Kristin is an HPHT gas condensate field which presents challenges at all levels. At present no solution is ready with regards to drilling in depleted reservoir, which means that most wells have to be drilled before production start. This results in a very limited production experience (well test at low rate) between the completion of each well.
Initially the Kristin field was planned completed using a stand alone screen solution and cesium formate based drilling and completion fluids. However it soon became clear that an additional completion solution and an alternative completion fluid needed to be evaluated.
Due to operational constraints overbalanced perforating was the only feasible solution and work was started to qualify a fluid system for this use. Different drilling fluids had already been tested for formation damage with regards to screen completion, and from this selection an oil based mud and a cesium formate based mud was chosen for further testing with regards to perforating. This testing was performed on an analogue rock to the Kristin reservoir emphasizing on rock strength and permeability as key indicators.
The preferred fluid was found to be oil based mud, and this fluid was recommended as perforating fluid for the first well to be perforated in the Kristin field.
Well 6406/2-R-3 H was perforated overbalanced in 2.06 sg oil based mud, April 2005 and subsequently cleaned up towards test equipment on the drilling rig.
This paper describes the work done to prepare and qualify a suitable perforating fluid for HPHT conditions, while trying to minimize damage. Furthermore the results from the test of the first well perforated overbalanced is described.