A brown field producing mainly from two main reservoirs, currently experiencing low reservoir pressures and high GOR ranging 400-1000 psig and 2000-20000 scf/stb respectively with about 17% average water cut. Re-perforation and adding new perforations are one of the key production enhancements activities for this field.
Two candidates were identified for additional perforation opportunities. Nodal analysis evaluation study based on reservoir parameters (permeability, water saturation, reservoir thickness) suggested oil can be gained by executing these opportunities.
The main issue in executing the perforation job was that the proposed perforation intervals are covered by 3 barriers which are the 2–3/8"tubing, 7" and 9-5/8" casing. Technical simulations and practical surface tests were performed to verify the integrity of the 2-3/8" tubing, and when shooting in multiple casings (7" Liner and 9-5/8" Casing). These tests were done to select the proper gun type, size and phasing (shot density) due to the limitation and risks associated with the through tubing perforation. The gun selected after the study was 1–11/16" strip gun with 2 SPF and 0 deg phasing.
The through tubing additional perforation jobs were executed with 20 ft and 135 ft for the two highly deviated (60-70 deg) candidate wells. These were the first job for PETRONAS Carigali in through tubing perforation through three barriers of tubing, liner and casing.
Very good results were achieved, where oil production increased by about 300 bopd and 200 bopd for the two wells respectively, and the WC% decreased from 45% to 0% for the first well due to higher reservoir pressure of the upper zone.
The successes of this application can enhance re-looking to many wells that have additional perforation ignored initially due to covering by tubing plus multiple casing which result in increasing oil production.
This paper shares the details of the well, the nodal analysis carried out to quantify the possible gain, the preparation for the yard tests and the evaluation in the gun selection.
