Drill-In Fluid Filter-Cake Behavior During the Gravel-Packing of Horizontal Intervals — A Laboratory Simulation

Abstract

Abstract A simulated horizontal well section allows studies regarding the buildup and removal of drilling-fluid filter cake. For the study described in this paper, researchers used the well section to examine the effects and behavior of drill-in fluids before, during, and after gravel packing. Specifically, the following conditions were examined: (1) filter-cake thickness, (2) filter-cake permeability, (3) local permeability variations behind the sand face, and (4) the effects of sand scouring on the preceeding three quantities during gravel packing. The 6-ft long test apparatus resembles a linear section of casing-and-borehole annular space where differential pressure can cause drilling-fluid filter cake to develop. Temperatures in the apparatus can be increased, as needed, up to approximately 200°F, and fluid is flowed axially through the rectangular flow channel. The special design of one channel wall, which consists of permeable, unconsolidated sand, supported by screen, allows filter cake to build up. The fluid is flowed through the channel until the cake-building pressure is balanced by the flow's erosive forces. The drill-in fluid temporarily plugs the sandstone face, allowing the axial flow to carry the gravel-packing sand throughout the length of the horizontal section. Laboratory tests with this apparatus showed that a properly selected drill-in fluid can plug a high-permeability sand within seconds after contact, and reduce permeability a 1,000-fold. This low permeability can be maintained throughout the sand-pumping process, even when the filter cake is almost completely eroded. To date, this plugging procedure has been used successfully on multiple horizontal wells with a typical horizontal-section length of 1,000 to 2,500 ft, and plans are underway for it to be used on more wells. Laboratory test results closely agree with the results observed in these field wells.