Hydraulic fracturing of oil reservoirs is one of the main measures for increasing injection in oil and water wells, and fracturing equipment plays an important role in the fracturing effect. Fracturing equipment mainly includes fracturing truck, blender truck,
High-Pressure Manifold
truck, sand truck, instrumentation truck and related equipment.
1. Requirements of Downhole Operations for Fracturing Equipment
The function of fracturing equipment is to use a fracturing truck to increase the pressure of fracturing fluid and pump it into the formation, creating new fractures or extending original fractures in the producing zone at the bottom of the well. The blender truck mixes proppant with fracturing fluid in a certain ratio and supplies it to the fracturing truck, so that sand-carrying fluid enters the formation, fills the opened fractures, forms a high-permeability zone, and increases oil-well production and water-injection-well injection rate.
According to its function, fracturing equipment should meet the following requirements.
1. Certain Pressure and Displacement
Oil reservoirs are buried in rock formations hundreds to thousands of meters underground. The deeper the reservoir, the higher the pressure. In addition, different rocks have different densities, so pressure also differs. Therefore, fracturing equipment must have enough pressure to fracture the oil zone and must reach a certain displacement, because the larger the displacement, the larger the fracture radius.
2. Continuous and Reliable Working Performance
Fracturing is not an instantaneous operation. Fracturing of a shallow well generally takes dozens of minutes, while fracturing of a deep well takes several hours. Therefore, fracturing equipment works continuously under high pressure and large displacement. If the fracturing equipment fails, the fracturing operation will fail, so the equipment must have high continuous reliability.
3. Good Wear Resistance and Corrosion Resistance of Main Equipment
The blender pump of the blender truck, the fracturing pump of the fracturing truck and related equipment work with sand-bearing and acid-bearing fluids. Sand wears parts and acid corrodes parts. Therefore, related parts of this equipment must have good wear resistance and corrosion resistance to meet the needs of different fracturing operations.
4. Good Off-Road Performance
Fracturing operations are carried out at the well site, where formal road surfaces are usually unavailable. Therefore, fracturing equipment must have good off-road performance to adapt to driving on different road surfaces.
2. Fracturing Truck
The fracturing truck is the main equipment for reservoir fracturing. It mainly consists of carrier truck, deck engine, gearbox, fracturing pump, operating console and High-Pressure Manifold.
1. YLC-1000 Fracturing Truck
The YLC-1000 fracturing truck was designed by Yumen Oilfield Research Institute and is commonly called the thousand-type fracturing truck. This fracturing truck has three models: A, B and D. Its features are high pressure, large displacement, long stroke, simple structure, and convenient operation and use.
1) Transmission
The transmission box of the YLC-1000D fracturing truck is a three-shaft four-speed cylindrical helical gear structure with hydraulic shifting and oil-spray lubrication. Its features include a bidirectional-cylinder structure using hydraulic plate friction clutches; reversing through an electromagnetic lubrication valve; and constant-mesh gears from the gearbox to the planetary reduction gearbox. Shifting has no impact noise and can also be remotely operated. Speeds and transmission routes for each gear are as follows:
Gear I: lower clutch engaged right, upper clutch engaged right, through gears 8-7-6-5 and the planetary reduction gearbox to the fracturing pump. Transmission ratio 2.083, output shaft speed 535 r/min.
Gear II: lower clutch engaged right, upper clutch engaged left, through gears 8-7-3-4 and the planetary reduction gearbox to the fracturing pump. Transmission ratio 2.033, output shaft speed 738 r/min.
Gear III: lower clutch engaged left, upper clutch engaged right, through gears 1-2-6-5 and the planetary reduction gearbox to the fracturing pump. Transmission ratio 1.509, output shaft speed 996 r/min.
Gear IV: lower clutch engaged left, upper clutch engaged left, through gears 1-2-3-4 and the planetary reduction gearbox to the fracturing pump. Transmission ratio 1.039, output shaft speed 1372 r/min.
2) Fracturing pump
The fracturing pump is a three-cylinder single-acting horizontal plunger pump. Compared with ordinary plunger pumps, it has the following features:
(1) The crankshaft is integrally cast and uses a four-support structure, providing stable support and light weight.
(2) The connecting rod uses sliding bearings.
(3) The crankshaft center is 50 mm lower than the crosshead center, so the upper and lower crosshead guideways wear evenly.
(4) The plunger and crosshead are connected by a spring rod, making centering easy and preventing eccentric plunger wear and binding.
(5) High-pressure self-sealing Y-type seals are used between pump head and horizontal and vertical cylinder-cover seal seats, with simple structure and reliable sealing.
(6) The suction valve spring is fixed by the horizontal cylinder-cover seal seat, with simple structure and convenient machining and use.
(7) Packing and valve rubber use polyurethane rubber, which has high strength, good wear resistance, good oil resistance and high compression resistance, extending service life.
(8) A planetary reduction gearbox is used outside the pump. Power enters through the sun gear and outputs through the frame. The planetary gears use rolling bearings, simplifying the structure.
The working principle of the fracturing pump is the same as that of a reciprocating pump.
