The Liuhua 11-1 oil field is located in the 29/04 contract block of the Pearl River Mouth Basin in the South China Sea, 220km southeast of Hong Kong, with an average water depth of 305m.
The Liuhua 11-1 oil field is an oil field jointly developed by CNOOC and Amoco Orient Petroleum Company. The Liuhua 11-1 oil field was discovered in January 1987. In March 1993, six years after the discovery of the oil field, the government authorities officially approved the overall development plan of the oil field, and then started the construction of the oil field development project. It was put into operation in May 1995. The company is Amoco.
The Liuhua 11-1 oil field includes three oil-bearing traps, namely Liuhua 11-1, 4-1 and 11-1 East blocks. The Liuhua 11-1 block has a basically proven oil-bearing area of ??36.3km2, geological reserves of 15378×104t, controlled oil-bearing area of ??53.6km2, and geological reserves of 6426×104t. The Liuhua 4-1 block controls an oil-bearing area of ??18.2km2 and a geological reserve of 1753×104t. Liuhua 11-1 East Block controls an oil-bearing area of ??11.3km2 and geological reserves of 458×104t. The proven and controlled oil-bearing area of ??the entire oil field is 83.1km2, with total geological reserves of 24015×104t. It is the largest oil field discovered so far in the South China Sea. The Liuhua 11-1 block currently put into development is only a part of the Liuhua 11-1 oil field.
To develop such a large oil field economically and effectively, we are faced with many technical problems: large water depth, harsh environmental conditions, crude oil with a large specific gravity and high viscosity, and the bottom water of the reservoir is sufficient and shallow. In view of these characteristics, through the joint efforts of Chinese and foreign technical personnel, they pioneered and innovated, used new thinking concepts, and adopted the world's top high and new technologies, creating "three firsts and seven first-class" during the project development process.
The Liuhua 11-1 oil field has a design production life of 12 years and a design life of engineering facilities of 20 years. The approved investment budget was US$653 million, and the actual investment final account was US$622 million, a saving of US$31 million compared with the budget.
1. Engineering Development Plan
Liuhua 11-1 Oilfield adopts a deep-water all-ocean development plan. The entire engineering facility includes 5 parts: semi-submersible floating production system (FPS) South China Sea "Challenge", floating production, storage and offloading unit (FPSO) South China Sea "Victory", single-point mooring system, submarine oil pipeline and Subsea wellhead system (Figure 12-1).
Figure 12-1 Liuhua 11-1 Oilfield Engineering Facility Diagram
II. Design Conditions
(1) Environmental Conditions
a ． In addition to the influence of winter monsoons and strong summer tropical storms (typhoons), the Liuhua 11-1 oilfield operating sea area also has a special sea state - internal wave current, which is also a major factor affecting operations and system selection. During the single well test in 1990, there were several accidents caused by internal wave currents, such as cable breakage, hull collision, and even breakage of buoys or crushing of floating hoses.
b. The environmental parameters of Liuhua 11-1 oil field are shown in Table 12-1.
c. The design parameters of the "Challenge" FPS flexible riser in Liuhua 11-1 Oilfield are shown in Table 12-2.
d． The FPS design environment parameters of the Liuhua 11-1 Oilfield "Challenge" floating production system are shown in Table 12-3.
e. The directional sea state design parameters of the Liuhua 11-1 Oilfield "Shengli" FPSO are shown in Table 12-4.
Table 12-1 Liuhua 11-1 oil field environmental parameters
Table 12-2 "Challenge" FPS flexible riser design parameters (once in a century)
Table 12-3 "Challenge" FPS floating production system environmental design parameters
Table 12-4 "Victory" FPSO directional sea state design parameters
(2) Fluid properties
Liuhua 11-1 oil field is a crude oil with high specific gravity, high viscosity, low sulfur content, low wax content, low freezing point, low dissolved gas-oil ratio, and undersaturated naphthenic biodegradable crude oil.
