The Experts below are selected from a list of 201 Experts worldwide ranked by ideXlab platform
Saeed Salehi - One of the best experts on this subject based on the ideXlab platform.
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Numerical modeling and experimental study of elastomer seal assembly in downhole wellbore equipment: Effect of material and chemical swelling
Polymer Testing, 2020Co-Authors: Shawgi Ahmed, Harshkumar Patel, Saeed SalehiAbstract:Abstract Seal assemblies are critical elements in a variety of drilling and completion equipment such as wellhead casing Hangers, packers, and Liner Hangers. Zonal isolation is accomplished by seal compression (energization) which generates contact pressure at the seal-pipe interface. The performance of a seal is evaluated based on its mechanical and hydraulic integrity as well as its resistance to failure mechanisms. Objective of this study is to evaluate the performance of a seal assembly at varying compressions, seal and pipe properties, and chemical swelling. In this paper, numerical modeling approach validated by a lab-scale experimental work has been presented. Finite element model and experimental setup consisting of Liner, casing, compression plates, and elastomer seal are used. In the model, seal performance was evaluated in terms of contact pressure generated at seal-pipe interface. Experimental setup was used to verify the modelling results. In experiments, sealability was evaluated by injecting gas and observing leakage. Modelling results indicate that elastomer sealability is linearly dependent on amount of seal compression. Numerical model also demonstrated that pipe material can have notable impact on elastomer sealability. Simulation results show that seal-pipe friction has insignificant impact on seal performance. Exposure to surfactant caused volumetric swelling of investigated elastomer materials. Despite reduction in hardness, volumetric swelling was high enough to generate additional seal compression and provide improved sealability as demonstrated by model. Performance evaluation of Liner Hangers is considered a challenge for industry and regulators because of limited testing protocols, standards, or regulatory guidelines for evaluating this type of barrier system. Information generated in this work will help further advance performance evaluation and qualification guidelines for Liner Hanger seal assembly.
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review of gas migration and wellbore leakage in Liner Hanger dual barrier system challenges and implications for industry
Journal of Natural Gas Science and Engineering, 2020Co-Authors: Shawgi Ahmed, Saeed Salehi, Chinedum Peter EzeakachaAbstract:Abstract Robust dual barrier systems are crucial for well integrity. Regulators and industry have consistently raised the concerns in such systems regarding the leak pathways and its failure modes prediction, testing, and qualification. Liner Hanger is an example of dual barrier system in which seal assembly and cement sheath act as two barrier elements. The Liner Hanger system is usually employed in complex operating environments such as high-pressure and high-temperature (HPHT), deep-water, and ultra-deep-water. In these harsh environments, the gas migration through such system has been attributed to several well control incidents. To investigate this problem, a thorough review of underlying complexities, leakage mechanisms, Liner Hanger seal assembly materials, dominant failure mechanisms in seal and cement, and the gap in current standards and regulations is conducted. Overall, the objective of this paper is to understand the nuances of the Liner Hanger dual barrier system and to identify the risks of failures that could compromise the wellbore integrity.
