Schlumberger

Performance Report: BREAKDOWN/D-STROYER Combo Slashes Skin Values, Optimizes Production Rate

Challenge: After drilling and testing the pilot well for a gas storage project onshore Spain, the operator observed poor productivity and important formation damage, which had to be rectified before the subsequent 10-well gas storage project could begin. To achieve the desired targets of minimal skin damage and high production rates, the operator required a simultaneous solution that would combine a nondamaging reservoir drill-in fluid (RDF) with filter cake treatment. Owing to unfavorable experience on previous wells, the operator was reluctant to use mineral acid as part of a post-completion treatment, preferring instead a treatment that could be applied during the completion phase.

Solution: On the basis of the information the operator provided and taking into consideration the strict environmental restrictions on onshore drilling operations in Spain, M-I SWACO recommended the FLOPRO NT RDF for drilling the 8 ½ in. horizontal section from 3,500 m to 4,000 m (11,483-13,123 ft). To limit invasion and control losses, M-I SWACO used its OPTIBRIDGE proprietary software package to select the particle size distribution of the calcium carbonate bridging agent. The D-STROYER internal breaker was to be incorporated in the final formulation to assist in breaking down the filter cake.

Result: The performance of the BREAKDOWN/D-STROYER combination closely replicated the pre-drilling laboratory testing results. The eventual average skin value was reduced to -1, compared to a value of 8 observed on the pilot well. The use of M-I SWACO Smart RDF technology resulted in excellent productivity on this gas storage project. No remedial post-completion treatments have been required, significantly reducing rig time and operator costs. Specifically, the operator saved on average two and one-half drilling days per each 8 ½ in. section. Accordingly, with a daily rig rate of US $80,000, the use of the BREAKDOWN/D-STROYER tandem helped reduce drilling costs $2 million just for the 8 ½ in. batch intervals.

The 8 ½ in. sections of the 11-well project were batch-drilled to improve fluid economics and logistics. To boost production rates, the D-STROYER encapsulated oxidizer was added to the FLOPRO NT RDF formulation at a rate of 5 kg/m3 (1.75 lb/bbl). After reaching TD and circulating clean, the RDF was displaced to water. A pill comprising approximately 25 m3 (157 bbl) of BREAKDOWN breaker treatment spotted in the open hole at a density of 1.07 s.g. (8.7 lb/gal) prior to pulling out of the hole to rig-up the completion.

The BREAKDOWN pill was formulated with starch-specific enzyme and a chelant to degrade and dissolve the filter cake. Because of the mildly acidic pH (5.1) of the breaker pill, the D-STROYER internal breaker was activated to assist in the process of degrading the biopolymer content of the filter cake. No losses were observed while tripping and the operator successfully run in the hole with the completion string. Each of the breaker pills were mixed on location and displaced at 1,800 l/min (475 gpm).

The BREAKDOWN/D-STROYER tandem improved productivity on the gas storage well considerably, clearing the way for the operator to continue its 11-well program. Skin was slashed to a negative value, yielding excellent production rates with no post-completion treatment required.


Download: Spain: BREAKDOWN/D-STROYER Combo Slashes Skin Values, Optimizes Production Rate (0.39 MB PDF)

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