In China's offshore oil fields, the basic proven geological reserves of heavy oil fields account for 65% of the basic proven geological reserves of all sea areas, and the geological reserves of Bohai heavy oil fields account for 85% of the total reserves of Bohai Sea, and most of them are concentrated in some large oil fields of 100 million tons to 100 million tons, which shows its pivotal position. More importantly, the Bohai Sea is the main sea area where CNOOC China's crude oil output will jump in the next five years. Improving the development effect and recovery ratio of heavy oil fields is an important strategic issue related to the recent large-scale production and sustained high-speed development of China Offshore Oil Corporation.
First, a new model of offshore heavy oil field development.
(1) The main modes of development and production of offshore oil and gas fields in China at present.
The development mode of offshore oil fields basically inherits the development mode of onshore oil fields: first, it is a one-time oil recovery, and at the initial stage of development, it relies on the energy of the reservoir itself to produce some crude oil. During this period, the main investment is drilling wells, and the oil production methods are self-injection and pumping. When the formation energy is reduced to a certain extent, water injection and gas injection development with the main purpose of maintaining formation energy will be carried out, and the so-called secondary oil recovery stage will be entered. During this period, the main investment is to establish water injection system (including water injection equipment, pipe network, etc. Up to now, tertiary oil recovery technology has not been adopted in offshore oil fields at home and abroad. The 10th Five-Year Plan of CNOOC and the 20 15 development plan are formulated according to this model.
Judging from the development history of petroleum industry, the formation of crude oil development modes of primary oil recovery, secondary oil recovery and tertiary oil recovery is the actual process of petroleum production, the result of people's deepening understanding of the law of petroleum exploitation and the embodiment of the continuous progress of petroleum development technology.
(B) the main problems of this model
This model has been proved to be successful in technology and economy by many onshore oil fields, and the adoption of this model in offshore oil fields is conducive to reducing risks, because its investment is carried out in stages and relatively dispersed, which is conducive to fund recovery. The successful practice of offshore oil field development and production at home and abroad also proves that it is feasible to develop offshore oil fields in China by using this model, but its existing problems are also obvious, and the reform space and development potential are huge.
Because the tertiary oil recovery technology of enhancing oil recovery and further high and stable production at home and abroad has not fully reached the standard, the current development model of the oilfield is actually based on water flooding to enhance the maximum oil recovery. The division of the first and second stages is quite strict and clear, and the tertiary oil recovery stage is only considered as an idea, so that the actual recovery rate does not exceed 30%, which makes the oilfield development and production time very long, the recovery rate is not high, the crude oil output is not high, or the stable and high production period is short, and the water content rises rapidly. Even if tertiary oil recovery technology can reach the standard and meet the design requirements, the ultimate recovery rate will be improved, but the oilfield development cycle will be greatly extended. Under the condition of certain oil recovery, the longer the oilfield development period, the lower its economic benefit. In other words, the benefit of this model is inevitably low, or there is still huge space and room for improving the benefit of oilfield development.
On the other hand, theoretically speaking, the core business of oil exploration and development should focus on two tasks at the same time, one is to vigorously explore and increase reserves as much as possible, and the other is to strive to improve the oil recovery ratio so as to make maximum use of the resources already mastered. But so far, due to the influence of history, society, economy and traditional ideas, domestic and foreign oil companies have focused on increasing exploration and reserves when formulating their core business development strategies. The focus of oilfield development is how to improve single well production and oilfield production, and how to prolong the time of high and stable production. To achieve high and stable production, they also rely on finding and using new reserves to a great extent, and rarely talk about ensuring high and stable production with the goal of improving the recovery ratio of existing reservoirs as much as possible. Therefore, the tertiary oil recovery technology to further enhance oil recovery after water flooding has been neglected for many years, so that the tertiary oil recovery technology to enhance oil recovery after water flooding has not made a breakthrough so far, which is also an important reason why this model can always exist.
Now scientific and technological progress has made it possible to solve this technology. If enhancing oil recovery is the development strategic goal of our core business, it may bring broader development space and greater potential for the development of our core business. Therefore, the existing mode is not the best mode to adapt to the characteristics of offshore oilfield development and production, and reform should be carried out to establish a new mode of offshore oilfield development and production.