In recent years, a new hydraulic booster pump structure with long stroke and low stroke frequency has appeared. The working principle is that a large-diameter piston drives a small-diameter plunger. The large piston is driven by high-pressure fluid discharged from a normal fracturing truck, and the intake and discharge sequence of the power fluid is controlled by a control valve. Maximum pump pressure can reach 155 MPa, stroke is 1.534 m, pressure fluctuation is small, and it can pump fluid with a very high sand ratio, making it suitable for deep and ultra-deep well fracturing.
2. Technical Specifications of Common Fracturing Trucks
3. Blender Truck
The function of the blender truck is to draw fracturing fluid from the fracturing tank into the blender tank, convey proppant into the blender tank, stir and mix it, supply the blended fluid to the fracturing truck, assist additive supply, and cooperate with the fracturing truck during operation.
1. Structure of Blender Truck
The blender truck mainly consists of carrier truck, deck engine or carrier-truck engine, transmission gearbox, fluid-supply system, sand conveying device, mixing system, discharge system, operating control system and auxiliary system.
The carrier truck uses a high-performance, high-power heavy truck, such as Huanghe or Mercedes-Benz, with large carrying capacity and strong off-road capability.
The deck engine is the main power source for fluid supply, sand conveying, mixing and discharge systems. Its power must be greater than the sum of the powers required by all working machines. Older blender trucks used gasoline engines with low power and low sand ratio. Current blender trucks mostly use high-power diesel engines, such as the OM403 diesel engine on the SHC60B blender truck with 235 kW power, or use the same engine for both driving and deck operation, such as the HSC-300 blender truck with a Cummins KTA-1150C-600 engine, 448 kW operating power and 224 kW driving power.
The fluid-supply system draws fracturing fluid from the fracturing tank and supplies it to the mixing tank. It mainly consists of hoses, suction pipes and centrifugal pumps.
The sand-conveying system conveys proppant into the mixing tank. Its main components are sand inlet hopper, sand-conveying barrel, screw conveyor and metering device.
The mixing system mixes incoming fracturing fluid and proppant uniformly in a certain ratio, then supplies the sand-carrying fluid to each fracturing truck through the sand pump. It mainly consists of mixing tank, sand pump and discharge pipe.
The operating system controls each mechanism according to commands.
The auxiliary system mainly handles input of various additives.
In an air-suction blender truck, mechanical screw sand conveying is changed to air-suction sand conveying. Its principle is to use the suction action of a blower to create a certain vacuum in the pipeline. When air velocity exceeds the settling velocity of sand, the sand is lifted and carried by the airflow through the suction pipe into the blender tank. Power is supplied by the deck engine, reduced by the gearbox and transmitted to the transfer case. Three output shafts of the transfer case simultaneously drive the blower, water-supply pump and sand pump, supplying the mixed sand-carrying fluid to the fracturing truck.
2. Technical Specifications of Blender Truck
4. Other Fracturing Equipment
In addition to fracturing trucks and blender trucks, fracturing operations also require other equipment such as balancing truck, sand truck, instrumentation truck and manifold truck.
1. Balancing Truck
The balancing truck injects liquid at a certain pressure into the casing annulus above the packer, balancing part of the differential pressure across the packer, improving packer working conditions, and protecting the packer and casing. It can also be used to handle accidents such as fracturing sand plug, reverse washing or reverse-circulation well killing.
The balancing truck is generally replaced by a cementing truck. A cementing truck model meeting the designed balancing pressure is selected. In current field practice, SNC-300H cementing trucks are used for shallow wells and SNC-400 cementing trucks are used for deep-well fracturing.
2. Sand Truck
The sand truck transports fracturing proppant, such as quartz sand, ceramic proppant, walnut shell and metal balls, and dumps the proppant into the sand inlet hopper of the blender truck to complete sand addition. A sand truck generally uses a heavy truck chassis with a sand tank installed on it and hydraulic-cylinder tipping. Field units include Hino, Tatra, Steyr and Tiema. Technical specifications of the YSC-15 sand truck are as follows:
Carrier truck: Tiema (TM) SC2830/6 x 6-45
Engine power: 220 kW
Engine speed: 2500 r/min
Sand tank capacity: 10 m3
Sand tank tilt angle: 45 degrees
Minimum ground clearance: 970 mm
Lifting time: 23 s
Full-load mass: 2700 kg
3. Instrumentation Truck
The instrumentation truck consists of instruments, displays, computers and related systems for measuring fracturing parameters. It measures pressure, flow rate and cumulative flow during fracturing, measures sand ratio, displays fracturing curves and fracturing dynamics, and calculates various fracturing parameters. It is also equipped with communication equipment to contact fracturing trucks and blender trucks, so it is also called a fracturing command truck. Field units include Chevrolet instrumentation trucks from the United States and Huaxi instrumentation trucks made in Mianyang, Sichuan, China.
4. Manifold Truck
The manifold truck is a vehicle specially used to transport Fracturing Manifold. It is equipped with a hydraulic boom. After arriving at the well site, it lifts the manifold to the ground for connection and fracturing operation. After the job, it lifts the manifold back onto the truck for return. The carrier truck for the manifold truck generally uses the same heavy truck type as the fracturing truck, making maintenance and management easier.
