Proposal Described are proof-of-concept developments to form a seal for mitigating sustained casing pressure caused by annular pressure buildup. Annular pressure can result from numerous sources, including tubing leaks, loss of isolation potential within the cement column because of poor mud displacement, free water-induced channels, stress fractures, and failure of the cement to cover all potential sources of annular pressure. In most cases, annular pressure is not observed at the wellhead until the well is placed on production, making it difficult to identify, access, or remediate the pressure source. A new and novel approach to remediation has been tested in which a low-melt-point alloy metal is dropped down the backside of the casing where annular pressure has been observed. The metal is allowed to accumulate at the top of cement or other physical barrier, melted with an induction-heating tool, and allowed to cool and solidify. This process forms an annular seal to stop fluid communication between the formation and wellhead. This method was demonstrated within a full-scale, simulated well section. An electromagnetic induction tool provided sufficient localized heating to completely melt solder-type alloy metal placed between concentric casings. Subsequent pressure-testing verified that a complete melt, sufficient to provide an effective seal against fluid pressure, was achieved in both water- and synthetic-based drilling fluids. Shear-bond test results of various alloys were equal or superior to cement, and the solid-liquid phase transitions (set points) occurred at precise temperature levels. All metals tested contained bismuth because of its unique characteristic of expanding upon solidification to provide enhanced pressure-containment performance. Full-scale testing was conducted using 17-ft long concentric annular models constructed of 8-in. and 5-in. diameter steel pipes. Subsequent field-testing is currently being planned.

Abstract This paper shows the benefits of modeling a horizontal gravel-pack interval before attempting to install the gravel pack. Gravel-packing techniques for long horizontal well sections were evaluated with a laboratory model of a casing/borehole annulus. In the horizontal section modeled, permeability is sufficient to interfere with the transportation and distribution of pack sand from total depth to dogleg when positive differential pressure is maintained. The goal of this modeling experiment was to predict whether the formation's permeability at the sandface could be reduced enough to allow successful gravel packing without damaging the formation far beyond the sandface. Gravel-packing technology is well established for near-vertical wells, with off-the-shelf equipment and textbook procedures readily available. The exceptionally long producing intervals in horizontal wells present a greater challenge for gravel packing, however. Interval permeability is, by design, continuous. This continuous permeability both enhances well productivity and allows increased wellbore fluid flow into reservoir rock. When the permeable formation absorbs the fluid energy necessary to evenly disperse pack sand throughout the section, sand bridging can result, restricting the flow before the pack sand is fully distributed across the entire interval. The laboratory model simulates the axial flow of drilling and/or completion fluids through an annulus. The model has an impermeable confining wall (simulating the casing) and a permeable wall (simulating reservoir rock). Recently, it was used for testing the capacity of a drill-in fluid to reduce reservoir near-face permeability, and allow sand propagation throughout a long horizontal interval. Results obtained both in the laboratory and in subsequent field trials validate the use of a drill-in fluid in reducing near-sandface permeability. The procedure has been used successfully on multiple horizontal wells with typical horizontal section lengths of 1,000 to 2,500 ft. Plans are underway to continue the practice in additional wells.

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.

Abstract In some Middle Eastern wells, the serious problem of shallow casing leaks results from an insufficient cement seal across a corrosive water formation containing hydrogen sulfide (H2S). Factors contributing to this poor seal include multiple weak adjacent zones and thin lenticular washouts, which complicate conventional cementing practices by preventing slurries from sealing off water-bearing formations and protecting the well casings. Historically, multistage cementing has only marginally improved zonal isolation in this region. High-quality foamed slurries [slurries with high volumetric concentrations of nitrogen (N2)] can enable coverage of the weak zone, but these slurries are too permeable to provide long-term casing protection. A joint study conducted to address casing-leak problems in a Middle Eastern field has yielded custom cement blends that mitigate the combined detrimental effects of (1) water containing H2S, (2) mud or whole-cement losses to lost-circulation zones (zones with very low fracture gradients), and (3) muddisplacement deficiencies primarily caused by multiple washed out sections. Successful slurries that appear (based on laboratory results) to combat these problems are foamed with nitrogen and feature a combination of Portland and pozzolan cements plus hollow pozzolan spheres. This paper discusses large-scale tests and the blends designed for these tests. Researchers conducted these tests in an attempt to prove the effectiveness of certain cement blends and to help optimize those blends. The tests show that foamed, lightweight (8 to 10 lbm/gal) slurries containing hollow pozzolan spheres with pozzolan cement can enhance the sealing of harsh-water zones. This enhancement is achieved by the combined effects of two events: (1) improving displacement of drilling mud and cuttings by optimizing foam quality, and (2) cementing past lost-circulation zones. Details of blends, test setups, and test results are discussed.