(C) the basic concept of the new model
Limited by the development environment, characteristics and natural conditions of offshore oil fields, offshore oil development should focus on improving crude oil recovery and economic benefits, that is, taking into account the maximum economic benefits and crude oil recovery, and developing oil fields quickly and efficiently in a short period of time (platform service life).
How to make full use of advanced crude oil development technology to extract more crude oil economically and quickly is not only the requirement of economic benefit, but also the requirement of protecting and rationally utilizing resources. If the purpose is to make full use of petroleum resources, the current practice should be to first set the crude oil recovery target according to the latest technical achievements of petroleum exploitation and reservoir conditions (especially when the tertiary oil recovery technology that greatly improves oil recovery will probably make a breakthrough and development), and then, according to the characteristics (time limit) of offshore oil fields and current development technologies, formulate development models, conduct economic evaluation and formulate development plans in turn, so as to have
In recent 5 ~ 10 years, great progress has been made in crude oil exploitation technology and related technical fields serving crude oil exploitation, which has laid a technical foundation for the renewal of offshore oil development model and the improvement of development efficiency. These technologies include: technologies to improve oil well production (including horizontal well production technology, fracturing sand control technology, downhole lifting technology, etc.). ), technologies for improving oil recovery (such as polymer flooding and compound chemical flooding). ) and polymer chemistry, colloid chemistry, surface chemistry and chemical synthesis technology. On the basis of fully considering these technological progress, re-examining and demonstrating the development mode of offshore oil fields will promote the technological progress of offshore oil development and related fields in China.
Therefore, the basic idea of the new model is based on the latest technology in the field of crude oil development, with the development index of maximizing crude oil recovery and the goal of maximizing economic benefits as the development plan.
(D) the basic meaning of the new model
Relying on scientific and technological progress and scientific management, the development, production and management of offshore oil fields in China are planned, designed and developed with the basic starting point of greatly improving the recovery ratio of existing oil reservoirs (from 20% to 25% to 35% to 40% or even higher), so as to maximize the economic benefits of existing oil and gas fields and obtain more crude oil output in a limited exploitation period.
A design the development plan with the strategic goal of improving the oil recovery as much as possible (instead of aiming at the oil recovery that can be achieved by the existing technology). ① In the core business, increasing the investment in exploration technology to find more reserves is as important as trying to improve the oil recovery rate of the oilfield, and trying to improve the oil recovery rate is the strategic goal of development; (2) Increase the research of EOR technology, and form practical technology as the forerunner and technical guarantee of new mode as soon as possible; (3) Design the development scheme that can improve the maximum EOR (the target is 35% ~ 40%), leaving an "interface" for further EOR.
B Assuming that chemical flooding (polymer flooding and compound flooding) is up to standard and effective, polymer flooding can further improve the oil recovery after water flooding 10% ~ 12% (or higher), and compound flooding can further improve 20% ~ 25%.
C. Completely break the strict boundaries of primary oil recovery, secondary oil recovery and tertiary oil recovery, and use it as a means and a series of technologies for oil recovery and enhanced oil recovery under three different conditions. According to the reservoir characteristics and the latest development and production technology, the three series of technologies are integrated, optimized, combined and integrated to form a technical and economic development model and corresponding series of supporting technologies that can achieve the highest recovery rate in the shortest time, and realize the goal of "building an oil field in the shortest time when conditions permit". Taking Bohai Oilfield as an example, the existing oil recovery specified by ODP has been increased from 25% to 10% ~ 15% to 35% ~ 40%, which has optimized the primary, secondary and tertiary oil recovery, and the total development time has not been extended or further shortened, which not only greatly improved the total oil production of the reservoir, but also greatly increased the annual crude oil production.
(E) The basic content of the new model
(1) Make full use of the latest achievements of other disciplines, improve and perfect chemical flooding technology, and strive to improve the ultimate recovery ratio of offshore oil fields. At present, the primary oil recovery and secondary oil recovery technologies used in offshore oil fields in China have basically passed the test, which can completely meet the targets specified by ODP, while the secondary oil recovery and tertiary oil recovery after water flooding are completely ignored. At present, the offshore oil fields put into development have high overall permeability and strong heterogeneity, and the reservoir humidity and crude oil viscosity are suitable for chemical flooding or compound chemical flooding technology with the main mechanism of improving the viscosity of displacement phase and controlling liquidity. At present, polymer flooding enhanced oil recovery technology at home and abroad has made new development and major breakthrough, which may reach the level of meeting the needs of tertiary oil recovery in offshore oil fields in the foreseeable years. Therefore, in the middle and early stage of water injection development, tertiary oil recovery technology combined with corresponding advanced technology and production equipment can achieve the real purpose of improving oil recovery, making it possible to improve the final oil recovery by 10% ~ 20% compared with the original ODP requirements. This is equivalent to finding new oil reserves, providing technical support for CNOOC to increase production and reserves, and becoming the technical and material basis of the new model.
