I. Timely investigation and evaluation of on-site engineering projects to provide design basis for drilling and completion and offshore engineering design
The feasibility plan for oil and gas field development through optimization is proposed in the feasibility study stage, and this plan constitutes the basic framework of ODP, which generally does not change in the research stage of the overall development plan, and in fact does not allow any major changes. For example, the number and location of production platforms, the method of oil and gas gathering and transportation, and the scale of completed production. Because some related projects need to be carried out in a timely manner after the establishment of the ODP, and these projects will incur considerable costs.
(I) Environmental Impact Assessment Report
The EIA report is a necessary document when the overall development program of an offshore oil and gas field is declared to the state. The report is written by a department certified by the State Environmental Protection Administration with an environmental impact assessment certificate, and its purpose is to identify the current state of the environmental quality of the oil field sea area; predict the impact of the waste generated in each stage of the development of the oil field on the marine environment; analyze the possibility of accidental oil spills and the possible impact on the marine environment; and analyze the effectiveness and feasibility of the mitigation of adverse impacts in order to demonstrate the feasibility of the development project from the point of view of environmental protection, and provide the basis for the development of the oil and gas field. The feasibility of the project is analyzed to demonstrate the feasibility of the development project from the perspective of environmental protection, and to provide a basis for environmental protection and management of oil and gas fields in all stages of development. This is a highly specialized and substantial task, which needs to be entrusted to a well-known unit in the marine system.
Usually, the scope of the evaluation is limited to a few kilometers around offshore structures and pipelines, which requires nearly a million yuan in costs and a period of several months. In order not to affect the ODP schedule, this work is sometimes started at the feasibility study stage, so the framework of the program is unchangeable.
(II) platform site and submarine pipeline road routing engineering geological survey
Offshore oil and gas field ODP project, it is necessary to platform site, submarine pipeline engineering geological and engineering physical exploration survey. Its purpose is to identify the operational sea area seabed topography, geomorphological patterns, explore the medium and shallow stratigraphic structure, tectonics and a variety of potentially catastrophic geological phenomena, for the piling platform and submarine pipeline routing to provide engineering design, sea pipe laying, the platform installation of the soil parameters and design information required. For the platform, it is necessary to provide the geological conditions related to the offshore engineering construction and platform installation within the radius of 500-800m centered on the platform; for the routing area, it is mainly necessary to explain and analyze the bathymetry, geomorphology, and stratigraphic features within the depth of 0-25m in the strip-like range of 300-500m from the centerline of the sea pipeline. In addition, it is also necessary to investigate the environmental parameters in the operating sea area. This work is expensive due to the large amount of work and long period of time. Based on the information obtained after the survey, the program will not be changed unless it is absolutely necessary.
(C) the landing point of the sea pipeline and oil and gas gathering and transportation terminal site engineering geological survey
Half-sea and half-land type of gathering and transportation of the landing point and the land terminal, generally in the port or conducive to the construction of the dock area, through the landing point and the terminal site of the topography, tectonics, site stratigraphy, hydrogeological conditions of the survey, to make an assessment of the engineering geology, to provide the necessary design parameters of the terminal for the land. The engineering geology is evaluated through the investigation of the topography, structure and hydrogeology of the landfall and terminal site, so as to provide the necessary design parameters for the land terminal. Because this work also need to have a certain amount of field work, so in the establishment of the project should be carried out immediately.
Two, professional close connection and cooperation, improve the quality of the overall development program
The overall development program of the oil and gas field describes the complete process of oil and gas resources from the ground to the surface until the formation of commodities, the relationship between the various professions is very close, not only in the operation of the project should be considered in the profession of technical and economic issues, but also comprehensive consideration of the communication with the other professions and timely adjustment of ideas and programs, only in this way can we comprehensively consider the technical and economic problems. Ideas and programs, only in this way can we comprehensively improve the quality of ODP.
