The oilfield covers an area of 9.8km2, with proven geological reserves1903x104t approved by the State Reserve Committee, controlled geological reserves of 473x104t and total reserves of 2376x104t.
The oil field was discovered in1May, 986, and the original producer was the American Western Far East Oil Company. 1991September, Australian AMPOLEX Oil Company took over the original business and continued to evaluate Lufeng 22- 1 oilfield. 1995 submitted the master development plan report to the Chinese side in September, and it was approved by the competent authorities in March, 1996. In June of the same year, AMPOLEX officially transferred Lufeng 22- 1 Oilfield to STOTAIL Petroleum Company of Norway. Stotel Oil Company took over the operation right, further evaluated the reservoir, optimized and adjusted the development plan, and finally selected a multifunctional "Muning" floating production storage and unloading tanker FPSO and the underwater wellhead, and connected the development plan of the floating production storage and unloading tanker FPSO through a flexible riser.
Project construction starts from 1996 65438+ 10, and development wells start from199665438+February. From 1997 65438+ 10, the machine was completed, and it was officially put into production from 65438+February 27th, with a peak daily crude oil production of 0.9× 65438.
I. Technical Difficulties in the Development of Lufeng Oilfield
A. the geological conditions are complex. This oilfield is a bottom-water reservoir, and the depth of oil-water interface is1626 m. In order to meet the requirement that the blowout avoidance height is not lower than 10m, the borehole cannot be drilled to the depth of 16 10m, so it is very difficult to control the borehole trajectory. The reservoir is controlled by fault strike segmentation, and the trajectory of horizontal well must follow the main fault strike, which makes the horizontal section of horizontal well have to turn; In addition, the influence of borehole trajectory, especially the existence of deep fault at the kick-off point and fault risk less than 5m, is easy to cause leakage and collapse during drilling.
B the chassis drilling scheme determines the position of the platform, and at the same time affects the trajectory of five horizontal wells, which affects the whole drilling workload and increases the difficulty of drilling operation.
C. The horizontal section of each well requires high accuracy, the allowable deviation is small, and the well trajectory control is difficult, which not only requires accurate measurement technology, but also changes the L-shaped well trajectory, which is easy to form keyway and wear casing, and increases the difficulty of hitting the target.
D. In view of the risk of lost circulation in drilling, it is necessary to comprehensively consider borehole purification and borehole stability, carefully study and select mud types, and determine various hydraulic parameters.
E. It is also a difficult point to prevent buckling during drilling and ensure sliding drilling.
F in addition to completing drilling operations, the drilling platform must also undertake many underwater installation tasks. Therefore, drilling operation has become an important way of oilfield development.
The second is the new technology adopted by Lufeng Oilfield.
This oil field is another large-scale deepwater oil field developed by Sino-foreign cooperation in the South China Sea by using the world's high and new technologies, which has successfully created the mode that China has only one tanker to develop offshore oil fields. To sum up, there are nine new technologies adopted: ① multifunctional floating production storage and unloading tanker FPSO; Combined with standard production module; (2) a foldable suspension combined chassis host; ; (3) Multiphase underwater electrically driven underwater booster pump; (4) A new detachable diving STP single-point mooring system; ⑤ Deep-water suction anchor; ⑥ Underwater dual positioning horizontal oil production wellhead; ⑦ New technology of vertical gravity butt joint installation of riser; ⑧ In the development of all horizontal wells in the oilfield, the horizontal section of a single well over 2000m turns along the fault strike; Pet-name ruby electro-hydraulic remote control submersible operation mode.
Third, the design conditions
1. Environmental parameters (once in a hundred years)
Lufeng 22- 1 Oilfield is located in subtropical zone and affected by monsoon. Frequent typhoons and strong cold currents from Siberia make the sea conditions in this area worse. Internal wave current is a kind of underwater flow, which has extremely adverse effects on the safety and production of marine buildings. The main environmental parameters are as follows:
Maximum astronomical tide:1.58m.
Maximum wave height: 22.8m.