(2) Using high technology to speed up the recovery of primary oil recovery and shorten the time of primary oil recovery.
On the premise of not damaging the reservoir (or causing irreversible damage), the development plan is modified by using advanced technology and equipment, which greatly improves the oil well output and the annual crude oil output of the oilfield.
Under the condition of relatively perfect primary oil recovery technology, it is the first link of the new model to actively adopt new technologies and equipment to further increase the daily output of crude oil and shorten the primary oil recovery time. Using the advanced extended reach horizontal well technology at present, the controlled production area of oil wells can be expanded and the daily output of oil wells can be improved. Adopting high-quality rapid drilling and completion technology and further improving the whole process of reservoir protection technology can further improve the single well production. By using various liquid lifting technologies, the production capacity of oil wells can be expanded, modern well completion sand control technology can be done well, and the oil well output can be increased, so as to speed up the primary oil recovery and shorten the primary oil recovery time, gain time for implementing the reservoir enhanced oil recovery technology, and also provide the necessary "export" for the new model to produce more crude oil in a shorter time.
(3) Enter the secondary oil recovery stage ahead of schedule.
The shortening of primary oil recovery time is to enter the secondary oil recovery period in advance. More importantly, in order to greatly increase the daily output of crude oil, it is necessary to inject water earlier than before, so as to maintain this long stable production period under the action of maintaining formation energy and displacement mechanism. During this period, under the reasonable well pattern and water injection rate, the reservoir utilization degree is improved and the output is increased, and crude oil is exploited at a high speed and economically in the middle and low water cut period, which has achieved good economic benefits.
(4) Shorten the water injection development time and enter the tertiary oil recovery stage in advance.
There are several reasons for shortening the development time of water injection. First, due to the short validity period of offshore platforms, water injection development in offshore oil fields cannot last as long as that in onshore oil fields, so it is necessary to squeeze out time to implement enhanced oil recovery technology. Second, because the benefit of water injection development in the middle and late stage is not high. With the development of water flooding, the breakthrough time of water flooding in high permeability layer is short, and the water content of crude oil will continue to rise, which will affect the oil production index of the oilfield. Thirdly, the existing research shows that there is no strict difference and boundary between secondary oil recovery and tertiary oil recovery. Therefore, it is necessary to blur the concepts of secondary oil recovery and tertiary oil recovery, organically combine water injection development and tertiary oil recovery into a whole, and enter the oilfield development process in advance.
To sum up, the characteristics of the new model are as follows: ① In CNOOC's core business, efforts to improve oil recovery are taken as the strategic goal of oilfield development and production, and placed in the same important position as exploration. The guiding ideology of oilfield development is "to exploit crude oil in the shortest time to achieve the maximum oil production". It is the foundation and technical guarantee of this model to solve the polymer flooding technology as soon as possible at this stage and improve the oil recovery ratio by more than 10%. ② Adopting the latest oil development and production technology, the oil well output and oilfield productivity are greatly improved, the oilfield development speed is accelerated, and the primary oil recovery time is shortened. (3) The boundary between secondary oil recovery and tertiary oil recovery is blurred, and these two stages are combined as two series of technologies to improve oil recovery and make the oil field high and stable, which can greatly improve oil recovery and shorten the oil field development time, thus obtaining greater social and economic benefits.
If the above four links are feasible in technology and economy, the result of this model will be to greatly improve the utilization rate of oil and gas resources in China in a short time while ensuring high annual output of oil fields. Moreover, while speeding up the recovery of funds, it is equivalent to increasing the same oilfield by half with much less investment. This will greatly improve the utilization rate of offshore funds and reduce the risk of offshore development and production for offshore oil with economic benefits as the center.