a. The selected oil and gas reservoir program provides the drilling completion and offshore engineering with relevant design parameters, such as the number of wells, wells, layers, extraction methods, construction scale, predicted production index, commissioning procedures, adjustments in the extraction process, etc., gives a risk analysis of the development program, and puts forward the requirements for implementation.
b. The drilling, completion and oil recovery process is based on the reservoir scheme, fully considering the implementation requirements of the reservoir for drilling and completion, optimizing the drilling design, selecting the completion method, determining the production method, calculating the wellhead parameters of the production wells as well as the electricity consumption for the use of mechanical oil recovery and artificial water injection, and selecting the type of workover machine, etc., based on the guidelines of adopting the advanced technology and saving. Provide design parameters to the offshore project and make drilling and completion cost estimates to be provided to the economic specialties.
c. Conceptual design of offshore engineering is mainly to confirm the design basis and basic information, process system (center platform and wellhead platform) flow design and heat balance calculation, utility system (seawater system, fresh water system, generator power system, fire-fighting and life-saving system, fuel system, discharge system, communication system, instrumentation and control, and fire detection system, etc.) flow design and facility selection calculation. Calculation and structural design of sea pipe process, structural design of offshore engineering such as conduit rack, group block, life module, single point, etc., demonstration of main scale performance of FPSO, demonstration and selection of form of single point, preliminary design of land terminal and investment estimation, which will be provided to the economic specialties.
d. Production and operation arrangements to determine the offshore platform and land terminal production organization and number of people, provided to the engineering design, to determine the size of the housing, describing the duties of each position, put forward the main points of operation and safety management points.
e. The main content of the safety analysis is to review whether the various norms used in the project are authoritative, to study the factors, consequences and countermeasures that may cause harm to the production facilities, to analyze the conditions of survival and operating conditions of the production facilities, to put forward the safety and protection systems, fire and life-saving systems and ambulance and medical facilities set up and described (provided to the engineering designers for the platform layout). The technical requirements of the safety facilities for the personnel, and finally to put forward the existing problems and recommendations, etc..
f. The project design must follow the national marine environmental protection regulations and standards for offshore oil exploration and development. marine environmental protection in the ODP mainly describes the sources of pollution and major pollutants (drilling stage, submarine pipeline laying stage, platform in place/installation/commissioning stage, production stage), risk analysis of environmental pollution (oil or gas spills), and put forward precautionary measures to control and manage pollution and make preliminary proposals. and treatment of pollution, and make investment estimates for environmental protection and provide them to the economic evaluation.
g. The economic evaluation mainly examines and summarizes the investment estimates provided by various professions, checks whether there are any omissions, duplications or over-budgeting; determines the annual operating costs during the development period; forecasts the price changes of the oil and gas that can be formed into the part of commodities; researches on the currency ratio and the interest rate; and researches on the distribution of the exploration costs and the way of recovering the development costs, etc., which are related to the economic evaluation. According to the year by year development index and operating costs to find out the break-even point, to determine the economic exploitation period and the economic recovery rate of oil and gas fields, to calculate the payback period and the rate of return on investment, through the sensitivity analysis of various important parameters to study the program's ability to resist risk.
h. Finally, the development project schedule should be prepared. Including from the basic design until the platform put into operation the time schedule of each stage of implementation, including offshore facilities (platforms, pipelines, platform upper facilities) procurement, construction, installation, commissioning and drilling, well completion, platform put into operation and so on. Key time points are set to ensure on-time production of the oil and gas field.
Three, all-round optimization of the program to reduce the development of investment
Relative to the project implementation stage of the investment budget and final account, the ODP preparation stage of the investment forecast is called an estimate. Due to the program within the head office once reviewed and approved and decided to implement, this ODP has a "legal" effect, in the process of implementation of the program can not be arbitrarily modified, the investment can not be broken, so the technology should be considered comprehensively, the investment estimate to have a considerable degree of accuracy, neither due to the investment is estimated to be too high and reduce the project's economy, or even to make the original benefits of the project can not start. So that the original benefits of the project can not start, but also not due to the investment estimate is too low to make the project after the start of the operation can not be operated. Finding ways to reduce the investment estimate is the basis for achieving a high rate of return in oil and gas field development, so each specialty in its own research field should consider not only technical advancement, feasibility and practicality, but also, more importantly, economy. Experience tells us that only by paying attention to saving investment in every link can the whole project obtain the best economic benefits, so each specialty must constantly carry out the balance between technology and economy and optimize the scheme repeatedly when researching ODP.