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Analytical and Experimental Investigation of the Critical Length in Casing–Liner Overlap
Sustainability, 2019Co-Authors: Mustafa Al Ramadan, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Offshore drilling operations exhibit various difficulties attributed to shallow flows worldwide. One of the most common practices for drilling offshore wells is to use Liners and Liner Hangers rather than using full casing strings. This reduces the cost of drilling operation. Liners and Liner Hangers are required to pass certain standards prior to their deployment in the field. This ensures their ability to withstand harsh downhole conditions and maintain the integrity of the well. A Liner Hanger contains an integrated seal assembly that acts as a barrier to prevent fluid migration. The cement that is placed within the casing–Liner overlap is also considered a barrier, and it is critical that it maintains the integrity of the well by mitigating fluid migration to other formations and to the surface. The failure of this dual barrier (cement and seal assembly) system to seal the annular space can result in serious problems that might jeopardize a well’s integrity. Typically, in field applications, the length of a casing–Liner overlap is chosen arbitrarily. In some cases, shorter overlaps (50 to 200 ft) are chosen because of the lower cost and easy identification of leaks during pressure tests. However, some loss of well control incidents (particularly the incident that motivated this study) have been linked to fluid leakages along the casing–Liner overlap. This paper investigates the critical length of the casing–Liner overlap by modeling gas leakage through the cement placed within the overlap using analytical and experimental approaches. Leakage scenarios were developed to mimic gas migration within the cement in the casing–Liner overlap. The results showed that the longer the casing–Liner overlap, the higher the leakage time. The results also showed that the current casing pressure test duration of 30 min may not be adequate to verify the integrity of the cement within the overlap. Based on the results and analyses, it is recommended to increase the pressure test duration to 90 min. In addition, the results suggest that the length of the casing–Liner overlap should not be less than 300 ft to maintain the integrity of the well in the case of gas influx. Further details are highlighted in the results section. In practice, the current rationale behind the selection of a casing–Liner overlap length is not sustainable. Thus, the major advantage of this study is that with field data, it provides both scientific and research-based evidence that can be used to inform the decision behind the selection of the casing–Liner overlap length, especially in gas migration-prone zones.
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Experimental investigation of well integrity: Annular gas migration in cement column
Journal of Petroleum Science and Engineering, 2019Co-Authors: Mustafa Al Ramadan, George Kwatia, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Abstract Cementing operations present various difficulties attributed to shallow flows all around the world. Cement ability to seal the annular space, aids in sustaining the well integrity by mitigating and preventing fluid migration to other formations and to surface. Failure of cement to seal the annular space can result in serious problems that might jeopardize the well integrity. In this study, a wellbore model setup was designed and fabricated to mimic the gas migration in cemented annulus. A series of experiments were conducted on this setup to examine the cement sealability of neat Class H and neat Class G cements, and to also evaluate the effect of anti-gas migration additive on the cement sealability. Different additives were used such as bentonite and latex. Experiments conducted revealed that neat Class H, Class G, and any other slurry design with additives (but without anti-gas migration additives) does not have the ability to serve in mitigating gas migration. The wellbore permeability of annular cement using neat Class H and Class G cement was ranging between 10−3 to 10−1 mD. In addition, it has been found that the wellbore permeability of annular cement increases as cement age increases. Annular cement should not be considered as the primary barrier when Liner-Hanger is used.
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evaluation of Liner Hanger seal assembly and cement sheath as a dual barrier system implications for industry standards
Journal of Petroleum Science and Engineering, 2019Co-Authors: Shawgi Ahmed, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Abstract Liner Hanger seal assembly and cement sheath are essential barrier elements for well drilling and completions. During installation, the Liner Hanger seal assembly is set up-stream to the cement column. This arrangement prevents the evaluation of both the Liner Hanger seal assembly and cement sheath independently. Currently, there are no testing procedures, industry standards, or regulatory guidelines for testing this type of dual barrier system independently. The primary objective of this study is to establish that cement sheath can act as a secondary barrier element in a dual barrier (elastomer seal and cement sheath) zonal isolation system, if the elastomer seal (primary barrier) is faulty. In the context of this study, the term "barrier" describes the use of cement sheath and elastomer sealing element in a Liner Hanger to prevent uncontrolled migration of formation fluid to a shallow formation or surface facilities. Another objective is to evaluate the effect of using an anti-gas migration additive on cement sealability. To achieve these objectives, experimental testing procedures were developed to evaluate the performance of a Liner Hanger seal assembly and cement sheath. Two experimental scenarios were considered in this study. The first scenario included testing faulty ethylene propylene diene monomer (EPDM) elastomer with neat Class H cement and the second scenario included testing faulty EPDM elastomer and Class H cement mixed with a commercial gas migration control additive. The tests were conducted at different pressures and wait on cement (WOC) intervals. The results revealed that neat Class H cement cannot act as a secondary barrier and prevent gas migration in the case that the primary barrier (elastomeric element of the Liner Hanger) is faulty. The cement slurry with the commercial gas migration control additive can act as a secondary barrier in case the primary barrier is faulty. The results also showed that WOC time improves cement sheath sealability. In addition, pipe material and surface roughness play key roles in the cement slurry bonding process. The major addition to the literature from this study is that for cement sheath to be considered a secondary barrier element in a dual barrier zonal isolation system, it must contain a specific anti-gas migration additive in addition to other cement additives. This specification should be included as a standard regulatory practice and should be adopted for every well section.