(6) Feasibility analysis of new offshore oilfield development model.
1. Technology, equipment and market feasibility analysis for greatly increasing annual output.
At home, the current oil supply and demand market is in a state of oversupply, and this situation will continue for a long time. The processing capacity of domestic petroleum processing enterprises has not yet reached saturation. At the same time, with the sustained, healthy and rapid development of the national economy and the progress of petroleum processing technology, the demand for refined oil and petroleum processing capacity will further increase. Therefore, there is no market resistance for CNOOC to provide a large amount of annual oil production.
At present, all kinds of single technologies to improve the development speed of oil reservoirs are relatively mature, or they can be mature after short-term research. As long as they are organized, integrated and integrated, the purpose of speeding up primary oil recovery and shortening primary oil recovery time can be achieved. The early reservoir water injection technology is a mature technology in China, so it should not be a problem to use it in this model.
The tertiary oil recovery technology of chemical flooding to enhance oil recovery is the basis and key to form a new model. In recent 20 ~ 30 years, due to the unremitting efforts of experts at home and abroad (especially at home), great progress has been made in this field and it is on the eve of a breakthrough. As long as we concentrate our efforts, it is expected to break through in 2 ~ 3 years, forming practical technology of offshore oil fields and laying a technical foundation for the establishment and application of new models.
2. Development status of polymer flooding technology in China.
The theory and practice of enhancing oil recovery at home and abroad prove that for reservoirs suitable for polymer flooding and compound flooding, the oil recovery after water flooding can be increased by 10% ~ 20% as long as the performance of the displacement fluid of the displacement object meets the design requirements. The enhanced oil recovery by polymer flooding has entered the stage of industrial application in the main reservoirs of Daqing Oilfield, and its oil recovery is higher than that by water flooding by 12%. The pilot test results of ASP flooding in Daqing show that its recovery ratio is 20% higher than that of water flooding.
After tackling key problems in the Eighth Five-Year Plan and the Ninth Five-Year Plan, a series of supporting technologies have been formed for polymer flooding in China. Specifically, it includes the research on enhanced oil recovery mechanism of polymer flooding, rheological properties and seepage characteristics of polymer, detailed description of reservoir in the later stage of water injection, polymer screening and evaluation, numerical simulation of polymer flooding, reasonable well pattern design of polymer flooding, channeling prevention and reinjection technology of polymer produced fluid, surface injection equipment and economic evaluation of polymer flooding. The scale, effect and level of its specific application are leading in the world, but at higher temperature and salinity, the viscosity of polymer solution can not meet the design requirements, or it has not been widely popularized because of its high cost.
Compared with onshore oil fields, the main difficulties of polymer flooding in offshore oil fields are as follows: ① The polymer flooding in offshore oil fields requires good salt resistance, because the polymer flooding in offshore oil fields can only be prepared with high salinity seawater, and at the same time, due to environmental protection requirements, the produced sewage cannot be directly discharged and must be reinjected; ② The polymer is required to have good solubility, because the space of offshore platform is limited, and it is not allowed to build large-scale liquid storage tanks; ③ The polymer is required to have good viscosity increasing ability, on the one hand, because of the requirement of offshore polymer injection cost, and on the other hand, because of the high viscosity of underground crude oil in Bohai Oilfield, in order to realize liquidity control, the polymer solution must have high viscosity under the premise of economic permission; ④ The polymer is required to have good injectability and shear resistance, which is an inevitable requirement for large well spacing in offshore oil fields.
Thanks to the unremitting efforts of domestic experts, in recent 10 years, breakthroughs have been made in the research and development of polymers for oil displacement that adapt to harsh reservoir conditions, especially the successful development of a new hydrophobic association water-soluble polymer NAPS suitable for chemical flooding in high-temperature and high-salt reservoirs, which greatly expands the application scope of polymer flooding and compound chemical flooding, and the temperature has been extended to 90℃. The salinity is expanded to 5× 104mg/L, and the preparation conditions of oil displacement agent are expanded from clean water preparation to sewage preparation. Technically, it has the basic conditions to solve the above four problems of polymer flooding in offshore oil fields, which provides a guarantee for China offshore oil fields to adopt enhanced oil recovery.
Fig. 10- 1 viscosity-concentration relationship under different salinities (80℃, 7.34s- 1).
