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The wellbore displacement is a necessary and critical step toward subsequent completion operations and production. A successful displacement process saves significant rig time, cuts disposal volume, reduces fluid contaminations and provides the best opportunity for a successful completion. Traditionally, a displacement train typically has multiple cleaning spacers, including a solvent spacer and a surfactant spacer. It is highly preferred to have a cleaning spacer to achieve the desired wellbore cleanliness as a single stage and with minimum circulation volume. Surfactants, solvents and emulsions are used in the cleaning spacer(s) for displacement of invert emulsion drilling fluids (IEF). The spacer system is selected depending on the displacement requirements and wellbore conditions. This paper describes innovative double–emulsion technology that shows highly efficient and effective performance in IEF displacement, as the design fully combines the power of both surfactants and solvents. This paper presents theoretical and lab testing results for fundamental understanding of IEF film removal from metal surfaces under various conditions. It was found that the solvency and surfactancy play different roles during the film removal process. A macroemulsion or microemulsion contains both solvents and surfactants but they often have a limited operational window with reduced solvency and surfactancy. Based on the analysis described in this paper, an innovative double-emulsion system was developed to fully preserve the solvent cleaning power and dispersive and water–wetting power of surfactants. It has a unique water-in-oil-in-water structure, in which the dispersed solvent droplets contain smaller droplets of a second aqueous phase. The solvent droplets effectively remove the top layer of mud film and directly deliver the surfactants to the metal surface. This technology has been applied in various successful field applications.
The wellbore displacement is a necessary and critical step toward subsequent completion operations and production. A successful displacement process saves significant rig time, cuts disposal volume, reduces fluid contaminations and provides the best opportunity for a successful completion. Traditionally, a displacement train typically has multiple cleaning spacers, including a solvent spacer and a surfactant spacer. It is highly preferred to have a cleaning spacer to achieve the desired wellbore cleanliness as a single stage and with minimum circulation volume. Surfactants, solvents and emulsions are used in the cleaning spacer(s) for displacement of invert emulsion drilling fluids (IEF). The spacer system is selected depending on the displacement requirements and wellbore conditions. This paper describes innovative double–emulsion technology that shows highly efficient and effective performance in IEF displacement, as the design fully combines the power of both surfactants and solvents. This paper presents theoretical and lab testing results for fundamental understanding of IEF film removal from metal surfaces under various conditions. It was found that the solvency and surfactancy play different roles during the film removal process. A macroemulsion or microemulsion contains both solvents and surfactants but they often have a limited operational window with reduced solvency and surfactancy. Based on the analysis described in this paper, an innovative double-emulsion system was developed to fully preserve the solvent cleaning power and dispersive and water–wetting power of surfactants. It has a unique water-in-oil-in-water structure, in which the dispersed solvent droplets contain smaller droplets of a second aqueous phase. The solvent droplets effectively remove the top layer of mud film and directly deliver the surfactants to the metal surface. This technology has been applied in various successful field applications.
Reactive mud cake breaker fluids in long open hole horizontal wells located across high permeability sandstone reservoirs has had limited success because they often induce massive fluid losses. The fluid losses are controlled with special pills, polymers and brine or water, causing well impairment that is difficult to remove when oil-based mud (OBM) drill-in fluids (DIFs) are used. This situation has resulted in the drive for an alternative cleanup fluid system that is focused on preventing excessive fluid leak off, maximizing the OBM displacement efficiency and allowing partial dispersion of the mud cake for ease of its removal during initial well production. The two-stage spacer application is composed of a nonreactive fluid system, which includes a viscous pill with nonionic surfactants, gel pill, completion brine and a solvent.Extensive laboratory evaluation was conducted at simulated reservoir conditions to evaluate the effectiveness of the OBM displacement fluid system. The study included dynamic high-pressure/high temperature (HP/HT) filter press tests and coreflood tests in addition to wettability alteration, interfacial tension and fluid compatibility tests.The spacer fluid parameters were optimized based on wellbore fluid hydraulic simulation and laboratory test results, which indicated minimal fluid leak off and a low risk of emulsion formation damage. Three well trials were conducted in a major offshore field sandstone reservoir drilled with OBM. All three trial wells (one single and two dual laterals), which were treated, have demonstrated improvement in production performance. This paper will discuss in detail the spacer fluids optimization process, laboratory work conducted and the successful field treatments performed.
Angola is home to two of BP's largest subsea developments, Greater Plutonio and PSVM. High rate production wells have been achieved through the use of long open hole gravel pack completions, with alternate path screen design. Since the screens are deployed in conditioned oil based mud, the open hole is displaced to aqueous fluid prior to gravel packing the well. The early Greater Plutonio wells extensively utilised what is referred to as the 'conventional,' 'forward,' or Heel-to-Toe technique to displace the oil based fluid to water based. However, depletion of some of the reservoir sands increased the likelihood of screen plugging in wells with long open hole sections, as demonstrated by a handful of incidents. Also, the tight pore pressure to fracture gradient (PPFG) windows and small screen gauge sizes in the PSVM development made the 'forward' technique less suitable to adopt as a basis of design. As such, both projects developed a different displacement technique referred to as 'reverse' or Toe-to-Heel circulation to overcome the issues of sand control screen plugging and small PPFG windows. Work was performed to confirm that service tools could maintain full functionality, the fluid pill train properties were appropriate, and that hydraulic models could adequately predict the ECDs generated during the displacement. Eight open hole gravel pack wells, across both projects, have now been successfully completed using the Toe-to-Heel technique. Using the data from these wells, along with the existing data set from the earlier Greater Plutonio wells, it has been possible to determine a set of guidelines which indicate which technique is best suited under certain conditions. This paper briefly describes the history of the two projects, details the operational differences between both methods, describes the evolution of the modelling work done for ECD prediction, including several pros and cons associated with each method. The actual displacement data is also presented, and is compared with the predictions from the initial modelling simulations. The development of even more accurate modelling techniques is also discussed.
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