Weiqing Li - One of the best experts on this subject based on the ideXlab platform.
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Research on the Modification of the Tapered Roller of Rotating Liner Hanger Bearing Based on Hybrid Intelligence
2018 14th International Conference on Natural Computation Fuzzy Systems and Knowledge Discovery (ICNC-FSKD), 2018Co-Authors: Weiqing Li, Jiahua Wu, Man Zhang, Yuanbiao HuAbstract:The heavy load causes the roller end breakage of the rotating Liner Hanger bearing, which is one of the important reasons of bearing failure. This paper researches on the internal shape modification of the tapered roller of bearing to solve the edge effect and extend the bearing service life. Firstly, a Back Propagation (BP) neural network was established where inputs are the degrees of depth and hollow and outputs are the maximum contact stress between the roller and the shaft ring of the bearing under different depth and hollow and the maximum equivalent stress of the roller. Secondly, the genetic algorithm was applied to optimize the BP neural network structure to prevent it from falling into the local minimum and obtained the best modification parameters. At last, finite element method was applied to simulate the predicted result. The simulation results showed that edge effect disappeared and the maximum contact stress between the roller and the shaft ring and the maximum equivalent stress of the roller were greatly improved.
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Effect of Axis Misalignment on the Fatigue Life of the Rotary Liner Hanger Bearing
2018 37th Chinese Control Conference (CCC), 2018Co-Authors: Weiqing Li, Yuanbiao HuAbstract:In this paper, the influence of ring axis misalignment on the fatigue life of the rotary Liner Hanger bearing was analyzed. In order to predict the fatigue life, a load analysis model established by using quasi-static method was used to analyze the contact load distribution between rollers and rings under different axis misalignment angles. The contact stress distribution of rollers' generator which used to calculate the bearing's fatigue life was obtained by using the elastic half-space method, and its result was verified by using FEM method. Fatigue life of the rotary Liner Hanger bearing under different axis misalignment angles was calculated and the change rule of the bearing's fatigue life at different axis misalignment angles was obtained.
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ICNC-FSKD - Research on the Modification of the Tapered Roller of Rotating Liner Hanger Bearing Based on Hybrid Intelligence
2018 14th International Conference on Natural Computation Fuzzy Systems and Knowledge Discovery (ICNC-FSKD), 2018Co-Authors: Weiqing Li, Jiahua Wu, Man Zhang, Yuanbiao HuAbstract:The heavy load causes the roller end breakage of the rotating Liner Hanger bearing, which is one of the important reasons of bearing failure. This paper researches on the internal shape modification of the tapered roller of bearing to solve the edge effect and extend the bearing service life. Firstly, a Back Propagation (BP) neural network was established where inputs are the degrees of depth and hollow and outputs are the maximum contact stress between the roller and the shaft ring of the bearing under different depth and hollow and the maximum equivalent stress of the roller. Secondly, the genetic algorithm was applied to optimize the BP neural network structure to prevent it from falling into the local minimum and obtained the best modification parameters. At last, finite element method was applied to simulate the predicted result. The simulation results showed that edge effect disappeared and the maximum contact stress between the roller and the shaft ring and the maximum equivalent stress of the roller were greatly improved.
