RIASSUNTO
Abstract
Recently a contaminated cement squeeze was performed in the Gulf of Mexico using coiled tubing. The work was performed at 18,600 ft, 326°F bottom hole temperature, 12,000 psi pumping pressure and 9,000 psi chokeback pressure in a H2S, CO2 environment. Operationally this squeeze was a tremendous success and set several new benchmarks with regards to high-pressure coiled tubing operations.
This paper describes the reasons for using a contaminated cement squeeze under these harsh conditions, the standard procedure for this work, and the deviations from standard procedure made specifically for this well. The paper also discusses the importance of hydraulic modeling, fluid selection, the benefits of doing yard tests, and analyzing previous jobs to verify the models.
Background
In 2001, the operator drilled an exploration well in Louisiana State waters just south of Marsh Island and Intracostal City in 10 ft of water. The well encountered many drilling problems, primarily lost circulation and geopressures. Through the use of lost circulation treatments (12 treatments were pumped) and additional casing strings, the vertical well was total depth at 18,703 ft md. A 4 1/4-in. hole had been drilled from 14,500 ft to TD using a 19.5 lb/gal synthetic oil-based mud system. Wireline logs in Figure 1 indicated over 70 ft of gasbearing sand on bottom and with a prolific water sand 84 ft above. A 3 1/2-in. production liner with a reamer shoe was reamed to bottom in 24 hr and cemented in place using 20 lb/gal cement without any returns to surface. Subsequently, a cleanout and tieback was performed, a packer was installed at 12,602 ft (with 32 ft of 1.968-in. throughbore), and 2 7/8-in. tubing was run from packer to surface. This left the well with the internal diameters of 2.323-in. to 12,602 ft, 1.968-in. to 12,634 ft and 2.75-in. to 18,703 ft as seen in Figure 2.
Well Test
The well tested with high initial rates of gas and condensate. Shortly into the test, water encroached upon the producing horizon and shut-off the hydrocarbon production. Water was produced in the test at rates higher than 10,000 bwpd. It was reasoned that the water production was coming from the zone 84 ft above the desired horizon through the primary cement job. The gas produced contained 15 ppm of H2S and 5% CO2.
Option Discussion
Several remedial treatments were investigated for isolating the producing horizon from the encroaching water production. The different options considered were:
Water Conformance Treatments
Bullhead Cement Squeeze
Coiled Tubing Contaminated Squeeze
Water Conformance Treatments
The well has a BHT of 326°F. The temperature coupled with the necessity to isolate the water zone without shutting off production from the gas sand ruled out the majority of the water conformance treatments.
Bullhead Cement Squeeze
This method would involve pumping cement from surface down the production tubing and squeezing the zone of interest and any channels from the producing zone to the water sand. The bullhead method posed several problems including the probability of leaving cement fairly high in the production tubing due to an early squeeze. This method would require the use of coiled tubing or snubbing to subsequently drill out the remaining cement in the wellbore. Pumping cement through the completion was believed to be possible but posed a drilling risk. Passing a coiled tubing milling assembly through a 1.968-in restriction and then drilling cement in a 2.75-in liner would require a 1 11/16-in drilling motor operating at 326°F, and using an under-reamer. It was believed that low motor life and therefore time required to drill cement, would be very high. In addition, in the event that fishing was required, it was believed that fishing in the 2.75-in. below the 1.986-in. restriction would be very difficult. The inability to fish the motor assembly below the 1.968-in. restriction increased the overall risk of losing access to the producing zone. Because of the high BHT, limiting the life of the motor and the risk of loosing the motor assembly due to the well restriction, a bullhead cement squeeze was not considered the best option.