Maximum wave height period: 12.2 seconds
Seawater temperature: ① The maximum surface temperature is 30.42℃; ② The average surface temperature is 24.865438 0℃; ③ The lowest surface temperature is 265438 0.5℃; ④ The lowest bottom temperature is 10.78℃
Sea surface velocity: 2. 1 1m/s
Bottom velocity of seawater: 0.75m/s.
One-minute average wind speed: 50.3m/s.
Maximum temperature: 36℃
Minimum temperature: 7℃
2. Fluid property parameters
Formation crude oil: viscosity is 4.35mPa.s
The gas-oil ratio is 0.7m3/m3.
Degassed crude oil: the relative density is 0.856.
Pour point 43 ~ 46℃
The viscosity was 22.8 MPa sec.
Freezing point 42.2℃
The wax content is 25.46%
The content of colloidal asphalt is 5.0%
Sulfur content 0.07%
Oilfield water: water type CaC 12
The total salinity is 28,252 mg/L.
Chloride ion 16927 mg/l
Four. Oilfield development plan
Lufeng Oilfield has a water depth of 333 meters, harsh sea conditions, complicated geological conditions, low gas-oil ratio, low pressure, high water content and high wax content in the early stage, so it is very difficult to develop the oilfield. China Offshore Oil Corporation and Norwegian National Petroleum Corporation applied high and new technologies to transform oil fields with no commercial exploitation value into oil fields with exploitation value. After careful economic evaluation and technical research, they finally decided to adopt the new technology of offshore oil development in recent years and adopt an engineering development scheme with feasible technology, simple equipment and low cost: only 1 multifunctional floating production tanker is used to cooperate with underwater wellhead scheme. The oil flow is directly transported to the multifunctional floating production tanker for treatment through the underwater wellhead, and then transported by the shuttle tanker.
It is completely different from the previous conventional oilfield development methods, such as building platforms, setting up single points, laying submarine pipelines, mooring floating production facilities and so on. Lufeng 22- 1 Oilfield only rents 1 Newly built multifunctional floating production tanker. After the operation of Lufeng 22- 1 Oilfield for 2-7 years, it can also serve other oilfields, which will greatly reduce the upfront capital investment and the overall project development cost of the oilfield. It is estimated that this development method reduces at least half of the investment in oilfield development equipment.
Lufeng 22- 1 Oilfield development engineering facilities mainly include (Figure 12-2): 5 horizontal wells; Underwater suspension combined wellhead chassis host; ; Multi-phase electrically driven underwater booster pump for artificial lifting: multi-functional floating production tanker "Muning" with production module; Production mooring system of detachable underwater turntable; Multi-channel rotary joint with four functions (liquid production, high voltage electricity, low voltage signal and hydraulic pressure).
(1) Underwater wellhead
There are 5 horizontal wells in Lufeng 22- 1 Oilfield, and the length of horizontal wells is 470 ~ 2060 m.. The wellhead and Christmas tree of horizontal well are located on the articulated combined chassis. The liquid from the production well flows through the Christmas tree, is transported to the production manifold on the chassis, and then enters two 203.2 mm (8 inches) flexible production risers, which are connected to the floating production storage device.
Figure 12-2 Lufeng 22- 1 Oilfield Engineering Facilities
(2) Floating production oil storage and unloading device
The floating production, storage and unloading tanker "Muning" was transformed from a multifunctional shuttle tanker. The tanker is 253 meters long and 42 meters wide, with double hulls, total deadweight 10.3× 104 tons, and can store crude oil 10.2× 104 tons (640,000 barrels). The processing equipment is installed behind the main deck, and the designed daily processing capacity of crude oil is1.9×1.04m3 (1.25 million barrels) of oil-water mixture; The main engine room, living quarters and helicopter deck are located at the bow, and all oil tanks can be heated by steam. Cargo oil, ballast pump house and electric propeller engine room are also located at the bow. The ship adopts diesel electric propeller and dynamic positioning system, which can keep the ship in the predetermined position without using anchor. The central control room (CCR) can monitor the main equipment on board and the implementation of underwater production. The living area can accommodate 86 people. Three free-falling lifeboats were also installed on board.
