Schlumberger

Performance Report: BREAKDOWN with D-SOLVER D Promote Injectivity

Challenge: A well in the UK sector of the North Sea came on stream as a Rotliegendes gas producer in September 1998. A production logging tool run indicated water ingress at the base of the perforations with a rising water interface. The proposed sidetrack aimed to enter the Rotliegendes at an angle of 90°, with a 500‐ to 2000‐ft (152‐ to 610‐m) reservoir section to increase wellbore contact with the reservoir to maximize reserves recovery. The well would be completed with a 230‐micron standalone premium screen. Formation or completion impairment would need to be avoided to maximize productivity, minimize drawdown and discourage water encroachment.

Solution: A 9.0‐lb/gal (1.08‐SG) FLOPRO NT fluid would be designed to seal the formation face and minimize filtrate invasion while delivering optimum drilling performance. 1‐2% KLA-STOP NS additive would be used to minimize low‐gravity‐solids (LGS) buildup and help maintain a pristine filter cake. The BREAKDOWN chelant/enzyme‐breaker system was chosen for its ability to fully remove the FLOPRO NT filter cake from the sandface, while controlling breakthrough time. This would ensure that the well did not take losses prior to pulling out of the hole with the washpipe and closing the Fluid Loss Control Valve (FLCV). The FLOPRO NT reservoir drilling fluid/ BREAKDOWN breaker yielded positive results in an independent return permeability study.

Result: An 8½‐in. hole was drilled with VERSACLEAN LT oil‐base mud through the Haisborough group and Zechstein sequence. The 7‐in. liner was set, and a 6‐in. hole was drilled through the Leman Sandstone reservoir with the FLOPRO NT system. A solids‐free FLOPRO NT fluid was displaced into the well prior to running screens. The 9.0‐lb/gal (1.08‐SG) BREAKDOWN breaker was spotted after the screens and packer had been run. The BREAKDOWN breaker allowed the 2⅞‐in. washpipe to be pulled from inside the screens and the FLCV to be closed without losses to the formation.
An average permeability of 2 mD was expected, but the logging‐while‐drilling (LWD) resistivity tools showed a better reservoir section in terms of porosity. As a result, permeability values were expected to increase. The well test analysis reported an average value of 10 mD. The field well test analysis revealed no skin damage.

A FLOPRO NT system was used to drill the 8 ½ in. hole in the reservoir section to TD for this injector well. At TD a trip was made out of the hole and then a clean out assembly along with M-I SWACO Specialized Tools was tripped in. A FLOPRO SF pill was spotted in the 8 ½ in. open hole and approximately 265 ft inside the existing 9 ⅝ in. casing. An open hole displacement train consisting of a high viscosity transition pill, a wash pill, followed by a high viscosity tail was used during the displacement process. The pipe was then pulled to 9 ⅝ in. casing shoe and the FLOPRO NT in the casing was displaced out first to seawater and then to 9.1 ppg sodium chloride brine with 2% KCL.

The sand screen and the completion assembly were run and the FLOPRO SF in the open hole and above the packer as displaced out to brine. The pipe was pickled with a combination of SAFE-T-PICKLE and acid. The well was then gravel packed without any losses.

After the gravel pack the BREAKDOWN with the D-SOLVER D was spotted in the open hole between the sand screen and the formation (through the gravel). The wash pipe was pull and the fluid loss control valve closed.

Injection commenced after the well was completed.

Mixing Procedure: The BREAKDOWN with D-SOLVER D was mixed in a separate and clean rig pit. After filling the pit with water all the ingredients were mixed until the desired pH target was reached. The WELLZYME A was the last component added to the BREAKDOWN D-Solver D system. It was added on top of the pit 1-2 hours prior pumping to the well.


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