Swellpacker™ System Delivers Step Change in Zonal ... - Halliburton

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E A S Y W E L L Industry Challenge The field to be developed contains several reservoirs that share the general features of being deep, highly pressured and sour. Reservoir simulations for a major Middle Eastern Operator’s first EOR project in southern Oman indicate a significant increase in recovery can be achieved, but only by successfully isolating gas and water in the event that either or both breaks through prematurely to producing wells from the miscible gas injection wells. To obtain the additional reserves, zonal isolation is required, however, conventional cementing techniques have proven unsatisfactory. Cement bond logs run in every well showed in practically every case that a microannulus conductive to reservoir fluids had been created, preventing zonal isolation. Innovative cementing techniques to increase the probability of reliable zonal isolation and minimize expensive workover operations are required. Halliburton Solution Combining oil-swellable elastomer technology (Halliburton’s Swellpacker isolation system) with a primary cementing job provides an effective means of addressing microannulus concerns and incomplete cement sheath issues. This is a technically viable option to meet the EOR project’s stringent zonal isolation requirements in the event the cement debonds from the casing and hydrocarbons attempt to flow through the microannulus. Instead of the hydrocarbons conducting, they instead activate the swellable elastomer upon contact; because the swelling rubber element can conform to almost any irregular geometry, it can swell to close the microannulus and thus reestablish the hydraulic seal required. To ensure an effective annular seal between multiple reservoir layers, the Swellpacker isolation system can be installed as part of the production liner. It can also act as a backup in the event that a microannulus is created at the cement/liner interface. Operator Results The Middle East field to be developed consists of nine reservoirs, each with distinct characteristics. In general, the reservoirs are deep and highly pressured and they contain sour, light hydrocarbons. More than 50 wells have been drilled in and around these fields. The initial wells have a shallow 13-3/8-in surface casing, a long 9-5/8-in production casing and a cemented 7-in liner over the reservoir section. They are completed with 3½-in tubing and some have a permanent downhole pressure gauge. HAL9422 1
The cluster is being developed in three phases. The objective of Phase 1 was to determine from a number of data sources whether a miscible gas injection project would be feasible in some fields. Phase 2 will involve primary depletion in a number of fields followed by gas injection in some of them. Phase 3 will involve formation-wide depletion and gas injection in the remaining fields. To maximize ultimate recovery from these fields, gas (and water) shutoff is required during Phase 2 and Phase 3 of the project. Therefore zonal isolation over the reservoir is essential. A substantial effort was made during Phase 1 to determine whether zonal isolation was being achieved using conventional cementing techniques. Cement bond logs were run in every well over the liner section to determine the quality of cement. These logs showed in practically every case that a microannulus had been created. During well completion, cement from the production liner debonded because of differential pressure, leading to the creation of a microannulus. Subsequently, the cement cannot re-seal and a permanent flow path between cement and production liner may arise, preventing zonal isolation. Selective perforating during the well testing campaign showed that this microannulus was conductive to reservoir fluids. In one incident, reservoir fluids leaked all the way to surface, providing further evidence of inadequate zonal isolation. Expandable pipe was not a technically feasible option owing to the presence of high levels of hydrogen sulfide. A focused effort was initiated to find an improvement over conventional cementing techniques, and attention settled on the Swellpacker isolation system. Laboratory testing To determine if the Swellpacker isolation system would be able to withstand the anticipated differential pressure levels in the various reservoirs, laboratory testing preceded a field trial. Testing aimed to verify the cement assurance principle of the Swellpacker isolation system with a 2-m-long, 4.82-in outer diameter (OD) rubber element on a 4.5-in OD base pipe placed in a 4-m-long, 6.1-in OD autoclave. The sealing ability of the Swellpacker isolation system was tested by introducing a microannulus on one side (90°) and allowing the rubber element to swell and seal off the annulus by flowing hydrocarbons through it. The pressure test was aborted at 300 bar (maximum pressure rating of the test unit) and the Swellpacker isolation system was able to hold the differential pressure with no detected leak. The system proved to be effective in sealing off a simulated microannulus between the cement and pipe interface and could withstand a differential pressure in excess of 300 bar. The test also demonstrated that the Swellpacker isolation system sealed off irregular surfaces at the cement edge. These results provided confidence that the Swellpacker isolation system can effectively seal off a microannulus that develops downhole between the pipe and cement interface—for example, as the result of operations during well construction. Field trial It was therefore decided to run a field trial of the combination of a cement slurry with the Swellpacker isolation system. The objective of the production test was to expose the Swellpacker isolation system to oil and then to measure changes in flow rate, fluid composition and static pressure. The critical parameters to be tested were as follows: 2
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Swellpacker™ System Delivers Step Change in Zonal ... - Halliburton

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