Schlumberger

Performance Report: CLEANPERF WB System Helps Boost Production Two-Fold in Libya

Challenge: An operator in Libya required a water-based fluid loss control mechanism that could be dispersed easily without requiring acids, breakers or other post-job remedial treatments. Further, the solution would have to provide thermal stability for more than 10 days at 285 °F (141 °C) BHT. Prior to beginning production, the fluid also must support a high static overbalance of 1,650 psi in the wellbore during perforating and completion operations.

Solution: M-I SWACO recommended the operator employ a customized CLEANPERF WB system designed to create a thin and impermeable filter cake that would remain intact under downhole conditions, thus preventing losses and limiting the invasion of solids and fluids inside the perforation tunnel immediately after perforating. The DeepClean chemistry was suggested as the best chemical at the prevention of emulsions between the filtrate and crude oil. Enhanced flowback capabilities also were incorporated in the CleanPerf WB system by utilizing organophilic components to eliminate the need for a post-job chemical cleanup treatment. Potassium formate brine was selected as the base fluid to provide the required density while also enhancing the thermal stability of the fluid and inhibiting any reactive interstitial clays in the reservoir. Multiple fluid compatibility tests were conducted between the crude oil, formation water and the CleanPerf WB filtrate to evaluate the ability of various emulsion preventers to eliminate potential emulsions.

Result: Once the CLEANPERF WB system was spotted across the 5-in. liner prior to perforating, losses in the range of 1.6 bbl were expected. While only 0.6 bbl was actually lost within the first two hours of the perforating operation. Losses dropped to zero for the remainder of the job.The CleanPerf WB fluid remained stable while running the upper completion over the next 11 days, after which the well flowed back without the need of a chemical treatment. The production from the well was two times higher than expected. The reservoir exhibited low skin values with the operator judging the CleanPerf WB application as a success, and clearing the way for its use in future operations.

The CleanPerf WB system was designed with a density of 9.1 lb/gal (1.09 sg) to provide the desired 1,650 psi overbalance in the 5-in. liner. Geologists at the M-I SWACO headquarters in Houston conducted thin-section analyses of core material provided by the operator. The formation was identified as quartz sandstone (quartz > 95%) with minor clays and carbonate minerals. From these analyses, pore sizes and interconnectivity of the pores were determined. Based on the maximum pore size revealed in the test, M-I SWACO proprietary OPTIBRIDGE software was used to develop the optimum blend of bridging agents to effectively seal the full range of pores present in the formation. Further, Return Permeability Tests were conducted on the cores with the CleanPerf WB system showing no damage to the reservoir under bottom hole conditions.

Fluid compatibility tests between the crude oil, formation water and the CleanPerf WB filtrate were conducted in the M-I SWACO lab in Dubai. These tests revealed a tendency for precipitation when the CleanPerf WB filtrate was mixed with the formation water and an unbreakable emulsion was formed when the filtrate was mixed with the crude oil. One of the chemicals in the CleanPerf WB formulation, which was found to be the cause of the precipitation, was subsequently removed. Several emulsion preventers and breakers were added to the fluid and DeepClean chemistry was found to be the best chemical for preventing emulsion formation.

The thermal stability of the CleanPerf WB was checked after aging the fluid for a period of 10 days at downhole temperature to verify the ability of the fluid to maintain rheological and fluid loss control properties for the duration of completion operations.

Operationally, the CleanPerf WB system was mixed at M-I SWACO Libya facility and sent to location as a finished system. A total of 30 bbl of fluid was sufficient to cove directly from the transport truck to the coiled tubing unit, thereby eliminating the risk of losing or contaminating the fluid. The CleanPerf WB system was spotted as a balanced plug with 10 bbl used as a spacer to prevent dilution at the interface. The interval was then perforated using the PURE perforating system using a “Dynamic Underbalance” technique to increase productivity. After running the upper completion the well was brought on production without any problems.


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“The CLEANPERF WB system was used to minimize formation damage under extreme wellbore conditions, delivering low skin values and increased production.”
Willy Lopez
Wellbore Productivity Technical Services
M-I SWACO NA