The Marnock Field contains four near horizontal gas condensate producers containing open hole dual wire wrap sand screens. Virgin pressure was 9123 psia but has dropped significantly on three wells to as low as 2200 psia. Reservoir temperature is 310°F. Pressure build up and material balance data showed limited inflow from the Marnock wells, and this was thought to be due to possible wellbore and sand screen mud blockage as only 50% of the drilling mud was recovered on initial well clean ups. Platform based stimulations were conducted in three wells to remove wellbore mud damage and potential sand screen mud blockage. Stimulation techniques consisted of a coiled tubing chemical placement from above the sand screens, a surface bullhead treatment and a coiled tubing sand screen jet wash. Barite attacking chemicals were deployed as the main treatment, including diversion for the bullheading operation.

Preparation, planning and execution of these stimulations have been complex given the potential to access un-depleted virgin reservoir pressure intervals. Well flow back and clean up post chemical deployment was critical and extensive chemical compatibility trials were carried out to ensure no damage to the formation or the process plant was incurred. A temporary clean up package including a high pressure cyclonic de-sander was used to separate flowback products and protect the process plant from solids contamination.

No significant well intervention operations had been conducted previously on the Marnock field on a non–rig basis apart from slickline operations. The challenges faced with installing and operating a full coiled tubing package including support tower and clean up package were substantial. Robust contingency measures were required to address the issues of stuck pipe, pipe cutting, well kill and high-pressure zones. Contingency innovations included the design and manufacture of an explosive cutter suitable for the heavy wall tapered coiled tubing. A special kill pill was also formulated for use with Cesium Potassium Formate in the event of a high-pressure well kill. Platform modifications were also required to enable the tie in of large diameter high and low pressure relief lines to the existing facilities.

As a result of the stimulations the Marnock Field has increased production potentials by 105 mmscf/d of gas and 6500 stb/d of associated condensate, equating to an increase of 25,000 boe/d.

You can access this article if you purchase or spend a download.