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.