In order to scientifically evaluate oilfield development, reduce the risk of offshore oilfield development, and avoid the mistakes and economic losses caused by the lack of test data in the overall development plan and engineering design plan, it is necessary to carry out extended testing before formulating the offshore oilfield development plan and engineering plan, further verify the reservoir model, calculate the actual productivity of the oilfield, understand the rising trend of water (gas), master the physical and fluid properties of the reservoir, and determine the dynamic characteristics of the reservoir, the best production mode and the applicable oil recovery technology. Considering the exploitation of marginal oil fields and scattered oil wells, it is put on the agenda to build a multifunctional, easy-to-operate, flexible, detachable and reusable offshore extension test and early trial production system (figure 1 1-2).
Figure 1 1- 1 General plan diagram of "I" system for extended test and early trial production.
Fig.11-2 schematic diagram of "Ⅱ" scale-up test and early trial production system.
First, expand the main process of the test system.
The ground process facilities of the extended test and early trial production system depend on the pressure and output of the test well, and generally two-stage separation technology is adopted. Due to continuous testing, the produced crude oil is transported to the tanker, so it is equipped with an external oil pump, a safety fire prevention system and a safety alarm system. See figure 1 1-3 for the ground process flow of the expansion test and early trial production system.
Figure 1 1-3 extended test flow chart
Extended testing and early trial production systems have been successfully applied in Bohai Bay and Pearl River Mouth Basin. The system was granted the invention patent right by the people of China and the national intellectual property rights of China on April 4th, 2000 1 year/kloc-0.
Second, the application of new technology in the expanded test and early trial production system.
(1) The extension test optimized the main parameters of the overall development plan of Jinzhou 9-3 Oilfield.
Jinzhou 9-3 Oilfield, located in Liaodong Bay of Bohai Sea, is a medium-sized heavy oil oilfield discovered by 199 1 1. The overall development plan of the oilfield was completed in June, and was approved by the competent government department in June of the following year. The total number of wells in the scheme design is 68, and an artificial island and two platforms are built. In the stable production period, the annual oil production of the oilfield is 8 1× 104 m3, and the cumulative oil production is 604× 104m3 in five years after exploitation. Because there are too many development wells and platforms designed, the project foundation design investment is large, and the economic evaluation result is poor, so the scheme cannot be implemented.
In order to re-evaluate, three-dimensional seismic acquisition and fine interpretation were carried out in the main part of the oilfield 1992- 1995, and two evaluation wells in Jinzhou 9-3-7 and 9-3-8D were drilled, especially the expansion test and early production test in Jinzhou 9-3-8D 109 days, and more accurate reservoir parameters were obtained. Based on this, the development plan was optimized and revised again, so that the oilfield development reached the profit standard stipulated by CNOOC China. After being shelved for 8 years, the oilfield officially began to develop at the end of 1997.
1. Select the testing system according to the marine environment where the oilfield is located and the requirements of extended testing.
The water depth of Jinzhou 9-3 Oilfield is 6.5 ~10.5m, and the average sea level is 2.03m. The purpose of extension test of Jinzhou 9-3-8D well is to compare the DST results of exploration wells and evaluation wells and find out the relationship between DST and e DST. The selected extension test and early trial production system is jack-up drilling platform+two-point mooring+storage tanker+shuttle tanker.
Jack-up drilling platform has been transformed into a comprehensive operation platform for drilling, extension testing and early production. The crude oil produced during the extended test period is transported to the oil storage tanker through a flexible 3 "floating thermal insulation hose with certain strength, and then transported by the shuttle tanker, which is docked with the oil storage tanker in berthing mode. In order to facilitate floating hose oil transportation and shuttle tanker berthing, the oil storage tanker adopts underwater buoy two-point mooring system.
2. New technologies adopted in extended testing and early trial production system.
The new technologies used in this system are: two-point mooring system of underwater buoy; Double-tube suction anchor; Two tankers use a two-point mooring system for berthing and transporting oil at sea; Floating hose is used for offshore expansion test, etc.
(1) Two-point mooring system of underwater buoy
The system is used to moor oil storage tankers and conduct oil storage operations at sea for a long time. Its mooring system includes: friction chain and nylon mooring cable on the water part, buoy, mooring chain and cement anchor (negative pressure gravity anchor) on the underwater part. See figure 1 1-4.
