New system makes high-rate pumping accessible and affordable in remote areas.

For years, offshore operators have relied on dedicated stimulation vessels for high-rate pumping operations such as hydraulic fracturing, frac packing and acidizing. Contracting these vessels can be extremely expensive, and they are not available in many remote regions. Baker Oil Tools recently introduced a modular, mobile stimulation pumping system called StimFORCE that provides the capabilities of a traditional, dedicated frac pumping vessel, in an integrated skid unit system. This equipment package can be shipped and reconstructed on a platform supply vessel (PSV), barge, or offshore rig to provide stimulation and sand control services in remote locations. By reducing or eliminating the need for a dedicated pumping vessel, the new, modular system lowers pumping costs and increases flexibility for operators. The first system was recently shipped to Equatorial Guinea to provide frac pack and gravel pack pumping services on an extensive, multiyear deepwater sand control completion project.

Meeting challenges

With the sustained higher prices of oil and gas, exploration and production companies are developing fields that require fracturing and pressure stimulation treatments in remote land, swamp and offshore areas where conventional stimulation services are not readily available. In remote offshore operations, operators often batch drill and batch complete, making for extended periods of time between completions. When a dedicated stimulation vessel is used for the completions it must remain in the area for the duration of the project, generating high costs for the operator, even when stimulation services are not being performed.

An evaluation of operators' stimulation and sand control needs, particularly for offshore areas, revealed that a modular stimulation plant design was required as an alternative to dedicated vessels. The stimulation plant needed to be easily shipped and able to be placed on a PSV or the rig.

Shipping, mounting and securing the equipment to the deck of the PSV provided many challenges. For global shipping, the units needed to be shipped in an ISO container box 8 ft wide, 91¼2-ft (2.8-m) tall and 10-, 20- or 40-ft (3-, 6- or 12-m) long and equipped with intermodal locks to comply with standard commercial freight rates and delivery schedules. A grid was required to secure the equipment to the deck of the PSV and to distribute the load-bearing footprint to not more than 1,020 lb per sq ft (4,980 kg per sq m). The deck securing grid design enabled rapid installation and removal of the equipment and flexibility in locating various units. This flexibility was required to provide access to sounding tubes and hatches, whose locations vary with different PSVs.

An additional requirement set by the design team was that certain units needed to be able to work from offshore platforms, rigs or drillships. In a survey of rig operators it was determined the units needed to weigh less than 35,000 lb (15,875 kg) in order for the rig and dock cranes to be able to lift and spot them on the PSV, rig floor or pipe rack. To meet most international operating companies' offshore rig lifting and operating requirements, the skid frames needed to be built and tested to Det Norske Veritas (DNV) 2.7-1 standards for dropping and be CE certified to European service requirements for electrical safety.

Stimulation plant

The basic components and fluid flow path of a stimulation plant are as follows.

•Control room, from which the stimulation operations are conducted and communications are provided by 24/7 satellite service;

•Field lab to perform quality assurance and quality control of the stimulation fluids;

•Below-deck holding tanks, from which conditioned potassium chloride fluid is transferred to the liquid additive system on the deck of the PSV. The PSV transfer pumps may require up-sizing to transfer fluid at the desired pumping rates;

•Liquid additive system (LAS), which meters liquid additives on-the-fly to the fluid stream;

•Hydration unit for gel fracturing fluids to give the slurried polymer concentrate time to hydrate;

•Proppant fracturing blenders, which add proppant and final liquid additives to the fluid stream before it is pumped downhole. After the proppant is added the slurry is transferred to the high-pressure pumps;

•High-pressure (15,000 psi /1,034 bar) fracturing pumps which pump the slurry into the high-pressure manifold and then flexible steel hoses;

•Flexible steel hoses at the rear of the vessel, which are hung off on the side of the rig. Slurry is pumped into the hoses from the frac pumps. The equipment package has two flexible steel hoses, one 3-in. inside diameter (ID) and one 4-in. ID, each 300 ft (91.5 m) long which are run from the stern of the vessel to the side of the rig and then to the frac manifold on the rig floor; and

•A frac manifold which is connected to the frac head on the work string where the slurry is conveyed down the drill pipe to the frac pack tool and formation.