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Rotary Liner Hanger Bearing Roller Modeling and Modification Based on Solidworks Secondary Development
Proceedings of the 2015 International Conference on Modeling Simulation and Applied Mathematics, 2015Co-Authors: Weiqing Li, Jin XuAbstract:The main failure form of the rotary Liner Hanger bearing is roller end breakage in the drilling engineering. Some modification methods are applied to solve this problem, however, the modification formula is very complex and calculation process need to be repeated, which may lead to calculating negligence, and lower the accuracy of modification. In this paper, one rotating Liner Hanger bearing roller modification system is designed by applying Solidworks API functions, macro and VBA programming environment based on Solidworks secondary development platform and improved roller modification theory of rotating Liner Hanger bearing roller. With analyzing the working condition parameters, designing the modeling program, and designing interface and the result display module, a parameterized modeling and rapid modification of tapered roller system is achieved. This system greatly improved the efficiency and accuracy of the modeling and modification of roller, which provides some convenience for the subsequent research, analysis and manufacturing.
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finite element analysis on rubber sealing ring of the rotary Liner Hanger bearing
2015 International Conference on Modeling Simulation and Applied Mathematics, 2015Co-Authors: Weiqing Li, Yu Wang, Detian MiaoAbstract:Rotary Liner Hanger bearing will be wear sharply and decreased its service life if the sealing structure is not able to prevent the drilling fluid to enter into the bearing. A twodimensional finite element model of the self-designed nonstandard rubber sealing ring was carried out on the software of ABAQUS. The rules of deformation and stress for the sealing ring with different value of initial interference, working pressure and the deep-well temperature were studied. The result shows that the maximum contact stress increases with the increase of value of initial interference and the maximum contact stress is always bigger than the value of work pressure. The effect of deepwell high temperature on sealing performance is not obvious compared with normal temperature. The result of this study is able to be the basis of modifying the structure and improving the performance of sealing ring. Keywords-rubber sealing ring; non-linear finite element analysis; contact stress; sealing performance;thermo-mechanical coupling
Yuanbiao Hu - One of the best experts on this subject based on the ideXlab platform.
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Research on the Modification of the Tapered Roller of Rotating Liner Hanger Bearing Based on Hybrid Intelligence
2018 14th International Conference on Natural Computation Fuzzy Systems and Knowledge Discovery (ICNC-FSKD), 2018Co-Authors: Weiqing Li, Jiahua Wu, Man Zhang, Yuanbiao HuAbstract:The heavy load causes the roller end breakage of the rotating Liner Hanger bearing, which is one of the important reasons of bearing failure. This paper researches on the internal shape modification of the tapered roller of bearing to solve the edge effect and extend the bearing service life. Firstly, a Back Propagation (BP) neural network was established where inputs are the degrees of depth and hollow and outputs are the maximum contact stress between the roller and the shaft ring of the bearing under different depth and hollow and the maximum equivalent stress of the roller. Secondly, the genetic algorithm was applied to optimize the BP neural network structure to prevent it from falling into the local minimum and obtained the best modification parameters. At last, finite element method was applied to simulate the predicted result. The simulation results showed that edge effect disappeared and the maximum contact stress between the roller and the shaft ring and the maximum equivalent stress of the roller were greatly improved.
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Effect of Axis Misalignment on the Fatigue Life of the Rotary Liner Hanger Bearing
2018 37th Chinese Control Conference (CCC), 2018Co-Authors: Weiqing Li, Yuanbiao HuAbstract:In this paper, the influence of ring axis misalignment on the fatigue life of the rotary Liner Hanger bearing was analyzed. In order to predict the fatigue life, a load analysis model established by using quasi-static method was used to analyze the contact load distribution between rollers and rings under different axis misalignment angles. The contact stress distribution of rollers' generator which used to calculate the bearing's fatigue life was obtained by using the elastic half-space method, and its result was verified by using FEM method. Fatigue life of the rotary Liner Hanger bearing under different axis misalignment angles was calculated and the change rule of the bearing's fatigue life at different axis misalignment angles was obtained.