The system has the characteristics of simple structure, convenient manufacture, installation and use, safety and reliability, simple operation, reusability, less investment, quick effect and good weather resistance. This technology was granted the patent right of "utility model" by the Patent Office of the People's Republic of China on October 23rd, 1999.
(2) Double-tube suction anchor
According to the characteristics of shallow seawater, soft and hard topsoil in the sea area where Well Jinzhou 9-3-8D is located, the fast shear strength is 4 ~ 8kpa within 3m below the mud surface and 6 ~ 20kpa within 3m ~ 6m, the inner cylinder suction anchor is adopted.
When installing the suction anchor, two new technical measures were adopted, namely, remote control integrated pumping and water injection pump, valve system and real-time monitoring system of anchor sinking state, which ensured the smooth construction operation (Figure 1 1-5).
This technology was patented as a "utility model".
(3) Two oil tankers use a two-point mooring system to berth and transport oil at sea.
The crude oil produced during the offshore extension test and early trial production shall be transported to the storage tanker, and the shuttle tanker shall be docked with the storage tanker when the crude oil is exported. When crude oil transportation encounters bad sea conditions and the mooring tension of the tanker exceeds the allowable value, the shuttle tanker must be separated from the storage tanker.
The berthing mode of offshore oil tankers is shown in the above figure 1 1- 1. This technology is the first in China.
Figure 1 1-4 Schematic diagram of underwater buoy type two-point mooring.
Fig. 1 1-5 structural diagram of double-tube suction anchor
(4) The floating hose is used for offshore extension test.
In order to effectively prevent the crude oil produced in the offshore extension test and early trial production from polluting the marine environment, it is necessary to transport the crude oil safely to a nearby oil storage tanker. Because the oil storage tanker is in the irregular change of wind, wave and current, if the rigid submarine pipeline with riser is used for transportation, it can not adapt to the irregular change of mooring oil storage tanker. In addition, the pipeline for transporting crude oil should have certain strength and be easy to release and recover. At present, the flexible floating hose with a resistance of 5t is selected for offshore extension test and early trial production, which is the first time in China.
3. Expand the test results and applications.
From June 23, 1995 to October 9, 1995, Jinzhou 9-3 Oilfield carried out DST test and delayed test for 109 days, including delayed test for 40 days, and accumulated oil production was 15200 tons. At the initial stage of production, the output of a single well was 140m3/d, which was significantly higher than that of Jinzhou 9-3- 1 well and Jinzhou 9-3.2 well, which were the basis of the initial overall development plan. See table 1 1-2.
Table 1 1-2 Comprehensive Productivity Comparison Table of Jinzhou 9-3 Oilfield
The extended test results of Jinzhou 9-3-8D well solved the understanding of oil well productivity, an important parameter in the overall development plan of the oilfield, and made it possible to improve the average single well productivity when compiling the development plan. By adjusting the parameters and re-optimizing the development plan, the predicted daily output index of a single well is about 40m3 higher than the average daily output of the original overall development plan. In the optimized recommended scheme, the total number of development wells is reduced from 68 in the original scheme to 44, and the number of platforms is reduced from 3 to 2. The cumulative oil production in 15 years is 706.9× 104m3, which greatly improves the economic benefits of oilfield development. See table 1 1-3.
Table 1 1-3 Comparison of Main Development Indicators of Jinzhou 9-3 Oilfield
According to the economic evaluation parameters of China Offshore Oil Corporation 1997, the after-tax internal rate of return of the enterprise is 15%, and the total after-tax profit of the oilfield can reach 89 1 100 million yuan after four years of production. The results of sensitivity analysis show that the project has certain anti-risk ability. In June, 1997, 1 1, the drilling operation of oilfield development wells officially started.
(2) The extended test provides an important data basis for the economic and effective development of Liu Hua11Oilfield.
Liu Hua 1 1- 1 Oilfield is located in the Pearl River Mouth Basin of the South China Sea, and it is a reef-beach anticline structural trap. The oil field was discovered in March 1987, and the crude oil belongs to heavy oil with high density and viscosity. The reservoir type is a typical massive bottom water reservoir, and the oil geological reserve of the oilfield is 2.3× 108m3, which is the largest oilfield developed in the Pearl River Mouth Basin of the South China Sea. The water depth of the sea area where the oilfield is located is 3 10m. Frequent typhoons, strong winter winds and unique internal waves and currents in the South China Sea constitute the complex sea conditions in the sea area where the oilfield is located.