Because of the high wax content in crude oil, the production and processing equipment must keep the temperature of crude oil above 62℃. The standard design of water content of qualified crude oil in tanks is 0.3%, and the separated produced water is treated until the oil content is lower than 50× 10-6, which meets the environmental protection discharge standard before being discharged into the sea.
When a strong typhoon comes, the offshore personnel need to evacuate the site, and the floating production storage and unloading device "Mu Ning" can be quickly released from the underwater turret production mooring system.
(3) Production mooring system (STP) of underwater turntable
The production mooring system of underwater turntable mainly includes two parts.
(1)STP buoy and mooring system
The mooring of "Muning" is fixed on the sunken buoy with six suction anchors, which can be moored on the floating production storage and unloading tanker or released when the wave height is 7m. After being released, the STP buoy sank about 45 meters underwater. The suction anchor designed by Norwegian APL Company and Tianjin Neptune Engineering Technology Co., Ltd. has a diameter of 5m, a height of 10m, a single anchor weight of 45t and a designed mooring force of 680t.
(2)STP rotary joint (STP-RC)
STP-RC rotary joints include six high-voltage electric rotary joints for supplying power to booster pumps, 1 set of hydraulic rotary joints for supplying hydraulic power and injecting chemicals to underwater devices, and 1 set of control signal rotary joints for transmitting signals between upper facilities and underwater control system. There are also two φ203.2mm crude oil production channels, through which the crude oil produced underwater is transported to Muning.
(4) Underwater suspension wellhead combined chassis host
1. Characteristics of suspended combined chassis
The full name of hanger over substructure template, abbreviated as HOST, is a wellhead chassis developed by Norwegian Kongsberg Offshore a.s (abbreviated as KOS) Offshore Engineering Company in recent two years. At present, Lufeng 22- 1 Oilfield adopts the second set in the world, which is the first time that China's offshore oil and gas fields adopt the main engine system wellhead. The main features of the host system are as follows.
(1) has flexible design and strong adaptability.
Aiming at the shortcomings of the traditional integral chassis in the process of manufacturing, transportation, installation and production, the main engine system divides the integral chassis into a central module and several wellhead guiding modules. The number and size of steering modules depend on the scale of oil field and the number of wells, which has strong adaptability.
(2) simple structure and convenient operation
After the central module is fixed, assemble the wellhead guide modules one by one around the central module, and then install the wellhead for drilling and the Christmas tree for completion on the guide modules in turn through the guide columns according to the operation procedures. All installation operations can be realized by conventional drilling platforms.
(3) light and flexible, easy to transport
The main engine chassis can be divided into several small modules, which are specially designed for the 6.5m×5.5m moon pool of the conventional semi-submersible drilling platform. Therefore, it can be transported to the bottom of the platform moon pool by barge, hoisted to the moon pool by crane, towed to the destination by platform and lowered to the well site. The central module of LF 22- 1 oilfield main engine system has a size of 5.95m× 5.45m×1.777m and a weight of 30 tons.
(4) steel is saved, and the installation cost is low.
Compared with the conventional integral chassis with the same number of wells, it can save 25% steel and 40% installation cost.
(5) Meet the completion requirements.
The completion system used in the main wellhead meets the requirements of conventional completion. The wellhead system adopts uwd-5103.3mpa (150001b/in2) series, and the tubing hanger adopts the conventional 127mm×50.8mm(5in×2in) system. 177.8 mm (7 inches) tubing hanger and horizontal Christmas tree are the characteristics of the host system.
2.2 installation technology. host system
A. Before towing the drilling platform, hoist the main engine to the drilling platform.
B. After the drilling platform and the main engine center module are towed to the oil field well site, firstly, the seabed obstacles are investigated, the inspection range is 40m, and the seabed gradient is lower than 1.0. At the same time, the guide ropes, pneumatic winches and recovered guide rope joints in the moon pool area are inspected.
C. After positioning and ballasting the drilling platform, start drilling the center hole of 1066.8mm(42in), with the designed hole depth of 394m and the measured well deviation α less than or equal to 0.5. Before tripping out, replace 20m3 high viscosity mud. Use ROV to install sensors about 4m away from the borehole, and install three buoys with 2m long ropes before and after 6m to check the installation height of the central module.