(I) reservoir program
Reservoir program is the foundation of oil and gas field development, a good reservoir program in the sea, first of all, should be underground resources as much as possible, and secondly is to create conditions for saving investment. The offshore reservoir program has always focused on how to get high production in the case of fewer wells. Fewer wells can make less investment in drilling, smaller platform structure, less equipment for oil recovery facilities, so as to reduce the investment in engineering and construction; fewer operating costs after the field is put into operation; the pursuit of high initial production can improve the payback rate, shorten the payback period, and effectively shorten the development period. Therefore, the reservoir program for offshore oil and gas field development should break through some traditional concepts.
1. Based on fewer wells and higher production
Offshore oil and gas fields have been put into production production well network density are very small, single well control reserves are very large, has been put into production and is building five heavy oil oil field average per square kilometer is only 3.46 production wells (including water injection wells), the average single well control reserves of 127.5 × 104t; 23 light oil oil oil field statistics well network density is only 1.35 wells/km2, single-well controlled reserves average 146×104t; 5 gas fields with a statistical well density of 0.122 wells/km2, single-well controlled reserves average 43.8×108m3.
Under such a well density, the designed oil recovery rate and the actual peak annual production of the field are much higher than that of similar oil and gas fields on land. Statistics show that the average oil recovery rate of heavy oil fields that have been and are to be put into production is 2.09%, and the average oil recovery rate of light oil fields is 6.12%, with the highest reaching more than 13%. The gas recovery speed of large fields is also high, and the gas recovery speed of Yacheng 13-1 gas field in the western part of the South China Sea is as high as more than 6%. The realization of high production from fewer wells, in addition to the unique geological conditions, the important thing is to change the concept of certain issues of oil and gas field development.
Fewer wells and higher production rate is the development principle of offshore oil and gas fields. The understanding of the relationship between oil recovery rate and stable production period is also changing in the development practice. Several high-speed extraction fields in the eastern part of the South China Sea put into production in the early 1990s, and the actual oil recovery rate was higher than the program design. Practice has proved that high-speed extraction does not reduce the crude oil recovery rate, but to shorten the development period, early recovery of investment, so as to obtain very good economic benefits. To the mid-1990s, the production of oil and gas fields from the preparation of the development program, will be less wells and high production as the principle of development of offshore oil and gas fields, basically changing the development of oil and gas field development in the past, always pursuing the "long-term stable and high production" development policy.
2. One set of well network exploits multiple oil layers and reduces the number of production wells
The practice of multi-layer oil field development has always been to use multiple sets of well networks to subdivide the development of layers in response to the non-homogeneous nature of the reservoirs. This is of course the best and most effective way to resolve interlayer conflicts, but on the other hand, it is bound to increase the number of wells. Basically, offshore oilfields adopt one set of well network to exploit multiple oil formations, and find ways to mitigate the loss of recovery rate due to one set of well network in the development program and oil recovery process. Huizhou 26-1 oilfield located in the eastern part of the South China Sea uses one set of well network, 20 development wells, and 3 stages (single-layer mining, layer system mining and inter-layer system mixing stage), and utilizes hole-filling technology to realize oil-bearing well section length of 635m, 9 sets of reservoirs of sub-recoveries. After 9 years of mining, the degree of extraction is 35.2%, of which the main layer is as high as more than 40%. Suizhong 36-1 heavy oil field located in the Bohai Sea also uses a set of 350m well spacing anti-nine-point well network to extract the oil-bearing well section length of 400m including 14 oil formation groups of two large sets of reservoir physical and fluid properties are quite different. Due to the loose lithology of the reservoir, it is impossible to make up the hole in stages, so it adopts the method of sand prevention in three sections, and the slip sleeve control between each section to realize the mining in three sections, and the recovery degree of the production test area reaches 102% in seven years.