1In the first round of comprehensive evaluation in April, 1994, it was assumed that two fixed platforms were used to drill 68 vertical wells for oilfield development. After economic calculation, it is considered that the economic benefit is low, and then two basic production systems are put forward: ① conventional deepwater jacket plus tension leg wellhead platform to drill 60 horizontal wells; ② 30 horizontal wells were drilled by mooring production system of cylindrical floating ship integrated platform. It is estimated that the investment in oilfield development will reach $80 ~ 654.38+0 billion, and its final economic benefit is still not obvious.
In order to reduce investment risk, reduce development cost and seek economic and effective development methods, it is decided to select conventional vertical wells (Liu Hua/KOOC-0//KOOC-0/-3 wells), large-angle deviated wells (Liu Hua/KOOC-0//KOOC-0/-5 wells) and horizontal wells that have been drilled in different reef parts of the oilfield. In order to further deepen the understanding of the reservoir characteristics, reservoir types, fluid properties and oil well productivity of Liu Hua11Oilfield, determine the bottom water activity, the formation conditions and control factors of water cone, determine the initial oil well productivity and its change with water cut, carry out oil field exploitation technology tests, reveal possible contradictions in oil field development, and find effective ways to develop this oilfield.
Semi-submersible drilling platform+mooring system+floating production storage tanker+shuttle tanker is used for extended testing and early production system. See figure 1 1-2 in front of this section for the production system.
1. Main technologies used in extended testing and early production systems.
A. A modified semi-submersible drilling platform, with drilling, completion and workover functions, as well as power generation and distribution equipment required to power the electric submersible pump, and a large-capacity mooring system, ensures that the semi-submersible drilling platform will be permanently moored at the site under extreme weather conditions once in a hundred years.
B. The floating production and storage tanker is transformed from an oil tanker, and has the ability to produce crude oil, treat and store sewage, and install the equipment required for testing. A turret is installed at the bow of the tanker. One end of the anchor chain is tied to the turret of the tanker, and the other end is tied to the submarine gravity anchor.
C output system, that is, shuttle tankers are connected and moored on floating production storage tankers. The oil unloading system includes metering equipment, pipelines, floating hoses, seawater flushing oil unloading pipes, hose lifting system and cable system.
D. adopt gravity anchor mooring system.
2. Extended test result analysis
A. The extension test results show that the productivity of different types of wells is obviously different. Because the thickness of the oil layer drilled by horizontal wells and large-angle inclined wells is 13.5 times and 5.0 times that of conventional vertical wells, it is equivalent to creating a long fracture in the oil layer, expanding the contact surface between the oil well and the oil layer, reducing the seepage resistance near the wellbore and improving the oil well productivity. The average daily oil production of horizontal wells is 2.6 times that of conventional vertical wells.
B the rising speed of horizontal bottom water is much slower than that of conventional vertical wells. Due to the change of bottom water coning mode, horizontal wells and highly deviated wells have changed from point coning to line "ridge" coning. In addition, the production well is long and the oil production intensity per unit length is small, which expands the oil sweeping efficiency. The bottoms of the above two types of wells are far away from the oil-water interface. The results show that the daily growth rate of water cut in horizontal wells is 0.265438 0%, that in highly deviated wells is 0.89%, and that in conventional vertical wells is 65438 0.45%.
C. The controlled reserves of different types of well water flooding are obviously different. According to the calculation results of each well water drive curve, the highest controlled reserve of horizontal well water drive is 93.7× 104m3, followed by large angle inclined well 26.5× 104m3, and that of conventional straight well water drive is only 12.6× 104m3.
3. Main knowledge gained from extended testing.
Due to the natural properties of Liu Hua11oilfield and the unique requirements of high-speed production, it is inevitable that the water cone will be formed in advance, the water cut will increase rapidly, the initial production will decrease rapidly, and the production pressure difference will be large.
B under the advanced oil recovery technology, horizontal wells and large-angle deviated wells can still achieve high oil production at high water cut.
C. Under the condition of large differential pressure production, the vertical relatively dense layer of the reservoir is not enough to effectively block the bottom water coning. The successful test expansion of three different types of wells in Liu Hua11Oilfield provides an important basis for the effective development of this oilfield.
Since the horizontal well can not only increase the single well production and slow down the rising rate of bottom water, but also its drilling cost is only 1.9 times that of the conventional vertical well, the investment and development cost can be reduced by using horizontal well development.
