Chemical treatment to remove emulsion and polymer plugging

When production dropped from a well that was completed using an openhole slotted liner in the Bunga Raya field, the operator—Talisman Malaysia Ltd. (TML)—performed a chemical treatment to remove emulsion and polymers left by the drilling fluid used to drill the well. Immediately after treatment, production increased to 2,000 bbl/d from 500 bbl/d, but within 5 hours, it dropped dramatically and then stabilized at pretreatment rates.

TML suspected that emulsions and asphaltenes had formed in the wellbore during well shut-in while rigging down. However, TML did not have adequate information about the formation characteristics and well trajectory to understand

• the cause of the production decline after treatment
• where and how the emulsions and asphaltenes were forming
• how to completely dissolve emulsions and asphaltenes and to prevent them from reforming.

Innovative CT intervention to better understand the well

TML consulted Schlumberger to design a well cleanup, to obtain pressurized bottomhole samples, and to run a DTS. ACTive Profiling was chosen to provide a single-point temperature reading at the tool and to provide a temperature reading across the fiber optics inside the coiled tubing. The system uses fiber-optic telemetry conveyed in the coiled tubing to deliver DTS measurements.

The objectives were to

• check for conformance of the first DTS results and interpretation
• use the DTS data to select the location to collect representative bottomhole hydrocarbon samples
• optimize the treatment interval.

Innovative CT intervention to better understand the well

The pressure survey and DTS data revealed minimum pressure support from the water injector, which, in turn, caused gas cap expansion. The temperature dropped across the entire interval but was lowest at the toe. The reason for the cooling effect was gas production from the toe and heel sections caused by the gas cap expansion that limited liquid production. The combination of gas rates with oil and water production was also creating tight viscous emulsion, further hindering production performance.

TML concluded that the high gas production from the toe and heel could not be selectively shut off or controlled in the horizontal openhole slotted liner completion to perform an effective stimulation program and treat the tight viscous emulsions.