Adjustment in the process of oil and gas field development is an indispensable and important means to improve the development effect. Offshore oil and gas fields in the development process due to the conditions do not allow a large number of additional drilling, one of the reasons is that the platform can not be adjusted for the drilling of wells, put into operation to reserve enough space, including enough well tanks and expansion equipment installation site, the platform structure can not withstand due to the increase in the number of wells brought about by a too large increase in the load; and secondly, drilling is difficult because of the adjusting wells are located in the initial network of wells in the production of wells in the middle of the wells, and the offshore Secondly, it is difficult to drill, because the adjustment wells are located between the production wells of the initial well network, and the design of drilling trajectories in offshore oil and gas fields must be carried out at the same time with the initial well network, nevertheless, it is quite difficult for the drill bit to pass safely in the middle of the clustered wells during the implementation of the drilling operation of the adjustment wells, and the cost of drilling will be increased greatly. Therefore, offshore oil and gas fields to achieve cost-effective development, must be based on the primary well network. Being based on a primary well network is not the same as not making any adjustments during the development process. With the continuous development of drilling and oil recovery technology, the development of offshore oil and gas field adjustment measures are mainly carried out in the original borehole, mainly utilizing the side drilling of worthless production wells or drilling individual supplemental wells in the reserved well slots on the platform. Offshore oil and gas fields attach great importance to the deployment of primary well networks, and the basic idea is to try to take care of the development of non-primary oil formations under the premise of ensuring that the reserves of the primary reservoirs are fully utilized, and for the areas and reservoirs that are not well controlled by the primary well networks, consideration should be given to the creation of conditions for the measures to be used in the future. For inefficient wells with low production, they are firmly removed in the process of well network optimization. Areas with thin thickness and small reservoir abundance are not spread wells in the primary well network.
For example, the heavy oil fields in the Bohai Sea, such as Suizhong 36-1, Jinzhou 9-3, Qinhuangdao 32-6, which have relatively large reserves, do not have wells in areas where the thickness of the oil layer at the edge of the field is less than 15m, and are prepared to use the edge of the wells in the later stages to drill horizontal wells or large-angle inclined wells to the outer side to increase the amount of movable reserves. Huizhou 26-1 oilfield in the eastern part of the South China Sea*** has 9 independent reservoirs, the development program is designed with 15 oil extraction wells and 5 water injection wells, initially 5 sets of main reservoirs are used, accounting for 74% of the reserves. 1991～1992 the field was put into production, and through the production, it was realized that the reservoir had sufficient water-driven energy, and there was no need for water injection, and all the 20 wells were production wells. The maximum oil recovery rate of the field was 6%, and the oil recovery rate of more than 5% was maintained for nearly 4 years. 1996, the water content of the field rose to about 60%, and 5 horizontal wells were drilled on the side of the old boreholes with high water content, and the development of the layer system was adjusted with the hole filling, which made the utilized reserves reach 100% without increasing the number of wellheads, and effectively improved the development effect, and the recovery rate was always stabilized at about 4%. By the end of 2000, the oil recovery degree of the whole field reached 39.48% and the comprehensive water content 74.2%.
3. Artificial lifting to increase the production differential pressure, improve the rate of oil recovery
For wells with the ability to self-spray, the past practice is to try to maintain self-spray. The development of offshore oilfield using mechanical oil recovery, not only because the wells stop spraying, a very important reason is to increase the production differential pressure to achieve the purpose of improving the output of a single well. The Huizhou oilfield group in the South China Sea has high production capacity and sufficient energy in the side water and bottom water, but when the development program was formulated, in order to achieve high production from a single well, it was designed to extract oil by gas lift (self-spraying, gas lifting, pumping and pumping at the same time), and the average production rate of a single well in the early stage of development reached 300-400t/d. In the oilfields such as Suizhong 36-1, Jinzhou 9-3, and Manqikou 18-1 in the Bohai Sea, the oil wells have a certain degree of self-spraying capacity. In order to achieve a higher rate of oil recovery, the development program are designed for mechanical oil recovery.