D. running the central module:
Connect the 9 14.4mm central conductor string with conventional casing running method, and connect the 762mm(30in) conductor wellhead running tool and cementing string, and mark them properly.
Cutting the fixed welding points between the center module and the steel beam, and between the steel beam and the left and right sides of the moon pool; Lower the catheter string, sit on the main engine center module on the moon pool, lock the locking module of the center module, clamp the center catheter, push out the lower locking module to clamp the center catheter, and confirm that it is in a locked state.
Insert the guide head of the guide rope into the guide post corresponding to the corner of the central module and lock it, lift the central module and remove the steel cushion beam under the module; Inject seawater into the central conduit and close the valve on the feeding tool; Lower the central module above the seabed, and keep the guide rope in a straight state during lowering. When the central conductor is 3 ~ 5m away from the seabed, use ROV to find the buoy and aim it at 1066.8mm downhole conductor shoe. Continue to lower the central module to a distance of 2 meters from the seabed, and the maximum distance from the upper surface of the central module to the seabed should be controlled within 3.5 meters: the levelness of the central module is controlled by adjusting the tightness of four guide ropes, so that its inclination is less than 2.
Cementing with conventional methods, after injecting mud, keeping the central module still until the cement hardens; Check and adjust the levelness of the center module to be equal to or less than 0. 10, and the maximum value is 0.3.
Use ROV to insert the rope end of 1 guide rope into the connector of the balance instrument and fix it, and pull the level instrument out of the central module and lift it out of the water; Rerun the guide rope and insert it into the corresponding guide post of the next guide module (HOGS).
E. Install wellhead guide module (pig):
The wellhead steering module (HingOverStructure) is a special mechanism. The central module is connected with the wellhead, which plays the role of supporting and suspending the wellhead and lowering the conduit into the borehole. The HOGS module is also equipped with a drilling rig.
Use the ROV to check whether the rotatable guide column connector of the center module is in working condition, and confirm the position of the locking bolt.
Assemble the running tool into the cart with the crane behind the moon pool, then hoist it behind the moon pool at the tail of the platform, and then connect the lifting ring coming down from the drilling floor to the lifting ring of the running tool. The driller and crane driver work together to send the pig to the moon pool operation area.
Connect the guide rope, lower the pig with the drill pipe, and the running tool makes the pig sit in the correct position of the central module with the help of the guide column.
Use ROV to lock the make-up module and the central module for connection and fixation.
The drilling rig is shifted, and then the corresponding guide column on the central module is connected to install the next pig.
F. Install the permanent guide frame (FGB) of the drilling wellhead;
9 14.4 mm drilling to 4 19 m.
Lift the bushing on the pig with ROVXX, and move the guide frame FGB to the middle of the moon pool with the winch behind the moon pool.
Move FGB to the bottom of the rotary table of the drilling rig by lifting a big bucket, connect the 762mm conduit, lower it to the moon pool with a drill pipe, and then lower the conduit and FGB.
Insert the catheter shoe into the corresponding block, place FGB on the block, and adjust the levelness to less than 0.5; Cementing with water injection mud and checking the levelness of FGB.
G. installing the central manifold
Install a pair of diagonal guide rods on the corresponding diagonal guide columns of the central module and lock the guide column pins.
Lift the central manifold module to the moon pool BOP truck and fix it.
Send the central module manifold to the operation area below the moon pool, connect the wire rope for lifting the central module with the drill pipe joint, lift the drill pipe and lift the central module manifold.
Lower the guide rope to the underwater center module through a pair of diagonal guide columns of the center manifold module and connect it to the pre-installed guide rod; Lower the center manifold module and sit on the chassis of the center module for fixing.
H The installation time of the central module host system is only 3.35d, that is, 4.15d; 7.5d ahead of schedule: the installation time of central manifold module is 38h, which is 22h ahead of schedule of 60h. After the installation of the central manifold module is completed, the horizontal Christmas tree is installed, and the installation time of five Christmas trees is 293h h.