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ICNC-FSKD - Research on the Modification of the Tapered Roller of Rotating Liner Hanger Bearing Based on Hybrid Intelligence
2018 14th International Conference on Natural Computation Fuzzy Systems and Knowledge Discovery (ICNC-FSKD), 2018Co-Authors: Weiqing Li, Jiahua Wu, Man Zhang, Yuanbiao HuAbstract:The heavy load causes the roller end breakage of the rotating Liner Hanger bearing, which is one of the important reasons of bearing failure. This paper researches on the internal shape modification of the tapered roller of bearing to solve the edge effect and extend the bearing service life. Firstly, a Back Propagation (BP) neural network was established where inputs are the degrees of depth and hollow and outputs are the maximum contact stress between the roller and the shaft ring of the bearing under different depth and hollow and the maximum equivalent stress of the roller. Secondly, the genetic algorithm was applied to optimize the BP neural network structure to prevent it from falling into the local minimum and obtained the best modification parameters. At last, finite element method was applied to simulate the predicted result. The simulation results showed that edge effect disappeared and the maximum contact stress between the roller and the shaft ring and the maximum equivalent stress of the roller were greatly improved.
Shawgi Ahmed - One of the best experts on this subject based on the ideXlab platform.
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Numerical modeling and experimental study of elastomer seal assembly in downhole wellbore equipment: Effect of material and chemical swelling
Polymer Testing, 2020Co-Authors: Shawgi Ahmed, Harshkumar Patel, Saeed SalehiAbstract:Abstract Seal assemblies are critical elements in a variety of drilling and completion equipment such as wellhead casing Hangers, packers, and Liner Hangers. Zonal isolation is accomplished by seal compression (energization) which generates contact pressure at the seal-pipe interface. The performance of a seal is evaluated based on its mechanical and hydraulic integrity as well as its resistance to failure mechanisms. Objective of this study is to evaluate the performance of a seal assembly at varying compressions, seal and pipe properties, and chemical swelling. In this paper, numerical modeling approach validated by a lab-scale experimental work has been presented. Finite element model and experimental setup consisting of Liner, casing, compression plates, and elastomer seal are used. In the model, seal performance was evaluated in terms of contact pressure generated at seal-pipe interface. Experimental setup was used to verify the modelling results. In experiments, sealability was evaluated by injecting gas and observing leakage. Modelling results indicate that elastomer sealability is linearly dependent on amount of seal compression. Numerical model also demonstrated that pipe material can have notable impact on elastomer sealability. Simulation results show that seal-pipe friction has insignificant impact on seal performance. Exposure to surfactant caused volumetric swelling of investigated elastomer materials. Despite reduction in hardness, volumetric swelling was high enough to generate additional seal compression and provide improved sealability as demonstrated by model. Performance evaluation of Liner Hangers is considered a challenge for industry and regulators because of limited testing protocols, standards, or regulatory guidelines for evaluating this type of barrier system. Information generated in this work will help further advance performance evaluation and qualification guidelines for Liner Hanger seal assembly.
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review of gas migration and wellbore leakage in Liner Hanger dual barrier system challenges and implications for industry
Journal of Natural Gas Science and Engineering, 2020Co-Authors: Shawgi Ahmed, Saeed Salehi, Chinedum Peter EzeakachaAbstract:Abstract Robust dual barrier systems are crucial for well integrity. Regulators and industry have consistently raised the concerns in such systems regarding the leak pathways and its failure modes prediction, testing, and qualification. Liner Hanger is an example of dual barrier system in which seal assembly and cement sheath act as two barrier elements. The Liner Hanger system is usually employed in complex operating environments such as high-pressure and high-temperature (HPHT), deep-water, and ultra-deep-water. In these harsh environments, the gas migration through such system has been attributed to several well control incidents. To investigate this problem, a thorough review of underlying complexities, leakage mechanisms, Liner Hanger seal assembly materials, dominant failure mechanisms in seal and cement, and the gap in current standards and regulations is conducted. Overall, the objective of this paper is to understand the nuances of the Liner Hanger dual barrier system and to identify the risks of failures that could compromise the wellbore integrity.
