Technology Update: Modeling Advances ER Openhole Horizontal Gravel Packing

Abstract

Advances in drilling technology are producing record-breaking extended-reach (ER) wells. The record for displacement from a floating installation has been pushed beyond 24,500 ft, and horizontal completions longer than 6,500 ft have become commonplace. Well-completion technology is also evolving. To facilitate cost-effective well-construction programs, completions engineers are increasingly exploring materials science and incorporating computational/numerical-modeling techniques to anticipate induced material deformations from ER processes. Sand-Screen Deployment Many ER wells are openhole completions requiring sand management to guarantee trouble-free, interventionless production. Therefore, it is necessary to address the problem of sand-screen deployment and gravel placement. In considering screen deployment, drag force on the screen must be analyzed. Greater well displacements imply higher total drag force. This force may become larger than the downward force available from the string weight, preventing the sand screen from reaching the required depth. Drag may also physically damage the sand screen. Reducing the drag force requires stronger, lighter screens and low-drag fluids. Counteracting the drag forces exerted on openhole wells requires stronger, lighter screens and low-drag fluids. Meanwhile, circulating gravel packs are subject to the limitations of fluid frictional pressure loss during gravel placement vs. increased fluid leakoff and the fracture pressure of the exposed reservoir. Placement fluids with low hydraulic frictional pressure loss are one avenue for study. Lightweight gravels requiring lower circulating rate for placement—and hence inducing lower friction pressures—are another. Deepwater ER wells, in particular, are a significant challenge. These wells often have excessive fluid loss, variations in hole stability and hole geometry, and/or an extremely narrow window between bottomhole pressure and fracture gradient. The narrow pressure window, in particular, can be a significant concern because high pump rates required for long-distance proppant transport may fracture the formation, causing fluid loss and a sand bridge or early screenout during gravel placement. The pumping boundaries for openhole gravel packing are Qmin, the rate at which a sand bridge is likely to form (typically considered to be a dune ratio of 85%), and Qmax, the rate that would result in formation fracturing pressure. Critical rates occur in washed-out hole sections and at extreme displacements, where Qmin can exceed Qmax. Therefore, reducing Qmin is a critical element in planning a long, ER openhole gravel-packing operation. An ideal solution is to use the low settling velocities of reduced-density gravels. The issues affecting the suitability of these new materials are the main theme of this article. Conventional gravels used for sand control have been sized natural sands and manufactured ceramics. The specific gravity (sg) of these materials varies between 2.65 and 2.71. For a typical wellbore configuration with an 8½-in. open hole, the ideal placement rate would be approximately 9.5 bbl/min, generating friction pressure greater than 5,000 psi in a borehole length of 5,000 ft. This additional pressure on the formation is generally well above the fracture pressure and would result in an aborted gravel-pack attempt.