Successful Application of Foamed Acid Stimulation on a Severely Perforation Damaged Horizontal Well with Perforations Behind Tubing
- Warakoon Ruksanor (Sakhalin Energy Investment Co. Ltd.) | J. Webers (Sakhalin Energy Investment Co. Ltd.) | E. Vargas (Sakhalin Energy Investment Co. Ltd.) | R. Gdanski (Shell International Exploration and Production) | S. Vickery (Shell International Exploration and Production)
- Document ID
- Society of Petroleum Engineers
- SPE Russian Oil and Gas Exploration and Production Technical Conference and Exhibition, 16-18 October, Moscow, Russia
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 3.1.6 Gas Lift, 1.11 Drilling Fluids and Materials, 4.1.2 Separation and Treating, 2.2.2 Perforating, 4.6.2 Liquified Natural Gas (LNG), 2.2.3 Fluid Loss Control, 3.2.4 Acidising, 2.5.2 Fracturing Materials (Fluids, Proppant), 2 Well Completion, 5.4.2 Gas Injection Methods, 4.1.5 Processing Equipment, 2.3 Completion Monitoring Systems/Intelligent Wells, 5.1.2 Faults and Fracture Characterisation, 4.2 Pipelines, Flowlines and Risers, 3 Production and Well Operations, 4.2.3 Materials and Corrosion, 5.2 Reservoir Fluid Dynamics, 1.8 Formation Damage, 5.6.3 Pressure Transient Testing, 2.4.3 Sand/Solids Control, 5.4.10 Microbial Methods
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Well LA-552 is the first Lunskoye horizontal oil rim appraisal/producer well targeting the oil rim underneath the Daghinsky gas reservoir. The well is a smart well completion having three zones (one gas zone for auto gas lift and two oil zones) remotely controlled by three inflow control valves (ICV's).
Pressure transient analysis on production data indicated a very high Darcy skin factor causing much lower production than expected. This was predominantly caused by overbalanced perforating with an oil-wet calcium carbonate (CaCO3) fluid-loss control pill used in the production liner.
Due to the well configuration, the damaged zones were not reliably accessible by wireline or coiled-tubing making re-perforation or acid jetting very difficult and risky. Without well recompletion, the only remaining option was to pump acid down the tubing through the ICV's to dissolve the pill across the long perforation intervals of both oil zones (approx. 200 meters long for each zone).
Zonal coverage (diversion) was expected to be a major challenge for an acid remediation treatment, since the perforations were behind tubing and accessible only through the ICV's. Various diversion methods were considered. Foam diversion in combination with a slow reacting acid system was selected to ensure zonal coverage.
An extensive series of lab tests were performed resulting in an acid blend of 9% formic acid containing 7% KCl (temporary clay stabilizer), 2.5% mutual solvent, 0.6% corrosion inhibitor, 15 lb/Mgal inhibitor aid, and 2% foamer being recommended for removal of damage believed to be oil-wet carbonate filter cake. The recommended acid was qualified as having passed oil-wet carbonate filter-cake dissolution tests, mud and oil compatibility tests, corrosion tests, and foam stability tests.
The acid stimulation was successfully performed in September 2011 with the following result:
- Net oil production increased 2.5 folds at 20% water cut (same as pre-stimulation)
- Major improvement of upper zone. Darcy skin reduced by 10 folds and productivity index (P.I.) increased by 4.3 folds.
Limited success for the lower zone. P.I. increased by 54% but no significant improvement seen in Darcy skin. The limited success of the lower zone could be explained by a combination of low injectivity (0.5 bpm) and operational challenges causing sub-optimum foaming.
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