For offshore wells requiring sand control, the trend in the industry has been to gravel pack longer and longer wells to access more reserves with reduced well count. In challenging environments (e.g., low frac pressure), gravel packing with shunt tube technique is the preferred option. This paper discusses development and qualification of an enhanced shunted alternate path technology (ESAPT) screen that will extend openhole gravel packing lengths to more than 7,000 ft with zonal isolation. Extending openhole gravel pack lengths with shunt tubes required several issues to be addressed. First, if static shunting (bypassing an annular blockage through shunts and packing in a toe-to-heel fashion downstream of the blockage) occurs intentionally or unintentionally, large volumes of slurry will exit through a limited number of shunt tubes manifolds before complete packing, raising erosion concerns which were addressed through: 1) computational fluid dynamics simulations to identify the location of maximum erosion and to redesign the shunts geometry and metallurgy accordingly; 2) yard tests with slurries passing through the manifold at rates representative of field applications. Second, if continuous shunting (bypassing an annular blockage through shunts and packing in a heel-to-toe fashion downstream of the blockage) occurs, the pressure inside the shunt tubes can: 1) exceed the burst pressure limit of conventional shunted alternate path technology (CSAPT) screens, which was addressed through modification of the weak links in the CSAPT and then tested to the required burst limit; 2) cause higher fluid leak-off through the packed interval, resulting in increased gravel concentration, increased friction and potential bridging inside the shunt tubes, which was addressed through a) leak-off behavior characterization of carrier fluids in shunt tubes of packed interval; b) friction pressure measurements with various gravel concentrations and rates inside shunt; c) modification of nozzle distance based on results from (a) and (b), and d) verification of the modified design through gravel pack yard testing. Recent testing demonstrated that under static shunting conditions, CSAPT shunt system can have substantial erosion in long interval gravel packing. ESAPT shunt system showed significantly improved erosion resistance for slurry flow in yard tests. It was demonstrated that ESAPT shunt system could withstand 10,000 psi burst pressure after flowing 450 klbs of proppant at 5 bpm slurry rate. It was also successfully tested for 10,000 psi burst pressure at elevated downhole temperature of 300F. The data from leak-off tests of viscous fluids through packed interval shunt tubes at high differential pressures combined with friction pressure measurements with various gravel concentrations and rates (gravel concentrations as high as 20 ppa and rates as low as 0.25 bpm) led to the conclusion that the distance from the shunt manifold to the first nozzle needed to be increased for longer wells to be gravel packed. In a yard test using a full-scale model of the new design with the increased nozzle distance, and including the blank handling sections, a complete pack was achieved with proppant. An ESAPT screen that will push the openhole gravel pack lengths to more than 7,000 ft with zonal isolation is presented herein. The system has a more erosion-resistant, high burst pressure shunt system and allows quicker make-up of screen joints on the rig floor.
Summary For offshore wells requiring sand control, it is beneficial to extend the openhole length to access more reserves with a reduced well count. In challenging environments (e.g., low fracture pressure, highly unconsolidated sand), gravel packing with shunt tubes has been used successfully to virtually ensure a complete pack, thereby minimizing the risk of sand-control failure. Although shunt-tubegravel-pack technologies already exist, several issues must be addressed to gravel pack longer wells. First, the extra volume of gravel passing through shunt-tube manifolds raises erosion concerns. Second, the burst rating of the entire shunt system needs to be increased to allow continuous packing through shunts in a heel-to-toe fashion. Third, higher leakoff through the packed interval might increase gravel concentration, which increases friction and the risk of bridging inside the shunts. This study discusses the development and testing of a modified shunted screen that could extend openhole gravel-packing lengths to more than 7,000 ft with zonal isolation. The first step was to use computational fluid dynamics (CFD) simulations to investigate the erosion-prone areas in our existing conventional shunted-screen-technology (SST) manifold design. The CFD results were then used to modify the manifold and make it more resistant to erosion. Prototypes were manufactured and erosion tests were conducted to validate and qualify the new design for targeted proppant concentrations, flow rates, and treatment volumes. Any weak areas found in the shunt system were modified to enable higher burst pressure. The modified shunt system was then independently tested to quantify the burst limits. The concerns regarding high leakoff, friction, and bridging inside the tubes were first addressed by means of experimentation. The first nozzle distance was then modified according to these results. Verification of the modified system design was performed by means of gravel-pack testing on a full-scale model. It was observed that the proposed enhanced-SST (ESST) had no erosion failure after 450,000 lbm of proppant at a slurry rate of 5 bbl/min. The proposed ESST was successfully tested for 10,000-psi burst pressure after the erosion test. The initial motivation, design changes, and tests that led to the development of the modified system are presented herein.
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