Published: 07/08/2008
Published: 07/08/2008
The Tengiz field in Kazakhstan is a large carbonate reservoir in which zonal coverage during acid stimulation of wells is a significant issue. Conventional stimulation methods tend to inject acid only into the higher permeability layers or the first stimulated zones.
The primary method that Chevron used for stimulating Tengiz field wells was to inject 15% HCI conveyed by coiled tubing (CT). Spotting the acid in front of the different reservoir layers provided diversion.
Laboratory results have shown that viscoelastic diverting acid systems provide diversion during stimulation of limestone reservoirs. Based on these results, Schlumberger used the VDA system to stimulate eight wells in the Tengiz field. Production logs and pressure tran- sient tests were performed before and after stimulation to evaluate the results.
All eight wells stimulated with the VDA system showed a significant increase in production and achieved a high negative skin value. The prestimulation average production rate was 52,030 bbl/d and the poststimulation average production rate was 123,670 bbl/d—an increase of 238%.
Production logs showed that the system was able to divert part of the acid from the most permeable zones to the other zones, achieving full zonal coverage.
Treatment results indicated that the VDA system
All eight wells stimulated with the VDA system showed a significant increase in production and achieved a high negative skin value. The prestimulation average production rate was 52,030 bbl/d and the poststimulation average production rate was123,670 bbl/d—an increase of 238%.
Challenge: Improve zonal coverage during acid stimulation and increase oil recovery.
Solution: Use the Schlumberger VDA viscoelastic diverting acid system to create diversion and stimulate previously unstimulated zones.
Results: Increased production by an average of 238% - and achieved full zonal coverage - in all the treated wells.