The main parameters of surface crude oil are:
Relative density: 0.92~0.97;
Viscosity: 50~162mPa.s;
Sulfur content: 0.28~0.41 ;
Wax content: 0.43~6.21;
Freezing point: -12~4.4℃;
Saturation pressure: 0.91MPa;
Original dissolved gas-oil ratio: 1.6~18.9m3/m3.
Other performance indicators of crude oil are shown in Table 12-5.
Table 12-4 Various performance indicators of crude oil from Liuhua 11-1 Oilfield
Continued table
(3) Other design parameters
Underwater wellhead supporting equipment, including pressure instruments, the maximum working pressure of the pipeline is 15.5MPa (22401b/in2);
Peak daily production of a single well: 2384m3/d, water content range 0~93;
FPSO daily processing capacity: 47670m3/d;
Atmospheric temperature: 16.4～33.7℃;
Underwater operating temperature: 11～31℃;
Well fluid temperature: 11～52℃.
All piping materials and metering and pressure instruments should be suitable for conveying liquids with hydrogen sulfide and carbon dioxide. The inner surface should be chemically anti-corrosion treated, and the outer surface should be protected with paint and sacrificial anodes.
(4) Extended Test
In order to solve the problem of rapid coning of strong bottom water in the oil field, slow down the water cone speed, and tap the potential of the oil field to a greater extent, we further analyzed the long-term production capacity of the oil field. To effectively improve the recovery rate, it took half a year to conduct extended testing on three wells before formal development.
a. Well Liuhua 11-1-3 is a vertical well that penetrates the reservoir, with an initial daily production of 363m3 and a comprehensive water content of 20. After 42 days, the daily production is 350m3 and the comprehensive water content rises to 70.
b. Well Liuhua 11-1-5 is a highly inclined extension well. The well inclination section falling into the reservoir section reaches 78. The initial daily production is 1271m3, and the comprehensive water content is 0; after 51 days, the daily production drops to 874m3, and the comprehensive water content rises to 51. The water cone rising speed is significantly improved compared with vertical wells.
c. Well Liuhua 11-1-6 is a horizontal well, and all horizontal well sections fall into the section with the best permeability at the top of the oil layer. The initial daily production is 1907m3, and the comprehensive water content is 0; after 120 days, the daily production is 1017m3, and the comprehensive water content is 26. Compared with the first two wells, the use of horizontal well mining can not only increase the output of a single well, but also slow down the water cone speed of the bottom water, which is the best development plan for the oil field.
3. The "Challenge" Floating Production Platform (FPS) in the South China Sea
The water depth in the Liuhua 11-1 oil field is nearly 310m. It uses a conventional jacket fixed platform structure, with only the catheter The rack itself costs as much as $1 billion, and the cost of building a new tension leg platform is estimated to be $1.2 billion. After technical and economic demonstration and comparison, the plan to modify the semi-submersible drilling platform was finally adopted, and the total modification cost did not exceed US$200 million. According to the usage requirements, the modified floating production system can not only withstand the harsh sea conditions that occur once in a century in the sea area, but also meet the requirements for drilling, completion and workover operations. It can also install, recover and repair underwater wellhead equipment, monitor and control water Go down to the wellhead to provide a suspended moon pool and power supply for the bottom-hole electric submersible pump. According to the directional nature of typhoon extremes, and the extreme values ??of wind, waves, and currents in the northeast are significantly greater than those in the northwest, the conventional symmetrical mooring method of 8 or 12 anchor chains is changed to an asymmetrical 11 anchor chains. According to the actual stress conditions, the length of most anchor chains is shortened. The diameter of the anchor chain is φ127mm and the weight of a single anchor is 40t. It is the largest anchor currently used for commercial purposes at sea. The mooring capacity can withstand the attack of a strong typhoon that occurs once in a century, permanently mooring the South China Sea "Challenge" to the seabed.
The design service life of "Challenge" is 20 years.
In July 1993, a semi-submersible drilling platform for renovation was purchased. After 22 months of renovation design and shipyard construction, it was moored to a predetermined location in the oil field in April 1995.
"Challenge" is also equipped with 2 ROV remote-controlled robots to support operations and provide power to the wellhead through 25 underwater cables. The living module can accommodate 130 people.
