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This paper documents a novel engineering approach and the operational methodology used to achieve high efficiency remediation on two offshore applications. Results are presented, detailing specific placement procedures, in-situ treatment design and productivity improvements.
Two wells were recently drilled and completed for the Rosa deepwater project, Block 17 offshore Angola, using a Non-Aromatic Oil-Based Mud (NAOBM) weighted with sized calcium carbonate. After installing the Stand-Alone-Screens (SAS) across the production intervals and allowing the wells to cleanup, the Productivity Index (PI) measured on each well was very disappointing. A diagnosis study concluded that the severe productivity impairment on these wells was related to either screen plugging by mud particles while running the screens to bottom in the NAOBM and/or the plugging induced by a mixture of formation sand, mud, and filter cake when draw-down was applied during cleanups.
Based on collaborative laboratory work between the operator and a service company to design a treatment fluid for removing NAOBM filter cake material for water injection wells, a microemulsion spotting fluid was formulated to remediate the damage in the two Rosa wells. The formulation contains a surfactants blend, acetic acid, and brine. The remediation was performed using a Coiled Tubing (CT) equipped with a rotating jet blaster to spot the treatment fluid inside the screen assemblies. Each treatment was allowed to soak. After the placement of the treatment pills on each well, cleanup measurements indicated significant PI improvements close to expected values. Production Logging Tests (PLT) analysis indicates that both wells are producing from almost all screen lengths.
Despite the challenging placement of the treatment fluid in the SAS assembly, the diffusion of the microemulsion with acid allowed break up and removal of blocking solids from the completion screens and filter cake residues from the wellbore walls, allowing full production.