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evaluation of Liner Hanger seal assembly and cement sheath as a dual barrier system implications for industry standards
Journal of Petroleum Science and Engineering, 2019Co-Authors: Shawgi Ahmed, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Abstract Liner Hanger seal assembly and cement sheath are essential barrier elements for well drilling and completions. During installation, the Liner Hanger seal assembly is set up-stream to the cement column. This arrangement prevents the evaluation of both the Liner Hanger seal assembly and cement sheath independently. Currently, there are no testing procedures, industry standards, or regulatory guidelines for testing this type of dual barrier system independently. The primary objective of this study is to establish that cement sheath can act as a secondary barrier element in a dual barrier (elastomer seal and cement sheath) zonal isolation system, if the elastomer seal (primary barrier) is faulty. In the context of this study, the term "barrier" describes the use of cement sheath and elastomer sealing element in a Liner Hanger to prevent uncontrolled migration of formation fluid to a shallow formation or surface facilities. Another objective is to evaluate the effect of using an anti-gas migration additive on cement sealability. To achieve these objectives, experimental testing procedures were developed to evaluate the performance of a Liner Hanger seal assembly and cement sheath. Two experimental scenarios were considered in this study. The first scenario included testing faulty ethylene propylene diene monomer (EPDM) elastomer with neat Class H cement and the second scenario included testing faulty EPDM elastomer and Class H cement mixed with a commercial gas migration control additive. The tests were conducted at different pressures and wait on cement (WOC) intervals. The results revealed that neat Class H cement cannot act as a secondary barrier and prevent gas migration in the case that the primary barrier (elastomeric element of the Liner Hanger) is faulty. The cement slurry with the commercial gas migration control additive can act as a secondary barrier in case the primary barrier is faulty. The results also showed that WOC time improves cement sheath sealability. In addition, pipe material and surface roughness play key roles in the cement slurry bonding process. The major addition to the literature from this study is that for cement sheath to be considered a secondary barrier element in a dual barrier zonal isolation system, it must contain a specific anti-gas migration additive in addition to other cement additives. This specification should be included as a standard regulatory practice and should be adopted for every well section.
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Experimental investigation of elastomers in downhole seal elements: Implications for safety
Polymer Testing, 2019Co-Authors: Shawgi Ahmed, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Abstract One of the multiple barriers that is installed in the downhole during drilling and completion is the Liner Hanger seal assembly. The Liner Hanger is used to engage the Liner, connect it to the previous casing, and seal off with cement before a pressure test is performed. Verifying the sealability of the elastomeric element in a Liner Hanger is a critical factor for well integrity. In this study, the performance verification process and tests were conducted based on critical reviews of literature, current regulations, and applicable industry standards. The objectives of this experimental study are to develop testing protocols to investigate the performance of common elastomeric seals that are used in a Liner Hanger seal assembly. Ethylene propylene diene monomer (EPDM) and nitrile butadiene rubber (NBR) were selected for the tests because they are commonly used in downhole sealing systems. The results from the experiments revealed that the elastomeric seals did not exhibit any leakage when they were subjected to a pressure test of 40 psig (275.79 kPa) under normal conditions. The sealing performance of EPDM and NBR after surfactant degradation was not impaired for the test conditions used in this study. However, both elastomers failed the pressure tests and leaked when a mechanical defect was intentionally created and after exposure to carbon dioxide. The pressure cycling results showed that elastomers energization plays a critical role in maintaining their seal integrity. The results also showed that prolonging the pressure test duration from 30 to 60 min did not affect the elastomers performance.
Chinedum Peter Ezeakacha - One of the best experts on this subject based on the ideXlab platform.