4. Floating Production, Storage and Offloading Oil Tanker (FPSO) and Single Point Mooring System
(1) South China Sea "Victory" Floating Production, Storage and Offloading Oil Tanker (FPSO)
p>The "Victory" in the South China Sea was refitted from an old 140,000-ton oil tanker. The tanker is 280m long, 44m wide, 23m deep, and 17m draft. The modified tanker has the functions of power generation, crude oil purification, crude oil storage and oil unloading. The peak daily liquid processing volume is 4.77×104m3, the daily oil production is 1.03×104m3, and it can store 720,000 barrels of crude oil. In view of the viscous characteristics of crude oil in Liuhua 11-1 Oilfield, the crude oil treatment process adopts the world's most advanced two-in-one electric desalination/dehydration technology, which means that crude oil desalination and dehydration are completed step by step in one equipment. This is the first time in the world that this new technology has been used in offshore oil fields. It not only saves a lot of space, but also saves millions of dollars in engineering costs.
The "Victory" living building module can accommodate 85 people. The stored qualified crude oil is transported and sold via shuttle tankers.
(2) "Victory" single-point mooring system
The "Victory" floating production, storage and offloading system (FPSO) adopts a permanent internal turret single-point mooring system. The single point is fixed to the seabed with an anchor chain and is connected to the hull through the turret mechanism in the front cavity of the tanker hull. The tanker can rotate 360° around the single point. This structural form is used for the first time in China and is much more economical than a fixed tower mooring structure in deep water conditions. The design environmental conditions are based on extreme sea conditions encountered once in a century, and 10 Φ114.3mm anchor chains are used for mooring. According to the difference in extreme values ??in each direction of environmental conditions, the length of the anchor chain should be adjusted appropriately. The single-point mooring system is permanently non-detachable and has a maximum mooring force of 600t.
5. Underwater production system
(1) Selection of underwater wellhead system
a. The decentralized underwater wellhead production system is suitable for situations where the sea current distribution along the depth in the operating sea area is basically consistent and relatively stable. Underwater wellheads can be connected through flexible pipelines or connected to the main manifold, or directly connected to tankers. The advantage of this underwater wellhead system is that it already has some experience, and the positioning accuracy of the wellhead and surface casing is low. Its disadvantages are that the cost and installation cost of hoses and special hydraulic joints between underwater wellheads are high. When the sea current direction is unstable, it is easy to cause the hose to become entangled, causing damage to the hose and joint parts. Single well workover will affect other wells. Well production, and construction and installation have high sea conditions and long time requirements.
b. The centralized underwater wellhead production system is suitable for various ocean current conditions. The wellhead guide bases are connected as a whole by steel jumpers. This structural form has never been used before. There is a lack of experience and ready-made supporting technology and equipment, and the positioning accuracy of the wellhead and surface casing is required to be high. On the other hand, the advantage of this structural form is that the cost of steel jumper joints is much lower than that of flexible hoses and hydraulic joints, only about 1/3 of the latter. The workover operation of a single well does not affect the normal production of other wells. Relatively independent hoses can be installed and recovered independently, and the range of movement is small, and friction and entanglement of the hoses will not occur. The measurement, installation and recovery operations of steel jumper pipes can be It can be carried out simultaneously with other operations and does not require the use of other ships. It can operate as usual in rough sea conditions and is highly efficient. After comprehensive research and comparison, the centralized underwater wellhead production system was finally selected.
(2) The main structure and reassembly sequence of the underwater wellhead system
The centralized underwater wellhead production system is called the "block overlapping control system" and is Liuhua 11 -1 The most innovative system in oilfield engineering. The first new technologies include: central manifold; steel inter-wellhead jumper; application of wet electrical joints on offshore platforms; catenary flexible riser system supported by floating production platforms ; Underwater production hydraulic control system; remote-controlled underwater operating robot ROV; new submarine pipeline fixed base and steel long jumper pipe; underwater horizontal Christmas tree.
