CASE HISTORY - HDC XREAM

North Sea : Montrose A-15

The Montrose platform has a number of severely scaled wells from the mid-1990's. Montrose A-15 was particularly problematical because the TRSCSSV valve at the mud line was scaled in a partially closed position. Calipers had demonstrated Coiled Tubing could not access the valve due to the scale volume. The scale was sampled and determined to be predominantly barium sulphate. Due to the temperature (4 ° C), de-scaling was thought unfeasible as dissolvers are traditionally, very thermally driven.

HDC XREAM was tested in the laboratory by the operator and subsequently evaluated by T.R. Oilfield Services in Aberdeen. HDC XREAM proved to be an order of magnitude more effective than the top line dissolvers on the market while not being as thermally driven.

Subsequently, a programme was initiated which entailed placement of HDC from the production deck to the seabed and the TRSCSSV. The HDC was pre-heated to 80 ° C, with a projected cooling period of 120 minutes from 80 ° to10 ° deg. C. During the placement period, a wire line brush was run up and down the area to remove the dissolving paste and expose more surface area to HDC XREAM. The total target area was from the production deck to below the mud line, or a length of ± 700'. The calculated weight of scale to be removed was approximately 600 kilograms.

To dissolve this amount of scale, the volumes had to be placed consecutively in 1800-liter lots. Each was bullheaded down the partially opened valve after cooling. During the actual operations, gel plugs to keep the fluid in place may have been lost, with the scale dissolver being over displaced. The total volume was pumped, although it is estimated 33% was lost to plug failure. All volumes ended up in the lower well. Due to plug failure, the treatment was repeated at a later date, again with 1800 liters used in sequential soak and scratch applications.

The end result was interesting in that not only did the valve free up completely, indicating that it had been simply obstructed by scale, but also this success meant the valve did not need to be retrieved. When production was restarted, the production rate had increased from 2,000 to 2,500 bpd to in excess of 3000 bpd -and increasing. (The subsequent gauge run indicated .25" ID increase in the tubing above the valve, which extrapolated to 530 kilograms of scale dissolution). The increased production alone paid for the entire chemical/mechanical operation in 5 days.

HDC had displaced (in the initial operation) through to the bottom of the well, dissolved the existing scale, and cleaned the perforations as well.

The well is currently shut in and will be re-evaluated at a later date while studies continue as to the applicability of further stimulation.