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.