Recently, the design program of the world’s largest and China’s first offshore well stimulation vessel independently developed by SDARI and made for the Tianjin Branch of CNOOC (China), has successfully passed the basic design review of CCS. The design and construction contract of the vessel has been signed, symbolizing that China has made a major breakthrough in the field of offshore fracturing technology and engineering, and has broken the long-term technology monopoly and blockade of foreign countries at one stroke. This is also another offshore oil and gas operation tool that China Shipbuilding Group and CNOOC have made great efforts to build by practicing China’s strategy of “self-sufficiency in oil and gas” and safeguarding national energy security.
The well stimulation vessel, which is highly integrated, automated, digitalized and intelligent, and whose overall performance has reached the world’s advanced level, will be built by Wuhu Shipyard Co. With an overall length of 99.9 meters, a beam of 22 meters and a depth of 9.9 meters, the vessel will meet the new demands for large-scale fracturing operations in the whole sea area of China, batch fracturing operations in multiple wells at sea, as well as gas wells and ultra-deep fracturing operations, which is of strategic significance for filling the gaps in the area of offshore oilfield fracturing technology and engineering in China.
The vessel is mainly used for the exploitation of potential reserves in offshore low-permeability oil and gas fields for the purpose of stabilizing and increasing production. After the drilling is completed, by injecting high-pressure acid (acidized fracturing) or sand-containing fluid (sand-added fracturing) into the wellbore, the pressure at the bottom of the well exceeds the fracture pressure of the formation, and a series of cracks are artificially created in a certain range of the reservoir in the wellbore, so that oil and gas in the reservoir can flow into the wellbore through these cracks and be extracted out of the ground. Fractured fractures have a certain width, and the oil and gas flow through them with little resistance, which is equivalent to a “highway” in the reservoir. Without artificial fractures, fluids from the far side of the wellbore would have to overcome the heavy resistance of the formation during seepage before entering the wellbore, which is a long way to go, and in some wells there is no production capacity at all without fracking because there is not enough energy to overcome this resistance. Therefore, in layman’s terms, a well stimulation vessel is a professional with superior fracking capabilities, which can maneuver to the target platform to carry out fracking operations and maximize the controlled reserves, cumulative production and overall recovery rate of a single well. For platforms with limited deck area (especially unmanned platforms), large-scale fracturing operations are no longer difficult with a fracturing vessel.
This type of well stimulation vessel has the following 5 advantages：
Strong fracturing operation capacity and high degree of integration. To meet the special needs of offshore fracturing operation, in addition to professional fracturing equipment, the vessel is also equipped with fluid supply equipment, mixing equipment, sand mixing equipment, sand storage and delivery equipment, other material storage and supply equipment, etc. All the specialized equipment for oilfield production enhancement operation is arranged in the cabin (in the main hull), which can effectively reduce the influence of the sea condition. The capacity of key fracturing equipment carried on board is the best in the world.
Safe and reliable. The vessel adopts the design of integrated power station, i.e. the fracturing equipment is highly integrated with the ship’s power consumption. The power distribution board of the integrated power station is divided into five sections of converging rows, so that in the event of the largest single point of failure, the ship’s power station can ensure that four fracking pumps, one sand mixing device and one mixing device can work at full capacity, which can effectively guarantee the safe conduct of fracking operations. Moreover, it can carry out fracking operation under the environmental conditions of Class 7 wind, 3 meters righteous wave height and 1.5 knots, and safely navigate under the environmental conditions of Class 8 sea state and Beaufort Class 10 wind.
Excellent propulsion performance. The ship adopts all-electric propulsion in a forward-looking way, equipped with two electrically-powered full rotary thrusters, one telescopic thruster and two bow thrusters, with a power positioning capability of DP level 2 and a sailing speed of more than 13 knots. The ship can also operate within a small radius, such as in-situ slewing and traversing, with excellent maneuverability.
Eco-friendly. The vessel adopts the electric propulsion “Closed Ring” circular closed busbar design, which can adjust the number of on-net units according to the load condition of the whole ship’s power grid when the ship is in DP operation, and improve the load rate of on-net engine units, greatly reducing the fuel consumption and emission. The ship’s generator set has no light load working condition and can keep running at full load all the time, and the efficiency of the diesel engine is kept at the optimal operating point, which effectively reduces diesel fuel consumption and pollutant emission and realizes green friendliness. The ship is also equipped with a domestic sewage treatment device that meets the latest regulations of the International Maritime Organization (IMO) MEPC to satisfy the emission control requirements.
High degree of intelligence and automation. The vessel is equipped with the Smartlink Service Cloud Platform and is highly integrated with the ship’s intelligent system platform, which has the functions of intelligent cabin, intelligent navigation as well as intelligent integration platform, realizing the digital operation of equipments and intelligent operation of the vessel, which makes the vessel more economical, safe and efficient. The vessel is equipped with a fracturing system command center and corresponding professional control software in the configuration of the electrical system, which can realize the monitoring and control functions of the oilfield production enhancement operation equipment and a variety of other support equipment, and can realize automatic pressure adjustment, automatic displacement distribution, and automatic health detection, which effectively improves the operation efficiency of the whole system.
Offshore low-permeability oil and gas field reserves are an important source of potential reserves for China’s offshore oil production. For a long time, offshore oilfield fracturing technology has been monopolized by a few European and American countries and strictly blocked to our country. Due to the lack of specialized technology and equipment, it is out of our reach. In order to solve this “neck-breaking” problem, SDARI gave full play to its rich experience and R&D strength accumulated in the field of marine engineering, has started from scratch, and finally succeeded in researching and developing the world’s largest and China’s first well stimulation vessel.