Gravel Packing Wells Drilled With Oil-Based Fluids: A Critical Review of Current Practices and Recommendations for Future Applications

Abstract

Abstract Many of the recently discovered reservoirs in deepwater/ subsea environments are prime candidates for horizontal open-hole gravel packs. Presence of multiple reactive shale breaks and penetration of different sand bodies along these holes introduce a formidable challenge for selection of proper carrier fluids, considering that most of these wells require oil-based (OB) drilling fluids. Various procedures were practiced for gravel-packing wells drilled with OB fluids, most utilizing water-based (WB) carrier fluids. Primary concern in using WB carrier fluids is the destabilization of the shales. If the displacements to WB fluids are performed prior to running in hole with the sandface completion assembly, inability to run the screen assembly to target zone is the risk. Consequently, operators were forced to use a two-step process, whereby a predrilled liner is run in hole in OB fluid environment, followed by displacements to WB fluids and gravel-packing with WB fluids. This approach introduces additional rig time and increases completion costs. If the displacements to WB fluids are performed after running in hole with completion assembly, primary challenge is the prevention of screen plugging. This necessitates a comparison of the benefits and risks of displacements to solids-free oil-based fluids and conditioning of the OB drilling fluid, considering logistics. An additional consideration in gravel packing with WB fluids in reactive-shale environments is the risk of intermixing of gravel with shales, thus reduced gravel-pack permeability. Various approaches may be taken to minimize this risk. The type of carrier fluid must also be kept in mind from a formation and gravel pack damage standpoints, should losses be experienced during gravel packing. Another approach in reactive shale environments is to use an oil-based carrier fluid and avoid exposure of the open hole to WB fluids both prior to and during gravel packing. This approach, practiced in two applications, also has its limitations. In this paper, a critical review of gravel-packing practices in oil-based drilling environments is provided, along with some of the recent developments and recommendations for future applications based on lessons learned from earlier practices. Introduction A significant proportion of global oil and gas production comes from formations that are prone to sand production during well life. Increasingly, reserves are being discovered and brought into production in such formations in deep water where the high facilities, sub-sea, well construction and intervention costs mean the planned reserves recovery per well are often very high, as is the expected well productivity to maximize the production rate. Both require effective sand control for the life of the well, often including the impact of high water cuts or depletion, as well as minimizing pressures losses across the completion and in the tubing. In addition, in several parts of the world high rate gas wells are being completed in unconsolidated formations where eliminating sand production and rate dependent pressure losses are critical well objectives.