4. Full and rational use of natural energy, saving investment
Offshore oilfield development considerations as far as possible not to waste natural energy. For example, Huizhou oil field group in addition to the use of side water, bottom water energy drive oil, but also the use of gas reservoirs located in the upper part of the reservoir as a source of gas lift oil recovery; Suizhong 36-1 oil field, Qinhuangdao 32-6 oil field, the use of water reservoirs located in the upper part of the reservoir of the Dongying group of the Guantao group as a source of water injection for artificial water injection; platform output of dissolved gas for power generation and other platforms for self-consumption; the excess output of the gas through the economic evaluation, conditional It can be sold as a commodity (Bohai Manifold 18-1 oilfield group output dissolved gas is supplied to Tianjin city).
5. Joint group development of oilfields
Joint group development of oilfields creates very good economic benefits for small oilfields that cannot be started up individually. In the evaluation stage, pay special attention to the evaluation of the oil and gas field around the small structure, can be recommended to give priority to exploration, or in the development process of part-time exploration, once something is found, they can be used as a group **** a set of production facilities, will greatly improve the economic benefits of these oil and gas fields. For example, Huizhou 21-1 oil field, the preparation of the development program according to the recoverable reserves made by the economic evaluation results belong to the marginal oil field, at that time in order to make it economically viable, in addition to the use of high-speed mining, production wells, joint mining measures, but also the production facilities will be placed in the oil tanker in order to reduce the size and weight of the platform, it is this that creates the conditions for the joint development. After Huizhou 21-1 oil field was put into development, Huizhou 26-1, Huizhou 32-2, Huizhou 32-3, Huizhou 32-5, Huizhou 26-1 North oil fields were discovered in its vicinity, of which none of them had separate exploitation value except Huizhou 26-1, but due to the existing production tanker of Huizhou 21-1, the production facilities of the utility system and pipelines, etc., the fields were put into development and recovered their investment very quickly with a very small investment. put into development and quickly recoup their investment.
(2) drilling, completion and oil recovery process
Drilling and completion and oil recovery process design is the second important element of the overall development program, but also the beginning of the estimated investment. Offshore oil and gas fields are generally drilling and completion and oil recovery process costs account for 1/3 to 1/2 of the total investment, so we should try to meet the reservoir requirements under the premise of reducing drilling and completion costs by all means, and promote the localization of equipment. Reduce the cost has two meanings: one is to reduce the initial primary investment; in addition, we also have to consider the secondary or multiple investments after production, that is, consider the quality of the project and the life of the equipment, because the cost of repairing the wells in the offshore oil and gas fields is much higher than the land.
As for drilling wells, since all of them are directional or horizontal wells, the design should optimize the drilling trajectory and the structure of the well body, so as to save the tubing and reduce the difficulty of drilling, and to create the conditions for high quality and speed.
The main purpose of well completion is to carry out special research on oil and gas wells that require special completion techniques, which are technically more complicated and costly than normal cased hole completion, and the purpose of the special research is to determine the necessity of the special completion techniques. The purpose of the special study is to determine the necessity of the special completion process. Since any measures for the completion of offshore oil and gas wells must be completed before production, and there is no way to remedy the situation after production, this special study is particularly important. For example, in the Dongfang 1-1 gas field, where the gas component contains CO2, the preparation of the ODP included a special study of corrosion prevention in production gas wells, and through a comparative study of various methods of downhole corrosion prevention, it was concluded that the use of corrosion-resistant tubing and downhole tools was the only way to go. According to the standards set by NACE (National Association of Anti-corrosion Engineers) and the research results of NKK Company in Japan, it was determined that Cr13 alloy steel was used for downhole devices and runner parts in 6 wells, and the rest of the wells were made of 1Y80 material, so that different wells were treated differently and a lot of money was saved compared with using Cr13 in all wells. There is no obvious sand phenomenon when testing the gas wells in this gas field, but from the rock structure, sand may come out under the condition of high-speed mining, for this reason, sand prediction research was carried out, and the American AR-CO company and the British EPS company were asked to do the sand prediction of the gas wells. The result shows that the critical production pressure difference of sand out of horizontal well completion with cut seam tubing is about two times of conventional well casing injection, and the production pressure difference of production well design during production is much less than the critical pressure difference, therefore, the horizontal well production part of the production layer is completed with bare eye plus cut seam tubing and blind tubing, which has a certain anti-sand function, and it saves several millions of dollars of the completion cost.