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review of gas migration and wellbore leakage in Liner Hanger dual barrier system challenges and implications for industry
Journal of Natural Gas Science and Engineering, 2020Co-Authors: Shawgi Ahmed, Saeed Salehi, Chinedum Peter EzeakachaAbstract:Abstract Robust dual barrier systems are crucial for well integrity. Regulators and industry have consistently raised the concerns in such systems regarding the leak pathways and its failure modes prediction, testing, and qualification. Liner Hanger is an example of dual barrier system in which seal assembly and cement sheath act as two barrier elements. The Liner Hanger system is usually employed in complex operating environments such as high-pressure and high-temperature (HPHT), deep-water, and ultra-deep-water. In these harsh environments, the gas migration through such system has been attributed to several well control incidents. To investigate this problem, a thorough review of underlying complexities, leakage mechanisms, Liner Hanger seal assembly materials, dominant failure mechanisms in seal and cement, and the gap in current standards and regulations is conducted. Overall, the objective of this paper is to understand the nuances of the Liner Hanger dual barrier system and to identify the risks of failures that could compromise the wellbore integrity.
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Analytical and Experimental Investigation of the Critical Length in Casing–Liner Overlap
Sustainability, 2019Co-Authors: Mustafa Al Ramadan, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Offshore drilling operations exhibit various difficulties attributed to shallow flows worldwide. One of the most common practices for drilling offshore wells is to use Liners and Liner Hangers rather than using full casing strings. This reduces the cost of drilling operation. Liners and Liner Hangers are required to pass certain standards prior to their deployment in the field. This ensures their ability to withstand harsh downhole conditions and maintain the integrity of the well. A Liner Hanger contains an integrated seal assembly that acts as a barrier to prevent fluid migration. The cement that is placed within the casing–Liner overlap is also considered a barrier, and it is critical that it maintains the integrity of the well by mitigating fluid migration to other formations and to the surface. The failure of this dual barrier (cement and seal assembly) system to seal the annular space can result in serious problems that might jeopardize a well’s integrity. Typically, in field applications, the length of a casing–Liner overlap is chosen arbitrarily. In some cases, shorter overlaps (50 to 200 ft) are chosen because of the lower cost and easy identification of leaks during pressure tests. However, some loss of well control incidents (particularly the incident that motivated this study) have been linked to fluid leakages along the casing–Liner overlap. This paper investigates the critical length of the casing–Liner overlap by modeling gas leakage through the cement placed within the overlap using analytical and experimental approaches. Leakage scenarios were developed to mimic gas migration within the cement in the casing–Liner overlap. The results showed that the longer the casing–Liner overlap, the higher the leakage time. The results also showed that the current casing pressure test duration of 30 min may not be adequate to verify the integrity of the cement within the overlap. Based on the results and analyses, it is recommended to increase the pressure test duration to 90 min. In addition, the results suggest that the length of the casing–Liner overlap should not be less than 300 ft to maintain the integrity of the well in the case of gas influx. Further details are highlighted in the results section. In practice, the current rationale behind the selection of a casing–Liner overlap length is not sustainable. Thus, the major advantage of this study is that with field data, it provides both scientific and research-based evidence that can be used to inform the decision behind the selection of the casing–Liner overlap length, especially in gas migration-prone zones.
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Experimental investigation of well integrity: Annular gas migration in cement column
Journal of Petroleum Science and Engineering, 2019Co-Authors: Mustafa Al Ramadan, George Kwatia, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Abstract Cementing operations present various difficulties attributed to shallow flows all around the world. Cement ability to seal the annular space, aids in sustaining the well integrity by mitigating and preventing fluid migration to other formations and to surface. Failure of cement to seal the annular space can result in serious problems that might jeopardize the well integrity. In this study, a wellbore model setup was designed and fabricated to mimic the gas migration in cemented annulus. A series of experiments were conducted on this setup to examine the cement sealability of neat Class H and neat Class G cements, and to also evaluate the effect of anti-gas migration additive on the cement sealability. Different additives were used such as bentonite and latex. Experiments conducted revealed that neat Class H, Class G, and any other slurry design with additives (but without anti-gas migration additives) does not have the ability to serve in mitigating gas migration. The wellbore permeability of annular cement using neat Class H and Class G cement was ranging between 10−3 to 10−1 mD. In addition, it has been found that the wellbore permeability of annular cement increases as cement age increases. Annular cement should not be considered as the primary barrier when Liner-Hanger is used.