A stimulation plant for acidizing consists of essentially the same components as for fracturing, except that the frac gel blending system is replaced with an on-the-fly acid blending system.

Modular stimulation plant

The capabilities of the modular stimulation plant were designed to meet current and foreseen operator requirements stimulation requirements, especially for deepwater frac and gravel packing. Backup systems were given high priority. The modular plant consists of a control room, field laboratory, storage containers, power packs, liquid additive system, hydration unit, two 45 bpm frac blenders, six frac pumps for 9,300 hhp and two 300-ft (91.5-m) flexible steel hoses. The system's treatment range includes frac pack completions up to 45 bpm at 12 ppa (pounds proppant added) and 50 bpm at 10 ppa, as well as low-rate openhole gravel packs requiring a maximum of 5 bpm at 0.5 ppa.

Above-deck proppant storage consists of several compartments for storage of 200,000 lbs (expandable to 300,000 lbs) of proppant, with below-deck bulk transfer connections for multiple treatment capability. "On-the-fly" mix capabilities minimize equipment footprint while using supply vessel or rig water for freshwater- or seawater-based treatment systems.

For installation, 22 grid panels, 8 ft wide by 40 ft long (2.4 m wide by 12.2 m long), are placed on the back of the PSV, locked together, then secured to the deck with turnbuckles. Next the stimulation equipment is placed on the grid locked to place with the same intermodal locks used for shipping. This securing system minimizes required vessel modifications and provides safe mounting for treatment equipment during extreme weather conditions.

Flexible stimulation

Modular stimulation plants can be easily installed and removed from an operator's platform supply vessel. The template requires a free deck area of 40 ft by 176 ft (12.2 m by 53.7 m). Location and climatic conditions determine what type of service vessel is needed. The system can also be configured for pumping onshore and from platforms, rigs and drill ships, meeting minimum footprint requirements. The modular design and flexibility in the equipment package permits it to be modified or changed if the completion type changes during the life of the project, for example, if the project moves from frac packs to openhole gravel packs or vice-versa, or if larger acid treatments are required.

The flexibility of modular stimulation makes it ideal for batch drilling and completion programs in remote areas. Instead of waiting for a dedicated vessel to travel to the drilling location, an operator can employ a supply vessel already in the area to transport equipment, completion fluids and other materials in addition to performing well stimulation operations. When the stimulation plant is not required, it can be stored at a land base location for a fraction of the cost of parking a dedicated stimulation vessel. When pumping is required again, the pumping system can be quickly reassembled. The "plug-and-play" capability of the components allows the service company to custom-tailor pumping equipment to the specific needs of a completion. This flexibility can result in substantial cost savings for operators.

First assignment: Equitorial Guinea

The company recently shipped the first system to an operator in Equatorial Guinea to provide frac pack and gravel pack pumping services on an extensive, multiyear deepwater sand control completion project. The project, consisting of producer and injector wells, is anticipated to require 80 or more completions throughout the next several years. The wells will consist of sand control completions with the service company's screens, frac pack tools and upper completion equipment. Because the sand-face completions will require primarily frac packs complemented by a few gravel packs, a stimulation plant with 200,000-lb proppant capability is required.

Economic and vessel availability prompted the operator to select a modular stimulation plant for this project. Installing a modular plant on the operator's PSV should result in substantial savings over contracting a dedicated stimulation vessel for the life of the project. Additionally, with long-term availability of a dedicated vessel uncertain, using a modular plant gives the operator full control over its use and availability, and provides assurance that there will be no need for deepwater rigs to wait for a dedicated vessel to run completions.

Finally, using a modular system allowed the tool company to build the equipment in the United States and then ship it via commercial freight and rates to the work site. The equipment design also allows the company the flexibility to de-mobilize the equipment at the end of the contract and transport it to another location, or store it temporarily while awaiting another contract.