A non-rig Coiled Tubing Unit (CTU) cement squeeze technique has been developed and proven in the Prudhoe Bay field. This new technique does not Prudhoe Bay field. This new technique does not require that the well be killed. The channel and perforations remain clean and unobstructed allowing perforations remain clean and unobstructed allowing easy placement of cement. This process utilizes in-situ contamination of cement left in the well bore after the squeeze. The contaminated cement is then circulated or reversed out of the wellbore after the squeezed cement has set, eliminating the need for drilling. The technique has been used to shut off channels in the primary cement to both the aquifer and the gas cap, to squeeze off unwanted production perforations, and to alter injection production perforations, and to alter injection profiles. Workover costs for these types of jobs profiles. Workover costs for these types of jobs have been reduced an average of 85% by utilizing the CTU technique. Scale modeling, full-scale testing, and field operating experience were drawn upon in developing this technique.
Thus far, 750 development wells have been drilled and completed in the Prudhoe Bay field. Nearly all of these wells have penetrated the gas cap and/or the aquifer as well as the oil producing sandstones of the Saddlerochit formation. Typical Prudhoe Bay completions have 9.625 in. production casing or a 7 in. production liner set at total depth, with 5.5 in. production tubing and a 4.5 in. tailpipe set to a depth just above the producing interval. The large casing sizes combined with high deviations have led to primary cement problems. Remedial cement squeezes, utilizing an arctic workover rig, have consistently resulted in severe formation damage when conventional high pressure methods are applied. With conventional rig squeezes costing an average of ﹩1.4 million, it was recognized that significant cost savings could be achieved if an alternate method was developed.
A CTU squeeze technique has been developed at Prudhoe Say which allows effective squeeze Prudhoe Say which allows effective squeeze operations and minimizes formation damage while realizing significant cost savings. The initial approach in developing this technique was to use standard field cementing practices when designing the first two CTU squeezes. Although the results of these operations were successful, it became apparent that further research was needed to optimize the procedure. Laboratory and model studies were implemented to better understand coiled tubing squeeze mechanics.
This paper outlines the results of this work and provides a systematic approach for design and provides a systematic approach for design and implementation of a CTU squeeze. The technique has its greatest application where rig mobilization costs are high such as offshore or Arctic locations. This method, which utilizes relatively small volumes of cement combined with low pressure techniques, assures minimal formation damage.
Two wells were CTU squeezed during the summer and fall of 1983. The first well had a channel to the aquifer. Production perforations had already been opened, but the well would not flow because of a 95% water cut. Squeeze perforations were shot into the channel below the producing perforations. A 6 bbl balanced plug of cement was placed on a gel retainer system with a CTU and squeezed using the Bradenhead method. A decrease in water cut was realized after this squeeze. After several repetitive attempts, the water was shut off completely by placing cement across the lower production placing cement across the lower production perforations and squeezing. post squeeze production was perforations and squeezing. post squeeze production was 5,000 BOPD, 0% water cut, but the lower zones were left covered with cement.
The second well selected for a CTU squeeze produced 3500 BOPD but had a GOR of 13000 scf/STB due to a channel from the gas cap.