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evaluation of Liner Hanger seal assembly and cement sheath as a dual barrier system implications for industry standards
Journal of Petroleum Science and Engineering, 2019Co-Authors: Shawgi Ahmed, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Abstract Liner Hanger seal assembly and cement sheath are essential barrier elements for well drilling and completions. During installation, the Liner Hanger seal assembly is set up-stream to the cement column. This arrangement prevents the evaluation of both the Liner Hanger seal assembly and cement sheath independently. Currently, there are no testing procedures, industry standards, or regulatory guidelines for testing this type of dual barrier system independently. The primary objective of this study is to establish that cement sheath can act as a secondary barrier element in a dual barrier (elastomer seal and cement sheath) zonal isolation system, if the elastomer seal (primary barrier) is faulty. In the context of this study, the term "barrier" describes the use of cement sheath and elastomer sealing element in a Liner Hanger to prevent uncontrolled migration of formation fluid to a shallow formation or surface facilities. Another objective is to evaluate the effect of using an anti-gas migration additive on cement sealability. To achieve these objectives, experimental testing procedures were developed to evaluate the performance of a Liner Hanger seal assembly and cement sheath. Two experimental scenarios were considered in this study. The first scenario included testing faulty ethylene propylene diene monomer (EPDM) elastomer with neat Class H cement and the second scenario included testing faulty EPDM elastomer and Class H cement mixed with a commercial gas migration control additive. The tests were conducted at different pressures and wait on cement (WOC) intervals. The results revealed that neat Class H cement cannot act as a secondary barrier and prevent gas migration in the case that the primary barrier (elastomeric element of the Liner Hanger) is faulty. The cement slurry with the commercial gas migration control additive can act as a secondary barrier in case the primary barrier is faulty. The results also showed that WOC time improves cement sheath sealability. In addition, pipe material and surface roughness play key roles in the cement slurry bonding process. The major addition to the literature from this study is that for cement sheath to be considered a secondary barrier element in a dual barrier zonal isolation system, it must contain a specific anti-gas migration additive in addition to other cement additives. This specification should be included as a standard regulatory practice and should be adopted for every well section.
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Experimental investigation of elastomers in downhole seal elements: Implications for safety
Polymer Testing, 2019Co-Authors: Shawgi Ahmed, Chinedum Peter Ezeakacha, Saeed Salehi, Catalin TeodoriuAbstract:Abstract One of the multiple barriers that is installed in the downhole during drilling and completion is the Liner Hanger seal assembly. The Liner Hanger is used to engage the Liner, connect it to the previous casing, and seal off with cement before a pressure test is performed. Verifying the sealability of the elastomeric element in a Liner Hanger is a critical factor for well integrity. In this study, the performance verification process and tests were conducted based on critical reviews of literature, current regulations, and applicable industry standards. The objectives of this experimental study are to develop testing protocols to investigate the performance of common elastomeric seals that are used in a Liner Hanger seal assembly. Ethylene propylene diene monomer (EPDM) and nitrile butadiene rubber (NBR) were selected for the tests because they are commonly used in downhole sealing systems. The results from the experiments revealed that the elastomeric seals did not exhibit any leakage when they were subjected to a pressure test of 40 psig (275.79 kPa) under normal conditions. The sealing performance of EPDM and NBR after surfactant degradation was not impaired for the test conditions used in this study. However, both elastomers failed the pressure tests and leaked when a mechanical defect was intentionally created and after exposure to carbon dioxide. The pressure cycling results showed that elastomers energization plays a critical role in maintaining their seal integrity. The results also showed that prolonging the pressure test duration from 30 to 60 min did not affect the elastomers performance.