and compared for each design. In the casing with 0% ovality, all the SE designs established contact with the inner surface of the casing when setting force was applied. However, for the O-ring-type design, the area in contact with the casing was small and it may result in leak and erosion in the actual well if there is a small dent or deformation on the casing. When there is ovality in the casing, the minor inside diameter (ID) has a smaller ID and the major ID has a larger ID compared to the nominal ID of the casing. In the casing with 2% and 5% ovality, neither O-ring-type SE (O-SE) nor short-type SE (S-SE) could contact the major ID of the casing and there was a gap between the inner surface of the casing and the SE. This gap can cause erosion of the fracture plug and casing when the fluid passes through the gap. In contrast, the traditional long-type SE (L-SE) contacted both major and minor IDs of the casing, and no gap was observed. This result indicates that there is a potential risk of insufficient isolation of target zones and erosion of casings in actual well conditions if fracture plugs with S-SEs are used. Because there are various types of fracture plugs with different SE designs, this study helps to select proper fracture plugs with good SE design and mitigate the risk of erosion of casings and plugs. As this study is based on FEA simulations, future demonstrations through experiments and field trials are needed.
Summary Sealing elements (SEs) of fracture plugs have crucial roles to isolate target zones of a well in hydraulic fracturing. If the zonal isolation by the SE is not adequate, it can result in erosion of the casing. To the best of the authors’ knowledge, the effect of casing deformation on sealing performance is not well researched or understood. To study the effect of casing deformation on sealing performance, finite element analysis (FEA) of SEs in oval casings was conducted in this study. Finite element simulation of a degradable fracture plug with three different casings ovalities (0%, 2%, and 5%) and three different SE designs (O-ring type, short type, and traditional long type) was conducted to evaluate deformation behavior and sealing performance of SEs in deformed casings. Contact pressure (CPRESS) on the casing by the SE after the plug was set in the casing and the risk of leakage were discussed and compared for each design. In the casing with 0% ovality, all the SE designs established contact with the inner surface of the casing when setting force was applied. However, for the O-ring-type design, the area in contact with the casing was small and it may result in leak and erosion in the actual well if there is a small dent or deformation on the casing. When there is ovality in the casing, the minor inside diameter (ID) has a smaller ID and the major ID has a larger ID compared to the nominal ID of the casing. In the casing with 2% and 5% ovality, neither O-ring-type SE (O-SE) nor short-type SE (S-SE) could contact the major ID of the casing and there was a gap between the inner surface of the casing and the SE. This gap can cause erosion of the fracture plug and casing when the fluid passes through the gap. In contrast, the traditional long-type SE (L-SE) contacted both major and minor IDs of the casing, and no gap was observed. This result indicates that there is a potential risk of insufficient isolation of target zones and erosion of casings in actual well conditions if fracture plugs with S-SEs are used. Because there are various types of fracture plugs with different SE designs, this study helps to select proper fracture plugs with good SE design and mitigate the risk of erosion of casings and plugs. As this study is based on FEA simulations, future demonstrations through experiments and field trials are needed.
The Longmaxi shale gas play in Sichuan, China is unique due to multiple tectonic deformations in the geological history, which makes the shale play highly heterogenous and hydraulic fracturing execution problematic. The hydraulic fracturing design has matured after ten years’ evolution. However, it could not ensure every well's success without considering heterogeneity. Screenout, fracture hits, and casing deformation are still very common because informed decisions cannot be made ahead of operation or in real time. These risks should be recognized and in turn mitigation measures could be proposed through deep understanding of the geological and geomechanical characteristics. To address these challenges, a multidisciplinary team was formed to work on a pad. The geological and geomechanical (G&G) context was first determined by 3D G&G modeling. Then a survey was completed on the whole block to determine the root causes of screenout, frac hits, and casing deformation, and high-risk areas or stages were identified. Based on this, the proposed mitigation included adjusting perforation design, pump rate, fluid volume, and fracture sequence. The effectiveness of mitigation measures and the 3D G&G model were validated and iterated by onsite fracturing diagnostics. Through the above efforts, the designed proppant volume achieved zero casing deformations, fewer screenouts, and weaker fracture hits. This was the first pad with zero casing deformations across the whole block. The key findings were proved to be effective and could ensure success of hydraulic fracturing in the study pad of ultradeep Longmaxi Shale: The natural fracture corridors were the main cause of screenout. The possible bedding plane open and bad fracture initiation could be other causes of screenout. The natural fracture was the main cause of fracture hit and the connection among hydraulic fractures was the second cause. Adjusting the zipper fracturing sequence to interfere with hydraulic fracture propagation could help weaken it. Unstable natural fracture was the main causes of casing deformation in the Luzhou Block. Adjusting the fracturing sequence and fluid pumping intensity could mitigate casing deformation. The key to effective mitigation was continuous 3D G&G modeling through ongoing iterations with field data. Finally, a model-driven workflow was developed for hydraulic fracturing design and execution, which could be a resource for other shale plays with similar challenges worldwide.
The objective of this paper is to provide a review of casing deformations that are related to the placement of Multi-Stage Hydraulic Fracturing (MSHF) in unconventional plays. This work aims to identify practical mitigation and management strategies to reduce the overall impact of such events on the economic outcome of any development. The methodology incorporates a comprehensive literature review and leverages insights from the authors’ extensive field experience. This approach aims to explore the current state of knowledge regarding casing deformations associated with MSHF in unconventional reservoirs across key global basins. This paper encompasses the identification, diagnostics, surveillance, and monitoring of such deformations as they manifest and progress, along with the implementation of mitigation and management strategies prior to and during the well-completion process. The authors recognize the disparity between the number of publications available and the actual incidence of casing deformation in specific basins and are conscious that obtaining an exact estimate may often be elusive. The technical aspects of the review rely on the examination of numerous case studies from various unconventional basins. This is achieved by establishing a comprehensive understanding of the potential causes and mechanisms of casing deformations, including their occurrence, detection, and identification. Subsequently, an analysis is performed that presents the inherent characteristics of the different types of casing deformation, encompassing their nature, severity, distribution, and frequency across the basins considered, their lateral locations, event occurrence, specific nature and other pertinent factors. Additionally, the review addresses the geological, geo-mechanical, engineering and operational control factors that are likely to contribute to such deformations. Furthermore, it identifies a range of potential mitigation strategies aimed at minimizing the occurrence and ultimately the economic effects of casing deformation occurrence. This review builds upon various ongoing industry technical initiatives undertaken by the SPE Well Integrity Technical Section - Casing Deformation Work Group. The study findings can potentially provide practical measures to manage and mitigate casing deformation in unconventional basins within horizontal wells, thus minimizing the associated economic impact. Remaining knowledge gaps that require consideration should be addressed by actively sharing best practices and case histories within the industry on a global scale. This collaborative review paper, involving operating companies and other experts, serves as an initial step in that direction, aiming to catalyse further discussion among professionals working in this sector. It is intended as a rallying cry to encourage broader participation, deeper and shared consideration of the considerable effects of casing deformation occurrence.
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.