The underwater wellhead equipment is installed in three parts. First, lock the production guide base (PGFB) on the 762mm surface casing head, and use steel jumpers to connect the lower gathering and transportation pipeline joints of the PGFB. , thereby connecting the independent underwater wellheads to form a double-line closed loop, then locking the underwater tree on the 476mm wellhead, connecting the oil flow line joint of the tree to the valve on the production base, and finally The Christmas tree cap and the electric submersible pump cable are covered on the Christmas tree. The circuit of the electric submersible pump is connected. The crude oil enters the lower gathering manifold of the PCFB through the tree outlet, collects into the central manifold, and then passes through the central manifold. The long steel jumper pipe enters the submarine oil pipeline and is transported to the South China Sea Challenger for processing.
(3) Functions of underwater wellhead equipment
1. Central manifold
The central manifold block is 21.3m long, 2.1m wide, 2.1m high and weighs 60t. It consists of two 457.2mm production pipelines and one 203.2mm test pipeline, corresponding to two 342.9mm (13.5in) subsea oil pipelines and one 152.4mm subsea test pipeline respectively. Each pipeline introduces 6 joints, 4 of which are connected to the 4 wing valves of the wellhead Christmas tree, 1 joint is connected to the subsea pipeline, and 1 joint is used as a switching valve between pipelines. During installation, use a platform crane to lift and straighten the central manifold, approach the turntable, and then use a drilling rig hook to pass through the moon pool and place it on the seabed. The central manifold also serves as the basis of the hydraulic panel, and the hydraulic signals from the main control room are transmitted to each production tree through the distribution panel.
2． Permanent production guide base PGFB
Compared with conventional permanent guide bases, in addition to being larger in size at 4.8m×4.8m, it not only has the function of guiding and making foundation, but also has the function of collecting liquid. Two 304.8mm liquid collecting pipes are designed at the lower part of the base. The crude oil from the Christmas tree enters the liquid collecting pipe through the production valve. The guide rod of the base has also been improved and can be recycled multiple times.
3． Horizontal underwater tree
In order to adapt to underwater operations without manual diving, this kind of tree cap is designed with all valves in the horizontal direction and operated by underwater robots. The switches of 16 ball valves with different performances are concentrated on an operating panel that is convenient for remote control robot ROV operation. The robot can operate these switches to control production valves, annulus valves, safety valves, chemical injection valves, etc. These valves can also be opened and closed under platform hydraulic control, and the safety valve can be automatically closed in an emergency.
4. Underwater Christmas tree cap
The Christmas tree cap covers the top of the Christmas tree. The wet electrical connector (WMEC) socket is fixed on the inside of the cap, and the dry electrical connector (DMEC) plug is inside the outer flange. The connector is fixed in the IWPC terminal flange, and the dry electrical connector flange is first connected on the platform. Considering that harsh environmental conditions may pull the IWPC and cause damage to the Christmas tree, a safety breaking flange is designed at one end of the IWPC. Before the load reaches the point of damaging the Christmas tree, the bolts of the breaking flange break first, making the IWPC and the Christmas tree The cap comes off.
5． Installation of Christmas tree and Christmas tree cap
The tool used in the installation operation is a multi-functional completion and workover tool (URT). This tool sits on the Christmas tree through four guide cables. The entire system is controlled by hydraulic pressure. It can automatically center and adjust the height smoothly and efficiently. It can not only install the Christmas tree and the Christmas tree cap, but also recover the Christmas tree cap. Temporarily It is parked on the PGFB to conduct tubing plug sealing pressure and wet electrical joint circuit testing, eliminating the complicated task of taking the tree cap and IWPC back to the platform for testing and then installation.
The lower part of this tool is a rectangular frame structure. The distance between the four funnel cylinders used as guides is exactly the same as that of the Christmas tree guide funnel. A central rod can move smoothly through hydraulic control.
