Wells treated with the reservoir remediation system showed sharp improvements in production. (Graph courtesy of Baker Hughes Drilling Fluids)

A major operator in the deepwater area of Angola recently drilled two wells and installed stand-alone sand exclusion screens for openhole completions. The two wells were drilled with a non-aromatic oil-based mud (NAOBM) weighted with sized calcium carbonate. After conditioning the OBM at total depth, the fluid was circulated and screened across the shale shakers to remove the larger mud solids and minimize plugging of the screens during production.

After installing the stand-alone screens across the production intervals and allowing the wells to cleanup, the productivity index (PI) measured on each well was very disappointing. Upon having carefully reviewed both well histories and carried out various laboratory tests, it appeared that the severe productivity impairment observed on each of the wells was mainly related to screens plugging by a mixture of mud solids, filter cake, shale particles and formation sand.

From logs interpretation, total reservoir net vertical lengths were 253 ft (77 m) on the first well (Well-1) and 197 ft (60 m) on the second (Well-2). Both wells were deviated (respectively 48° and 53° in the reservoir). The PI on Well-1 was 3 with a maximum achievable production of 700 b/d of oil. Well-2 produced a meagre 180 b/d of oil and had a measured PI of just 0.5. The combined expected production from these two wells was initially estimated at greater than 25,000 b/d.

The operator had already made a significant investment in drilling when the decision was made to turn to Baker Hughes Drilling Fluids for a solution. The MICRO-WASH high-definition reservoir remediation system was applied across the inside of the completion screens in each well with a coil tubing unit equipped with a rotating jet blaster tool. The densities of the reservoir remediation system were 9.5 lb/gal and contained 10% acetic acid. Two openhole volumes of the reservoir remediation system were applied across the damage zone in each of the wells and allowed to soak for about 16 hours.

MICRO-WASH is formulated to put both organic and inorganic solid particles into solution, leaving screened completions free from impairment. Oil based drill-in fluids also form an internal filter cake in the near wellbore area and this invasion of oil filtrate and deposition of fine solids alters the wetability and effective permeability of the reservoir. The reservoir remediation system works quickly to reverse this damage to improve production or injection.

A production logging tool (PLT) log was run at the end of a 24-hr flow-back period. Analysis of the logs indicated that in both wells, crude oil was flowing through 100% of the completion screens in contact with a producing sand section. The reservoir remediation system was able to transform these severely damaged reservoirs into viable production assets, increasing production by more than 24,000 b/d of oil, delivering significant economic value to the operator. The reservoir remediation system was able to reduce the skin damage in each well from 660 and 800 to 15 and 16, respectively.

The production index for each well increased from nearly zero to 75 and 130 respectively. On Well-1, the production volume increased from 700 b/d of oil to more than 9,000 b/d. An even greater increase was seen in Well-2, which went from 160 b/d to more than 16,000 b/d of oil. The incremental value to the operator after the reservoir remediation system was used was US $1.7 million per day. Based on final production figures, the reservoir remediation system treatment was paid for in less than six hours by the increase in production from the two wells.

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