The perforation strategy of Dynamic Underbalance (DUB) created the surging effect to remove debris from the perforation tunnels, thus reducing skin for optimal injectivity in this offshore development water injector well in Malay Basin, Offshore Sarawak. The objective was to inject up to 18,000 bwpd for pressure maintenance purposes. In the design phase, perforation software was used to perform the simulation iterations by sensitizing on the number of empty tubing conveyed perforation (TCP) gun chambers added at the top and bottom of perforation intervals. However, due to small gun size (4-½ in.), limited rat hole length and high static underbalance (1,000 psig), the desired amount of DUB using conventional empty gun volume only was not possible to be achieved. As a result, an innovative approach using two Pressure Operated Tester Valves (POTV's) was proposed, to create additional empty space inside the tubular between the POTVs above the packer. However, this created additional challenges which had to be overcome. Presence of empty tubulars in between the POTVs prevented the required hydraulic pressure transmission through the tubulars to activate the perforation guns via normal hydraulic TCP firing head. Therefore, a specialized firing system was required, which consisted of an acoustic communication system triggering downhole electronics to actuate a standard TCP firing head (Top-Fire Dual) - a first for this type of firing head. The POTV was activated by applying a pre-set annular pressure. Opening lower POTV, after the perforation fired, will create the required DUB surge, around 1,000 psi, which help cleaning up the perforation tunnels. Downhole fast gauges (recording in microseconds range) were run as part of the assembly to measure and to confirm the created DUB effect. Both fast gauges as well as acoustic gauges confirmed that 300 psi DUB was created upon gun firing and around 1,000 psi surging was achieved after the two POTVs were opened. Maximum losses recorded at 525 gallons per minute were observed following perforation. The well's injectivity performance was evaluated by performing step rate test and the result confirmed the well was able to meet higher injection rate than the plan.
The use of oriented perforation as a means of sand control technique has been adopted by many operators in industry. Two low angle wells completed in D field offshore Sarawak, Malaysia with moderate to weak rock strength quality required this method not only to limit the sand production but also to sustain the minimum production of 2500bopd each. Based on onset sand production analysis, reservoir M is predicted to have sand production in the direction of a maximum stress of 135degrees from true north. The wells then are suggested to be shot 0-180degree parallel to maximum stress and it saved the expense of no installation of downhole sand exclusion. This paper outlines the perforation analysis conducted to design the optimum perforation using Tubing Conveyed Perforating (TCP) Gun with Dynamic Underbalance (DUB) that effectively clean the newly created perforations. The operational approach applied to overcome the challenge of achieving desired orientation in almost vertical deviation wells by positioning electronic gyroscope siting on Universal Bottom Hole Orientation (UBHO) sub is also discussed in this paper. The available centralization solutions in market are limited to 30° degrees well inclination with 5°accuracies at three times more cost than conventional TCP. The proposal of oriented perforation at both slanted wells significantly saved lot of project economic and proved as effective sand control method, so far the production target is achieved and maintained with no record of sand production at field. Two newly drilled and completed wells located in offshore Sarawak, Malaysia required oriented perforation with dynamic underbalance using Tubing Conveyed Perforating (TCP) guns. The reservoir quality was weak to moderate rock strength with expected sand production in the direction of a maximum stress (135 degrees from true north) within the nearly vertical wellbore. To limit the sand production, the requirement was to shoot 0-180 degree guns parallel to maximum stress, to save the expense of any sand exclusion method. Another requirement was to use Dynamic Underbalance (DUB) to properly clean perforations, reduce skin, and maximize production. The objective was to achieve a minimum production of 2500 BPD. From Geo-mechanic study, in deviated well, the orientation of perforation is aligned with the trend of maximum horizontal stress. Based on breakout analysis, Shmax direction is 135° from the North. The expected production rate can be achieved with Oriented Perforation even at 0 deg phasing and PI reduced from 55 STB/day/psi to 38 STB/day/psi based on Figure 1 below. The studies conducted on Field D available data concluded that sanding risk is very low with Cased & Oriented Perforation strategy.
The total length of horizontal wells increasingly exceeds the normal running limits of coiled tubing (CT), therefore the industry has invented and adopted the use of water hammers to emplace the coiled tubing and its related equipment into the farthest reaches of the lateral (toe). This equipment can include hydraulic jets, mills and motors for cleaning debris out of the well, and tubing conveyed perforating (TCP) systems (guns with firing heads) for establishing the first initial flow path into the well for fracturing and production. From a safety perspective, the use of perforating systems, which contain several types of discreet explosive components designed to fire based on impact (some more sensitive than others), may conflict with the use of water hammers, which axially impact the lowest components of the bottom hole assembly. Sometimes the industry requires this combination in extended reach wells, especially before formation breakdown where no flow path exists for pumping down wireline perforating guns, and when primary completion equipment (sliding sleeves) fails. Modeling tools may allow users to configure tool strings with coiled tubing, water hammers, and perforating guns however this does not take into account the compatibility aspects regarding whether this is safe to do so. To truly determine the compatibility beyond simple conjecture, testing is required and has been completed. Laboratory testing of an industry-leading water hammer run above a typical coiled tubing and TCP assembly (toe gun) was carried out to determine the effect of accelerations (G's) and long-term related vibrations (~100,000 cycles) on safety-critical TCP system equipment and simulated explosives. A field trial using live explosives was successfully completed, confirming the test results. A novel approach, part of which is patented (Henke, 2010) is also described in which TCP equipment is configured with a fluid bypass to allow deployment on coiled tubing above a water hammer, hydraulic jets or mills and motors. This approach improves operator efficiency by allowing the clean-out and TCP system equipment to be run in a single trip. Laboratory testing measuring accelerations (G's) and long-term related vibrations (~100,000 cycles) again proved that there is no detrimental effect on safety-critical TCP equipment to include the shear pin in the firing head and liners in the perforating charges. Field testing of this system is pending.
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