Offshore developments have long outweighed the costs of onshore developments, but they come with the potential promise of larger production and well longevity. The search for the best price-to-performance ratio has led operators to seek the ideal solution that is inexpensive and operationally efficient, yet effective for every reservoir, including offshore, Fig. 1.
A new and novel idea is not always the answer when it comes to innovation, especially when risk is involved. On occasion, it’s the amalgamation of existing ideas that results in something not only innovative but incredibly valuable. This was the case for the combination of horizontal drilling with multi-stage hydraulic fracturing systems. The combination was an inspired pairing that unlocked the unconventional industry that exists today.
In recent years, another inventive pairing has evolved from horizontal multi-stage completions. The integration of high pressure / high temperature (HPHT) and offshore capabilities with multilaterals has the potential to increase efficiency and create additional value for operators worldwide.
INTERVENTIONLESS SLEEVE COMPLETION TECHNOLOGY
In the early 2000s, sliding sleeve technology was introduced, and it took the market by storm. The efficiencies of ball-drop technology allowed operators the ability to complete their wellbores with more stages in a drastically reduced timeframe than they currently were experiencing. The proficiency of dropping balls from surface to open the sliding sleeves resulted in continuous pumping operations, with minimal transition time from zone to zone.
Prior to ball-drop technology, operators were spending multiple hours transitioning from one zone to the next. The operation would include running tools from surface on wireline or coiled tubing for each stage. As time went on, operators saw the economic benefit to increase the stage count beyond what they were currently doing, both with traditional completion techniques and ball-drop technologies. This resulted in an ongoing engineering pursuit of increasing stage counts by a variety of different techniques.
As the stage counts increased the value that ball-drop technology provided, they also increased the ability to save multiple days per stimulation. Major advancements were made, regarding ball technology, including changing the strength and composition of the balls. By increasing the strength of the balls, the stage counts increased to meet and exceed the demand for higher stage counts.
The next significant step was the development and use of degradable materials for construction of the actuation balls. The ability to have a ball degrade downhole after the stimulation was another substantial advancement in the efficiency of ball-drop multi-stage technology. This eliminated the need to remove the balls from the wellbore prior to production, either by milling or flowing the balls back to surface.
Engineering evolutions pushed the ability of multi-stage fracturing technologies continually. In parallel with development of the sliding sleeve and ball technology, open-hole packers were designed to allow for higher treating pressures. Innovation in elastomer and element design advanced to allow operators to have working pressures up to, and beyond, 15,000 psi.
Multi-stage ball drop technology has been used in multiple offshore environments, including operations in Congo, Gabon, Romania, Vietnam, Saudi Arabia, United Arab Emirates and the North Sea.
A multilateral well consists of a well with two or more laterals drilled from a main motherbore, Fig. 2. This method of well construction was developed as a way to add value by minimizing the costs of accessing a reservoir by utilizing the same vertical section.
Junction technology has a broad range from open-hole junctions to much more complex and costly junctions that allow the well to be fully cased and/or cemented into each lateral. The junctions have been categorized by the Technology Advancement of Multilaterals (TAML) into levels ranging from one to six.
For onshore-based wells, where operators were drilling multiple pad wells, the drive to increase efficiency and maximize revenue was a constant target. A cost comparison was completed, comparing two wells against a multilateral well, to determine whether there were economic advantages.
Packers Plus worked with operators to develop a simple and repeatable technology that would allow for multilaterals to be completed with multi-stage ball-drop systems. After successful field trials, this led to a technology that quickly accumulated a track record of 1,000+ multilateral completions, Table 1. The technology was used widely across the Western Canadian Sedimentary basin, allowing Packers Plus to gain valuable experience in both the design and installation of these open-hole, multilateral, multi-stage completions.
Along with the lower oil prices of the mid-2010s came some shifts in the way that offshore wells were being designed and completed. The efficiencies that transformed the North American shale development were now being looked at to see what technologies could be adopted for offshore well construction. Technologies that provided the ability to reduce costs without adding significant risks were being analyzed to determine their value. This led them to find the option of developing multilateral wells with a simple, low-cost junction in combination with open-hole multi-stage completions.
TWO OFFSHORE CASE STUDIES
World’s first offshore dual-lateral multi-stage completion. An operator in the United Kingdom, focused on oil and gas operations in the North Sea, was seeking a low-cost completion solution for its offshore development. With multiple target reservoirs in the same area, the operator required a solution to maximize stimulation effectiveness and minimize cost.
To provide the most cost-effective technology solution for the project, the Packers Plus team designed for simplicity. Using a TAML level 2 multilateral junction and proposing the same straightforward and proven StackFRAC® HD design for each leg, the completion would be able to access two separate reservoirs from a single wellbore.
The dual-lateral project was designed with two identical 5.5-in. 14-stage StackFRAC HD systems, Fig. 3, including key considerations such as:
- Reservoir characteristics and stress profile through the laterals
- Choice of fluid, volumes and timing to maximize fracture propagation and area, and optimize wellbore conductivity
- Efficiency of using a full boat of acid per lateral as a large treatment, which would also minimize down time, due to sailing and reloading.
Once operations were complete for the motherbore, a whipstock packer was set, and the second leg was drilled. With over a year’s worth of planning and coordination, this offshore acid-fractured dual lateral was completed on schedule, and at lower than the estimated cost. Besides introducing the operator to operational and economic efficiencies, the well has already shown higher-than-expected initial production.
Offshore multilateral completion results in top producer. Having space for one last wellhead on an existing offshore platform, an operator working in the Black Sea was looking to maximize reservoir coverage with a multilateral well. The completion included a StackFRAC HD multi-stage system in each leg and was the first offshore multilateral completion in Romania.
The operator was familiar with Packers Plus’ extensive run history of onshore multilaterals and the success of an offshore multilateral project in the North Sea. In most multilateral operations, each leg is drilled, installed and stimulated separately. For this well, however, a more efficient system was implemented. With the drilling and installation of both legs completed first, the stimulation of both legs could be done consecutively.
After both legs were drilled and installed with six-stage StackFRAC HD systems, a specialized assembly was built to help navigate the upper completion string out of the window and into Leg 2, which was stimulated first, Fig. 4. The project was completed on schedule. Not only was this the first offshore multilateral in Romania, it also set a benchmark as the highest producing well in the operator’s portfolio after several months of production.
As with the combination of horizontal drilling with multi-stage hydraulic fracturing systems that began the unconventional revolution, the integration of HPHT/offshore-capable technology with multilateral completions will generate new interest for a variety of challenging environments around the world, including offshore reservoirs.
As shown by the success of the implementation of StackFRAC HD in the North Sea dual-lateral and the Black Sea multilateral, the industry is stepping toward the reality of lower risk, more-economic and high-efficiency multilateral completions in offshore wells.
Packers Plus is a completion technology company committed to providing high quality solutions for a variety of applications, including cemented and open-hole liners, HPHT, multilateral, onshore and offshore wells. To deliver this technology to the field, knowledgeable and experienced specialists provide customized solutions to clients around the world and are dedicated to ensuring the success of every well.
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