6. Underwater Remotely Operated Robot (ROV)
The two robots are designed and manufactured according to the usage requirements of Liuhua 11-1 Oilfield. One is permanent and operates on the platform; the other is mobile. Can be moved to a work boat for diving operations. Both robots have a power of 73.5kW (100HP), 6 propellers, and 6 cameras (one of which is adjustable focus, and one is a pen type mounted on the manipulator), and can be towed in 2 miles of sea currents. The 183m umbilical cord operation is equipped with a multi-functional module - MFPT. The ROV is equipped with the following modules: rotating tool module, manipulator plug-in hydraulic thruster, automatic centering telescopic hydraulic drive, auxiliary work tools, flexible working rope cutter, cable cutter, cable grasper, low-pressure flushing gun, butter injection tool, Positioning telescopic suction cup, hydraulic circular saw, a 7-function Schilling manipulator, a 5-function Schilling powerful manipulator and pin extraction function, etc. Since the requirements of various operating conditions were taken into consideration during the design and model tests were conducted in advance, the performance was good during the actual operation and the operating efficiency has been maintained at a very high level.
7. Subsea pipeline connection fixed base (TIB)
Submarine pipeline connection fixed base (TIB) is a device that connects subsea pipelines and underwater wellheads. One side of it is connected to the subsea wellhead central manifold through three long steel connecting pipes with lengths of 22.9m, 17.4m and 11.3m, and the other side is connected to three subsea pipelines. The subsea pipeline connection fixed base (TIB) is installed on the floating production platform, and the connection between the TIB and the three subsea pipelines is completed by a submersible hose connection system (DFCS). The DFCS is carried into the water by one ROV. When the submarine pipeline is lowered to the target position, another ROV will lead a wire rope from the DFCS, hang the QOV shackle at the end of the wire rope on the hanging point of the submarine pipeline connector, and tighten the wire rope , make the submarine pipe interface follow the guide trough and gradually get close to the interface on the TIB. The ROV inserts the hydraulic driver plug into the joint locking hole to lock the joint. After passing the sealing and pressure test, loosen the ROV shackle on the joint to complete the installation operation. .
6. Submarine oil pipeline
The Liuhua 11-1 oil field submarine pipeline consists of three parts.
1． Production pipeline
Quantity: 2;
Diameter: 131/2”;
Transmission medium: oil-water mixed liquid;
Material : Power flexible hose;
Distance: from the subsea pipeline riser base under the "Challenge" floating production system (FPS) to the "Victory" floating production, storage and offloading unit. Riser base (PRB);
Length: 2.24km
2. Metering pipeline
Quantity: 1;
Diameter: 6";
Transmission medium: oil-water mixed liquid, single well metering or instead of production pipeline in emergency situations;
Material: power flexible hose;
Distance: from the riser base under the "Challenge" floating production system (FPS) to the riser base (PRB) under the "Victory" floating production, storage and offloading unit;
Length: 2.24km.
3. Riser
Quantity: 2 production risers, 1 metering riser;
Diameter: 131/2" production riser, 6" metering riser;
Transmission medium: liquid;
Material: Power flexible hose;
Distance: from the riser base under the "Victory" floating production storage and offloading device Go to the turret single point above.
7. Horizontal well drilling technology
(1) Wellbore trajectory design
The oil field is characterized by a large area and shallow oil reservoir burial depth. The vertical distance to the top surface of the reservoir is only 914m.
Limited by the depth of the reservoir, the maximum control radius of horizontal well drilling on the platform is approximately 3km. In order to ensure that the electric submersible pump can operate without lateral torque, the horizontal wellbore trajectory is designed to be divided into two inclined well sections, and a stable inclination section is designed between the two inclined well sections, and the electric submersible pump is Run into the stable inclined well section. In order to prevent the electric submersible pump from being damaged when it is run in, the deflection rate of the first deflection well section shall not exceed 7°/30m. The designed horizontal well sections of the 20 horizontal wells are all located in the B1 layer with a thickness of about 6.8m and the best porosity. The length of the horizontal section is 800m, and the total horizontal displacement is about 910-2590m.
