The Cupiagua retrograde Gas-Condensate reservoir, in the Llanos foothills of Colombia, was developed using a fast-track approach to provide production against an aggressive delivery plan. Unfortunately, an unusually severe condensate-banking effect combined with difficult perforating and drilling induced damage, meant that deliverability of the wells failed to achieve the desired levels.
This paper describes the approach that was taken to economically remediate these multiple-stacked reservoirs by the novel deployment of a through-tubing Frac-String. In addition, due to the highly tectonic regional-stresses, the final variant of this through-tubing frac-string was designed to permit surface treating pressures of up to 18,500 psi.
This solution was primarily possible due to the mono-bore completions with which the Cupiagua field had been originally developed. The frac-string was deployed through tubing with open perforations on the annulus; in addition variants, such as a slim-hole frac-string, allowed deeper zones within smaller production-liners to also be stimulated. The technology of the Frac-strings was incrementally developed over time and in this way new and more increasingly complex challenges could be undertaken without dramatically increasing the overall risk on each treatment.
More than 136 deployments of various string variants have been performed successfully; and even though annular tool clearances have been as low as 1/20" there has not been a single stuck-pipe incident to date. Throughout these operations the frac-string pressure test history has been faultless and the cumulative proppant placed during the frac treatments has amounted to more than 6,250,000 lbs.
Finally, significant production increments have also been achieved, the first well increased in productivity from ca. 8,000 bcpd to 18,000 bcpd and numerous low delivery wells were stimulated into becoming major producers. Individual case studies will be presented to support this, along with the production histories of the first 3 treatments.
Remedial treatments, of these deep tectonic wells, have been economically feasible due to the ability to deploy a frac-string through the existing completions. Variations on the actual rig-up, deployment and design have allowed economically less favourable wells to become feasible candidates. In addition, the continued field development, extension and infill drilling has also been made possible by the application of this novel approach.