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Downhole separation of gas and solids for sucker rod pumping (SRP) and electrical submersible pumping (ESP) continues to be a significant challenge, particularly for horizontal wells. A major advancement in downhole separation has been achieved by realizing there was an opportunity to intentionally take advantage of transient multiphase flow conditions where liquids phase reversals or fallback exists. Multiple case studies demonstrate that designing of a downhole separator that takes advantage of liquid phase flow reversals can enhance downhole separation performance and capacity, while at the same time lower operational risk. Improving downhole separation without undesirably increasing operational risk and cost has been challenging. A separator design that requires a packer or annular seal, such as a cup, is inherently more operationally risky from an installation and retrieval perspective. Further, a separator design that imparts pressure drops or increases flow turbulence faces the reliability risks of scale deposition and erosion. Flow turbulence can increase the entrained gas foaming tendency in the liquid and reduce gas bubble size in the liquid, consequently lowering separation efficiency and increasing pump gas interference. It is generally understood that separation capacity, in terms of gravity separation principles, has been physically limited by a separator's cross-sectional area for separation. It is less understood that separation capacity has also been limited by the location and orientation of a separator's intake, as well as the shape of the conduit in a separator's separation region, and that it has been limited by a common mechanical design practice of a concentric or centralized pump intake dip tube or mandrel. Technical literature, industry research and transient multiphase flow simulations have revealed, under certain conditions, that liquid phase flow reversals are not only present, but also occur at high frequencies. Such reversals or liquid fallback also occurs at much higher velocities than gas bubbles can rise, which suggested there is an opportunity to improve downhole separation. Industry research also disclosed that gas-liquid separation in an eccentric annulus is more efficient than in a concentric annulus and that separation efficiency is greater in a conduit shaped as an open tube versus an annulus. Such gains in separation efficiency are primarily due increased liquid hold-up, meaning increased liquid phase flow reversals or liquid fallback. It was hypothesized that downhole separation could be significantly improved by a separator engineered to take advantage of liquid phase flow reversals, thereby avoiding the limitations of downhole separators that are governed by gas bubble rise velocity. A separator was then designed, built, extensively flow loop tested and successfully field implemented. This paper describes the design process and results of the field implementation of an enhanced downhole separator. Flow loop testing results and comprehensive analytical transient multiphase flow simulation will be shared. A set of case studies, in multiple basins, reviews the field installations and presents the results of improved downhole separation performance and lowered operational risks, resulting in lowered operating expense and increased production.
Downhole separation of gas and solids for sucker rod pumping (SRP) and electrical submersible pumping (ESP) continues to be a significant challenge, particularly for horizontal wells. A major advancement in downhole separation has been achieved by realizing there was an opportunity to intentionally take advantage of transient multiphase flow conditions where liquids phase reversals or fallback exists. Multiple case studies demonstrate that designing of a downhole separator that takes advantage of liquid phase flow reversals can enhance downhole separation performance and capacity, while at the same time lower operational risk. Improving downhole separation without undesirably increasing operational risk and cost has been challenging. A separator design that requires a packer or annular seal, such as a cup, is inherently more operationally risky from an installation and retrieval perspective. Further, a separator design that imparts pressure drops or increases flow turbulence faces the reliability risks of scale deposition and erosion. Flow turbulence can increase the entrained gas foaming tendency in the liquid and reduce gas bubble size in the liquid, consequently lowering separation efficiency and increasing pump gas interference. It is generally understood that separation capacity, in terms of gravity separation principles, has been physically limited by a separator's cross-sectional area for separation. It is less understood that separation capacity has also been limited by the location and orientation of a separator's intake, as well as the shape of the conduit in a separator's separation region, and that it has been limited by a common mechanical design practice of a concentric or centralized pump intake dip tube or mandrel. Technical literature, industry research and transient multiphase flow simulations have revealed, under certain conditions, that liquid phase flow reversals are not only present, but also occur at high frequencies. Such reversals or liquid fallback also occurs at much higher velocities than gas bubbles can rise, which suggested there is an opportunity to improve downhole separation. Industry research also disclosed that gas-liquid separation in an eccentric annulus is more efficient than in a concentric annulus and that separation efficiency is greater in a conduit shaped as an open tube versus an annulus. Such gains in separation efficiency are primarily due increased liquid hold-up, meaning increased liquid phase flow reversals or liquid fallback. It was hypothesized that downhole separation could be significantly improved by a separator engineered to take advantage of liquid phase flow reversals, thereby avoiding the limitations of downhole separators that are governed by gas bubble rise velocity. A separator was then designed, built, extensively flow loop tested and successfully field implemented. This paper describes the design process and results of the field implementation of an enhanced downhole separator. Flow loop testing results and comprehensive analytical transient multiphase flow simulation will be shared. A set of case studies, in multiple basins, reviews the field installations and presents the results of improved downhole separation performance and lowered operational risks, resulting in lowered operating expense and increased production.
Mercury presence in produced fluid poses serious issues to gas production process due to HSSE risk, process disturbance and product quality for export. Mercury management is conducted based on type of mercury presence, for instance elemental mercury and solid mercury. For elemental mercury, adsorbent is typically being used, while solid mercury removal is managed via filtration. However, established mercury removal strategy is limited to "single" phase (gas, hydrocarbon liquid, water) thus can only be carried out post phase separation, while there is no available mercury removal technology for full well stream (FWS) treatment as early as at the wellhead. A novel compact separation concept based on integrated cyclone and filtration design for removing solid mercury in gas dominant full well stream was developed, to allow for flexibility in implementation location (from multiphase at wellhead to single phase post separation) and achieve reliable and consistent separation performance at 1 μm particulate size. Testing with solid mercury particles demonstrated the technology feasibility in removing particles of 1 μm and larger, where particles of 1 μm and larger was not detected by the high-speed imaging camera used at the clean fluid outlet for solid monitoring. CFD simulation conducted provided reference on the feasibility of the technology based on fluid regime and dynamics in removing solid mercury at test conditions, as well as at intended site conditions. A reliable and flexible solution is key to ensure effective contaminant management from the target production, and safeguarding production loss due to contaminant presence in the long run.
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