Figure 10-2 Viscosity-concentration relationship under different water quality (45℃, 7.34s- 1).
A. Figures 10- 1 and 10-2 are comparative experiments on the viscosity increasing effect of this polymer and HPAM under different conditions. The results show that this polymer can completely solve the problems of high-efficiency viscosity increasing, seawater preparation and sewage reinjection in offshore oil fields.
B. Due to the reversible association of hydrophobic groups on the molecule, the apparent viscosity of the new associated polymer solution increases significantly under low shear conditions. Under the condition of high shear, the association is destroyed and the apparent viscosity of the solution is reduced, which ensures that the polymer solution has good shear resistance and relatively low injection pressure. Figure 10-3 is the experimental result of polymer solution injection ability evaluation, which shows that the well-dissolved NAPS solution has good injection ability and can effectively diffuse into the formation.
C according to the statistics of onshore oil fields, the time for oil wells to see polymer injection effect is directly proportional to the square of injection-production wells, and inversely proportional to the average permeability of oil layers between injection-production wells, with good correlation, as shown in figure 10-4. The high permeability of Bohai Oilfield provides favorable conditions for polymer injection under the condition of large well spacing.
D table 10- 1 shows that the new polymer AP has higher shear resistance than HPAM. It can be seen from table 10-2 that the oil displacement effect of the new polymer is better than that of HPAM. Table 10-3 shows that under the conditions of high temperature (70 ~ 80℃) and high salinity (5000 ~ 100000 mg/L), the associated polymer system still has a high oil displacement effect, which can improve the oil recovery after water flooding 10% ~ 20%.
Figure 10-3 NAPS injection experiment
Figure 10-4 Relationship between Effective Time and d2/K of Polymer Flooding Oil Wells in West Area
Table 10- 1 shear resistance of new polymer (stirring for l5min, salinity: 4000mg/L, 45℃, 7.34s- 1).
Table 10-2 comparison of experimental results of oil displacement between new polymer and HPAM
Table 10-3 core displacement test results under different salinity
The research of polymer flooding technology in China shows that the application conditions of a series of practical technologies suitable for polymer flooding to enhance oil recovery in offshore oil fields in China have been initially met. As long as we concentrate our efforts and increase investment, it is possible to make breakthroughs in the near future.
3. The influence of the implementation time of polymer flooding on the overall benefit of crude oil recovery in offshore oil fields-the possibility of fuzzy secondary and tertiary oil recovery stages.
The mechanism analysis of polymer flooding, the experimental results of indoor oil displacement and the field application results show that the timing of water flooding to polymer flooding has little relationship with the ultimate oil recovery, and the earlier the timing of polymer flooding, the better the comprehensive benefit.
(1) A large number of indoor core experiments show that there is little difference in the final recovery degree when polymer flooding is carried out at different water-cut stages. Han and Hu Jingbang used heterogeneous positive rhythm stratum model to simulate the experiment of the influence of polymer flooding timing on ultimate oil recovery. Table 10-4 and table 10-5 are the experimental results of HPAM and new polymer flooding in different water cut periods, and both of them reach the same conclusion: the magnitude of enhanced oil recovery by polymer flooding has little to do with the degree of reservoir water injection development (secondary oil recovery) during polymer injection.
(2) At different injection times, the economic benefits of polymers vary greatly. The influencing factors of polymer injection timing mainly include residual oil saturation and water content during polymer injection. Residual oil saturation is one of the main factors to ensure the effect of polymer flooding, and it is also the key factor to affect the effective time. Field statistics show that, under the same formation conditions, the higher the remaining oil saturation, the easier it is to form a crude oil-rich zone, and the earlier the effective time, the better the oil displacement effect. A large number of indoor physical simulation results show that the higher the degree of secondary oil recovery, the higher the water content of oil wells during polymer injection switching, and the worse the effect of polymer flooding on enhancing oil recovery. Han and Hu Jingbang's research and table 10-3 all reached the same conclusion.