3. Successful application of early production testing system in drilling, production and testing.
Caofeidian 1-6 Oilfield is located in the west of Bohai Bay, which is a buried hill oilfield composed of mixed granite with developed fractures. From1March 1993 to1February 1994, the well Caofeidian 1-6 1 was tested several times to obtain high-yield oil flow. In order to further understand the oil well productivity and verify the oil geological reserves of the oilfield, an early oil testing system (figure 1 1-6) was adopted during the period from 1994 to 165438 10/0, and crude oil/kloc was produced.
Fig. 1 1-6 schematic diagram of supporting engineering of early trial production system for production test while drilling.
This is the first time that the production testing system has been used in exploration wells and evaluation wells in Bohai Sea, and it has been successful in drilling, production and testing. Because of its wide application range, the trial production system can be developed and tested on a large scale in shallow sea areas, and it is completely suitable for trial production of various oil and gas reservoirs in Bohai Sea. It also has the characteristics of simple installation and relocation of equipment and reusability.
(A) the main technological innovation of the system
In order to achieve the purpose of testing while drilling, the function of jack-up cantilever drilling ship was reformed and developed in Caofeidian 1-6 Oilfield during the production test, so that the drilling ship not only served as the operation platform of production test facilities, but also retained the drilling operation function of the original drilling platform. Because there are many operations and technical specialties involved, especially when multiple operations are carried out at the same time, the difficulties encountered are even greater. In the process of solving various technical difficulties, the system is the first at home and abroad. On April 5, 20001year, this technology was awarded "technical patent" by the Intellectual Property Office of the People's Republic of China.
The main technological innovations are as follows.
1. Transform and develop the operation function of jack-up cantilever drilling ship.
From deck layout of drilling ship, division of functional areas, electricity and water supply, load check and control to various related auxiliary operations, the design and transformation have been carried out.
The whole operation deck of the drilling ship was rearranged and designed, and different functional areas and explosion-proof areas were divided, and the load and function were verified, and various working conditions, oil production and test conditions were systematically designed and installed. In addition, power generation, power supply, heat supply, gas supply, water supply and personnel accommodation conditions are planned and verified, and berthing and hoisting operations are also designed and arranged.
2. Build a simple two-layer wellhead platform.
Using the 30 "riser of Caofeidian 1-6- 1 well and Caofeidian 1-6-2DS well, a simple double-layer wellhead platform was built. In addition, as the operating platform of the blowout preventer, the wellhead lifting platform of the drilling ship meets the installation and operation requirements of drilling blowout preventer, production wellhead and testing blowout preventer. Structurally, two wells' riser transverse connection reinforcement and drilling ship transverse connection reinforcement are adopted to make the platform meet the safety requirements of drilling and oil production testing. At the same time of trial production in Caofeidian 1-6- 1, well Caofeidian 1-6-2DS was drilled, and the final well depth (well deviation) exceeded 3000m.
3. Production string structure
In order to meet the requirements of production, testing and safety, according to the technical specifications, an electric pump wellhead and a Christmas tree are installed at the wellhead of the oil well. Y-shaped pipe string is used to install electric submersible pump and downhole safety valve. In the actual testing process, various pressure and production tests, shut-in pressure recovery tests and high-pressure physical property sampling were carried out.
4. Oil and gas processing technology and oil transportation facilities
Adopt the simplest design and make the oil and gas treatment process meet the requirements of testing, metering and transportation, and design and install related equipment according to the requirements of safety production specifications, so that the process and facilities have the functions of leak detection, alarm and emergency shutdown.
(2) Expand the application of test system results.
1. Modify the oil recovery index of this well according to the DST test.
This well has passed two systematic well tests, and the average oil production index is 529 m3/MPa d, which is about 1/3 ~ 1/2 lower than that calculated by DST test.
2. Determine the reasonable working system and output.
When determining the reasonable working system of this well according to the changes of different chokes and oil production, the chokes should be below 18.26mm, and the output should be controlled at about 530 m3/d. ..
3. Prove the oil-water interface and petroleum geological reserves.
Using the extended test data, the oil-water interface is calculated to be 2946m (previously determined oil-water interfaces are 2900m and 2950m), and the geological reserves of this oilfield are calculated to be 400× 104 ~ 420× 104 t, which is 43 1× 104t compared with the original volume method.