A newly developed high-pressure jet wash system field tested for Talisman Energy in a three-branch multilateral well displayed favorable results with respect to operational and treatment effectiveness. Operating parameters clearly demonstrated that the system was performing correctly. Treatment effectiveness was also proven, with all legs efficiently and effectively treated, resulting in increased well production. Additionally, time and costs were reduced by 50% by cutting the number of trips into the well to one from an average of three that had been required with previous methods.

The Blaster MLT, developed by Schlumberger is able to find each lateral and then effectively treat the reservoir through a high-energy jetting tool. The entire cycle can be repeated for all laterals in a multilateral well bore, which can most always be accomplished in a single trip.

Existing treatment methods

Multilateral wells provide optimal recovery of reservoir pay, which can be even more prolific with stimulation or cleanout treatments. However, developing a method to effectively treat and stimulate multilateral well bores has proven to be economically and technically challenging.

Previous methods included problems locating all legs of a multilateral well, extra trips and time on the drilling schedule, together with uncertainty of the treatment benefits.

The need for a better way of treating and optimizing production for multilateral well bores was evident, and was relayed by Talisman Energy, a Canadian company that routinely makes new multilateral, openhole completions. The company recognized the value in using the high energy jetting of acid to remove drilling damage from the rock face and restore permeability, often to its native state. The historical success of this technique in carbonate reservoirs made it the completion preference for many area operators. The advantage of a high-energy scouring on one leg was seen as being worth the cost and risk of an extra run in hole. However, Talisman believed that a new solution could be developed that reduced these risks and costs, while effectively and cost-efficiently conveying treatment acid to complete and restore its multilateral well bores. Having an integrated system to enter and treat all lateral legs with a high-energy acid scouring in one run would greatly increase not only the likelihood of improved production and recovery, but also associated project economics.

Developing and testing the system

The particular system to be developed needed to effectively treat the wellbore rock face of multiple laterals and thus optimize well production and project profitability. The result is the Blaster MLT service, which pairs the hole-seeking capabilities of a multilateral tool with the effectiveness of a high-energy jet wash tool to convey the treating acid onto the rock face formation (Figure 1). Pairing these two technologies into a multilateral/fluid jetting technique offers a main advantage of more effective stimulation and hole restoration in multilateral well bores compared to previous methods.

After the design phase of the multilateral jet wash system was completed, yard tests were conducted at test facilities in Rosharon, Texas. Various tests were performed to determine system capabilities, develop operating parameters and outline operational procedures. This experimental data would later be compared to a theoretical model to aid in designing the tool for operation at specific flow rates. In addition to yard tests, a downhole test was undertaken to compare the surface results with a run to about 7,000 ft (2,135 m) in an actual well bore. With only minimal changes occurring between surface and downhole operations, the operating flow rates of the tool could be predicted with reasonable accuracy. In addition, plots generated during this test provided visual aids that identified periods when the system was operating only the multilateral tool or the high-energy jet wash tool (Figure 2).

Following the standard qualification tests, more rigorous tests were performed consecutively to evaluate tool endurance and determine the robustness of the design. These tests were conducted with freshwater, nitrified fluids and nitrogen. Both circulation and nitrogen rates were increased and decreased for the duration of the tests while monitoring closely for signs of tool failure. When testing was completed, tool operation was still repeatable within ±1% of the initial operation parameters. No damage or movement of tool body joints were visible upon inspection and disassembly of the tool.

Applying and evaluating the new system

The multilateral high-pressure jet wash service was first implemented for Talisman Energy on a multilateral oil producer (Well #9) completed in the Rundle formation in the Turner Valley field. The openhole completion consisted of three well bores, two of which were sidetracked from the main leg. The well's total vertical depth measured 8,888 ft (2,709 m), with the longest lateral leg extending out to 11,387 ft (3,471 m). Essentially, the job consisted of a standard hole restoration using an acid-based treating fluid, but with the procedure modified to use the integrated system for administering the acid and treating each leg separately, while attempting to complete the job in one trip.

The BHA was rigged up and run to bottom of the intermediate casing. From there, the multilateral jet wash tool was run into each of the openhole legs. To determine the tool location, the depth of each leg was correlated with the known depths when bottom was reached. In each leg, the integrated system was activated and the high-energy jet wash tool was energized.

The multilateral component of the system was used to find and enter two of the three lateral legs, confirming that the hole finding capabilities of the integrated system were fully functional. Leg number 3 was the first to be entered and did not require the use of this component. Operational capabilities of the high-energy jet wash tool were confirmed with the sharp rises in circulation pressures when energized. Confirmation of continued operation throughout each lateral segment was made by a higher circulation pressure measured when comparing circulation pressure before and after activation at a given flow rate (Figure 3).

The entire system was then removed and inspected at surface, with no indications of tool failure in any of the components involved. From the operational side, all circulation pressures and flow rates indicated that the system performed as expected. With respect to the treatment, all treating fluid was conveyed onto the formation in the most effective way possible, with no down time. The entire job was completed within two days and in one trip, including rig up and rig down.

Summary

Trial field tests on Talisman's well #9 proved the accurate placement of acid treatments in three individual laterals, thereby treating this multilateral oil well as effectively as possible. This method increased the efficiency of the overall treatment by requiring only one run into the well bore and thus reduced the time to bring the well on production. Since this first field test, four more wells have been treated without incident. The implementation of the Blaster MLT service will greatly aid in the further development and production improvements of the Turner Valley field and holds much promise for similar fields in the area.

Editor's note: This article is based on SPE 94370, which was originally presented at the 2005 SPE/ICoTA Coiled Tubing Conference and Exhibition held in The Woodlands, Texas, USA, 12-13 April 2005.

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