(3) The field test results at home and abroad show that the injection timing of polymer has obvious influence on its effect. Ng3-6 in Area 8 of Gudong Oilfield is similar to Ng4 in Gudong Oilfield 1 Area, with similar geological conditions, similar reservoir properties and little difference in fluid properties. In Gudong Oilfield, Ng4 and 1 areas in Area 8 started polymer injection when the recovery ratio was 18.95% and 38.33% respectively. The field test results show that the effect of dehydration and oil increase in 1 area is far less than that in Gudong Oilfield Area 8. According to 29 field tests of polymer flooding in foreign countries during the period of 1964 ~ 198 1 year, among the 16 tests started near the end of primary oil recovery, 12 were successful. Only 1 of the 7 tests started in the secondary oil recovery stage was successful; Of the six tests started in the tertiary oil recovery stage (after water injection), only 1 test is barely effective. It can be seen that the earlier polymer flooding starts, the more promising it is to achieve good results.
Table10-4 Influence of HPAM polymer displacement timing on oil displacement effect
Table 10-5 Influence of New Polymer Displacement Timing on Ultimate Oil Recovery
To sum up, theoretical and experimental research and field practice show that there is no strict boundary between secondary oil recovery by water flooding and tertiary oil recovery by polymer flooding for reservoirs suitable for polymer flooding. As long as the polymer flooding technology passes, the timing of water flooding to polymer flooding has little effect on the final total oil recovery, but the economic benefits are quite different. Water flooding and polymer flooding are no longer two different stages of oil recovery, but two series of supporting technologies that can improve oil recovery to 40% ~ 50% and get comprehensive application. Their reasonable application can not only significantly improve oil recovery, save injected water, improve polymer injection efficiency and improve oilfield development efficiency, but also shorten or eliminate the secondary oil recovery stage, thus greatly shortening the oilfield development cycle, making it technically possible to achieve the goal of "achieving the highest oil recovery in the shortest time allowed by conditions" and making it technically possible to establish our new model.
(VII) Effect prediction of the new model
Bohai Oilfield is the main production capacity construction area of offshore oil in China at present. Until 20 15, most of China CNOOC's crude oil production will come from Bohai Oilfield. Therefore, its development effect plays an important role in the crude oil output and overall development of China Offshore Oil Corporation. Taking Bohai Oilfield as an example, the significance of the new model to offshore oil development is illustrated.
The application of the new model 1. will significantly improve the development benefit of the oilfield.
Take Nanpu 35-2 Oilfield as an example, which is scheduled to be put into production in 2003. According to the current ODP plan, the output in that year was 33× 104t, and reached the maximum output in 2005 in the third year 133× 104t, then decreased, and the development was completed within 20 years, resulting in cumulative oil production 1084× 104t. The annual output is shown in figure 10-5.
Under the new model, if the oilfield development period is 20 years and 15 years respectively, the production plan is shown in figure 10-6. Compared with the existing model, the new model will increase crude oil production by 640× 104t, with an increase rate of 59% and an increase in output value of about 6.4 billion yuan.
Figure 10-5 Production Plan of Nanpu 35-2 Oilfield (existing model)
Figure 10-6 Production Plan of Nanpu 35-2 Oilfield (new model)
2. It will provide technical support for 20 15 to complete and exceed the planned crude oil output, and may make the development plan of CNOOC20 10 by going up one flight of stairs.
Table 10-6 is a comprehensive comparison between the suggested crude oil production model and the existing model in Bohai Oilfield.
Table 10-6 Comprehensive comparison between suggested crude oil production model and existing model in Bohai Oilfield
It can be seen from table 10-6 that it is possible to make CNO-
The output of OC crude oil increased from 3000× 104t originally planned to 4629×104 ~ 5047×104t. If similar considerations are made in other oil fields, its output is likely to reach a higher level and the stable production time will be longer. This model can not only ensure the smooth implementation of CNOOC 20 15 planning, but also make CNOOC 20 15 development planning go up a step. If so, it will not only greatly promote the development of CNOOC, make a major breakthrough in its social and economic benefits, but also form a new offshore oilfield development and production model and its supporting primary, secondary and tertiary oil recovery technologies.
A. Take enhanced oil recovery as the strategic goal of oilfield development and production. At present, polymer flooding technology can improve oil recovery by more than 10%.
B apply various drilling, completion and oil production stimulation technologies to increase the output of single wells and oil fields as much as possible, and establish gathering and transportation processing capacity and technology and reservoir management system that match the stimulation.