(2) Drilling technology and characteristics
a. First, the new process of casing while drilling was used to install casing, and the installation of 25 pipes was successfully completed. The total installation operation time is 14.4 days, and the average single well installation time is 14.8 hours. Compared with the conventional method, the time saving is 36 days.
b. The batch drilling method is adopted for the 444.5mm (171/2in) and 311.2mm 215.9mm (121/4in 81/2in) well sections respectively. The measured depth of the 444.5mm well section is 650m, and the average single well completion time is 1.5d; the measured depth of the 311.2mm 215.9mm well section is 2040~3048m, and the average single well completion time is 10.8d. The application of batch drilling operation method greatly speeds up the drilling operation.
c. The drilling fluid uses a PHPA water-based mud system and seawater (plus Xanvis mud) to drill the inclined section and horizontal section, which reduces mud costs, increases drilling speed, reduces pollution to the oil layer, and protects the environment.
d． Steering drilling technology uses advanced horizontal well design technology and GST (Geosteering Tool) downhole steering drilling tools to keep track of the drilling status and monitor the strata encountered, determine the depth of the target layer in a timely manner and adjust the well trajectory, which not only speeds up the drilling progress, but also makes The proportion of horizontal wells accurately falling into the B1 target layer with a thickness of only 6.8m reached 91%.
(3) Main drilling indicators
Before the oil field was put into production, in addition to installing 25 sets of 762mm (30in) conduits in batches, 17 wells were drilled and 12 wells were completed. , the total footage was 28207m, the total days were 180d, the average measured well depth was 2351m, the horizontal well section was 813m, the proportion of horizontal well sections entering the B1 target layer was 91, the single well operation cycle was 13 days, and the single well cost was US$1.96 million.
8. Completion string
1. Tubing hanger
The installation of the completion string is completed by lifting and lowering the tubing hanger with the tubing hanger installation tool (THRT). The oil pipe is hung through the guide groove and guided to the landing, and then locked in the sealing cloth core in the Christmas tree.
2. Wet Electrical Connector (WMEC)
Wet Electrical Connector (WMEC) is the terminal of the electric submersible pump downhole cable. Foreign standardized products are selected through bidding. The plug is fixed in the tubing hanger and the socket is fixed in the Christmas tree cap. , when the tree cap is covered, the sleeve-shaped socket is put on the oil pipe hanging plug together with the tree cap, and it can be powered by docking in sea water, and it is guaranteed not to leak electricity, and no special installation is required. The engaging part of the plug is similar to an ordinary three-phase plug. The entire sleeve socket is about 50cm long and 8cm in diameter.
For insurance purposes, use electrical insulating fluid to flush the space between the tree cap and the tubing hanger, and then use nitrogen to squeeze out the electrical insulating fluid to ensure that the wet electrical connector (WMEC) will not deteriorate over a long period of time. Under the working conditions of variable high voltage and variable frequency high current, the work generates high heat, which causes thermal expansion of the tree cap and damage it.
The working parameters of the wet electrical connector are: voltage 5kV, current 125A, frequency 60Hz.
3. Electric submersible pump
Due to the characteristics of high viscosity, high density, low bottom hole pressure and rapid rise in water content of the crude oil in Liuhua 11-1 Oilfield, the electric submersible pump oil production technology was selected. The electric submersible pump selected is the 562 series electric submersible pump assembly provided by Reda Company, HN13500, 73Stages, 540HP, 125Ams, 5000Volts.
The lower end of the underwater cable that supplies power to the electric submersible pump is connected to the Christmas tree cap, and the upper end is suspended on the lower deck of the FPS and connected to the frequency converter in the electric submersible pump control room. The opening and closing of single-well production valves and safety valves are directly controlled by the hydraulic system on the FPS. The hydraulic joints on the production tree are connected to the underwater central manifold hydraulic distribution plate through underwater control hoses, and the hydraulic distribution plate is connected to the subsea central manifold through hydraulic control cables. The FPS central control room is connected.
4. Subsea setting production packer
The re-setting packer provided by NODECO has 4 channels, including formation fluid flow channels, ESP cable traversers, chemical injection pipelines and backup Pipeline channel. Its main feature is that it can be set again. The use of a re-set packer can avoid having to pull out the pipe string and replace the packer every time the well is repaired, thus saving the time and cost of the well repair.