CASE HISTORY- FERROUT 100 - HDC XREAM

Ninian Central Well: - Injector

This well was drilled and put on line as a seawater injector with an initial injection rate of 10,000 bwpd. This injectivity declined over the years between 2000 to 4000 per day. The decline was the result of long-term bacterial activity causing sulphide scale and/or possible barium scale within the tubing, and heavy accumulations around the formation.

After analysis of the solids, a treatment of HDC XREAM based - Ferrout 100 series sulphide/sulphate dissolver was selected for injection. ( injection temperature 35°C, 25,000' depth)

Seventy-nine barrels of Ferrout were injected into the well. An immediate drop in back pressure was noted as the chemical reached the formation, indicating a rapid dissolution of solids. The well was shut in with the chemical soak for 24 hours and then allowed to flow back. Analysis of the sampled returns indicated an average between 550 to 650 kilograms of dissolved sulphide/sulphate scale within the solution. (Flow back analysis performed by OCT on behalf of CNR).

After flow back, a drift tool was run prior to setting a deep injection valve. This operation was notable in that it was performed without difficulty. Previous attempts had resulted in sticking of drift tools and packers.

Samples of scale retrieved from the drift tool indicated the scale was very friable, meaning the HDC and Ferrout were still reacting at the low temperature end of the upper tubing surfaces.

The well will be brought back on stream as an injector when the impact on other production issues are resolved.

The Ninian Central well has been regarded as a very successful operation. The weight of scale dissolved was significantly higher than would be expected under the temperature regime used and the relatively low volume of chemical deployed for the length of the target area covered.