C. According to the reservoir characteristics and the relationship between production and oil production, blur the boundaries of primary oil recovery, secondary oil recovery and tertiary oil recovery, rationally apply and optimize a series of technologies of primary oil recovery, secondary oil recovery and tertiary oil recovery, greatly shorten the time of primary oil recovery and secondary oil recovery or merge secondary oil recovery and tertiary oil recovery technologies, greatly shorten the development time of oil fields, and achieve the goal of "increasing crude oil production in the shortest time and making the oil recovery as high as possible". If this model and its supporting primary oil recovery, secondary oil recovery and tertiary oil recovery technologies can be successfully applied to other oil fields, its social and economic benefits will be infinite and it will certainly make greater contributions to the country.
Second, the Bohai heavy oil field with fewer wells and high production development new technology
Based on geology, oil reservoir, drilling, completion, oil production, offshore engineering and comprehensive economic evaluation, the latest research results and technologies of various disciplines are used to realize the study of "fewer wells and higher production" in Bohai heavy oil field, with the emphasis on the comprehensive study of geological laws, development strategies, ideas, methods, measures and technologies of Bohai heavy oil field, so as to solve the problems of low single-well productivity, low final single-well output and low single-well input-output ratio faced by Bohai heavy oil field at present.
(A) the "virtual" development of oil fields to be developed
In order to guide undeveloped oilfields to achieve "high production with fewer wells", reservoir description technology and reservoir numerical simulation technology are used to "re-compile" the development scheme of heavy oil oilfields with a long development history in various hypothetical modes, that is, virtual development research, including reserve production, well type selection, productivity design, adjustment strategy in different stages and "virtual" research to evaluate the oilfields to be developed, so as to explore the possibility of high production with fewer wells.
The preliminary conclusion of the virtual development research of Chengbei Oilfield is that by developing in stages, adjusting while drilling, and adopting new technologies such as multi-bottom wells and horizontal wells to improve productivity, the goal of fewer wells and higher production can be achieved. For details, please refer to the Comparison Table of Actual Scheme and Virtual Scheme in Chengbei Oilfield (Table 10-7).
Table 10-7 Comparison Table of Actual Scheme and Virtual Scheme Results of Chengbei Oilfield
(b) Successful application of new technologies to reduce the number of oil wells and increase production.
Taking Bozhong 25- 1 Oilfield (South) and Nanpu 35-2 Oilfield as examples, the oil fields to be developed are "virtually" developed by using horizontal multilateral well drilling and completion technology. The total number of development wells decreased by 8.3% and 18.3% respectively on the premise that the ultimate recovery ratio was close, which made it impossible to develop Nanpu 35-2 Oilfield because of its low economic benefit.
Table 10-8 Comparison of Scheme Effects between Bozhong 25- 1S and Nanpu 35-2 Oilfield
Figure 10-7 Production Plan of Nanpu 35-2 Oilfield
Nanpu 35-2 Oilfield is located in the middle of Bohai Sea. /kloc-0 was discovered in May, 1996, and the petroleum geological reserves were 9854× 104m3, of which the oil-bearing area was basically proved 16.4km2 and the geological reserves were 79 17× 104m3.
Nanpu 35-2 Oilfield is a nose structure complicated by faults. The reservoirs are the lower member of Minghuazhen Formation and Guantao Formation, with porosity of 22% ~ 44% and permeability of 50 ~ 50 ~ 5000 MD. The reservoirs are loose and easy to produce sand. The surface density of crude oil is 0.939 ~ 0.966 g/cm3, and the viscosity is 196 ~ 2000.
Nanpu 35-2 Oilfield is a compound oil and gas accumulation area with various types of oil and gas. Due to the influence of structural evolution, fault cutting and reservoir distribution, there are many sets of oil-water systems in the oilfield, and the oil-water relationship is complex. Since the discovery of the oil field, many rounds of reservoir research have been carried out, but it has been unable to meet the needs of internal profitability of offshore oil in China. In 2003, the horizontal multilateral well technology was adopted, which reduced the number of development wells, improved the oil well productivity (equivalent to 1.2 times the output of horizontal wells), reduced the drilling and completion cost, and enabled the development and construction project of Nanpu 35-2 Oilfield to start. Nanpu 35-2 Oilfield can be effectively developed, which shows a good prospect for the economic development of offshore heavy oil fields in China.