This paper presents a detailed case study of a successful foamed HF treatment performed on a well in Block L2 of the Dutch Sector of the North Sea. The following technical difficulties had to be overcome during the design phase:

  • Because CaBr2/CaCL2completion brine, K2CO3 packer fluid, seawater, and potassium-magnesium (KMg) mud had leaked into the formation, the most appropriate HF blend had to be selected. Severe incompatibilities exist between these fluids and HF.

  • A corrosion inhibitor had to be identified that could provide adequate corrosion protection on 13Cr tubulars at a high bottomhole temperature (BHT) of 158°C.

  • Sufficient acid volumes had to be effectively placed across a large interval of 45 m. The cost of disposing returned fluid was also an important consideration, since the treatment was performed on a zero-discharge platform.

Operational difficulties included ensuring that appropriate handling procedures were established for the chemicals used and minimizing the risks of discharging pollutants into the marine environment and exposing personnel to chemicals. In addition, the stimulation treatment was planned as a concurrent operation (other wells on the platform were not shut-in during stimulation) to improve the overall cost-effectiveness of the project. This operation required detailed safety and operational procedures to be established before the treatment was approved.

This paper will discuss the numerous core flow tests and corrosion tests conducted during the planning phase along with treatment design philosophies. The paper also evaluates the performance of the treatment and presents postjob evaluations. These evaluations will include detailed returned-fluid analyses (which focus heavily on the corrosion inhibition aspects of the treatment) and Kinley microscopic caliper examinations of the tubulars after acidizing. The difficulties in optimizing a high-temperature corrosion inhibitor package will be discussed.

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