Oil extraction process design, both the long-term practicality of the equipment to consider, but also to consider the life of the equipment, because oil recovery is a long process, even in the sea will be 15 to 20 years, so to choose a good performance, has matured process technology, although a larger investment, but the later investment is small and can reduce the operating costs, the cost of more is not excessive.
(C) conceptual design of marine engineering
Conceptual design of marine engineering is the main object of investment in the development project, a large project engineering investment to account for the total investment of 1/2 to 2/3, due to the content of the multi-professional, so it must be in line with the principle of spending less money to do more work and do a good job in order to optimize each design. The key points are to set the right design basis, select the right design parameters, correctly understand and use the specifications, optimize the design, reduce the facilities, simplify the process, optimize the layout, and promote the localization of equipment. Platform, FPSO and sea pipe are the three main projects of offshore oil and gas field development, and the first thing that affects the basis of their structural design is the environmental conditions of the sea area in which they are located, and the environmental conditions will change over time with a certain regularity and a certain degree of chance. Such as sea currents and waves in sea conditions, wind speed in meteorology, etc., all have different years (5 years, 10 years, until 100 years) of the recurrence period, we have to analyze a large number of statistical data from these, select the appropriate design parameters, which is very important for the structural design. Offshore oil and gas fields through many years of development practice to realize that, like the platform, the sea pipe such as permanent devices, as long as the production period to meet the production requirements and to ensure the safety can be, so according to the actual situation of the sea area reasonable and careful selection of the design parameters, can be a large number of savings in investment. When the quantitative impact of external natural conditions on these permanent devices is determined, the rest is to further optimize the structural design according to the parameters of the oil and gas field development itself. The conceptual design should implement the relevant laws and regulations of the state and China National Offshore Oil Corporation (CNOOC), as well as international standards, national standards and enterprise standards for structures, mechanical facilities, electrics, instrumentation, fire protection, communications, and so on. In particular, environmental protection and safety should be implemented in strict accordance with national laws and regulations, because the conceptual design is the basis of the basic design, and the basic design of the project has to pass the review of international or domestic famous classification societies, and the oil and gas field has to pass the review of the State Environmental Protection Bureau and the State Safety Office before the field is put into production, if the standard is not met will need to be rectified, so that the field will not be able to be put into operation on time, which will cause unnecessary losses in the economy. losses.
In addition to the design of permanent structures during the conceptual design stage, the main way to reduce investment is to optimize the platform facilities, including the optimization of gathering and transmission methods, the optimization of the total system engineering, the optimization of the utility system, the optimization of the platform facilities layout, and the optimization of the process flow. For example, in Suizhong 36-1 Oilfield Phase II Project, the conceptual design has repeatedly optimized whether the gathering and transportation method should be all-sea or half-sea and half-land. For Suizhong 36-1 oil field, we have the successful experience of nearly 5 years of development in the test area. For large heavy oil field which is not too far away from the shore and has hundreds of millions of tons of reserves, the half-sea and half-land type has a lot of advantages, but it involves a lot of problems that have not been encountered in the past, such as the landing point problem, the terminal problem, the problem of land requisition, the problem of wharf reconstruction, the problem of long-distance transmission pipeline of heavy oil, the problem of sewage discharge near the coast, and the relationship with the local administration, etc. All of them are the same as those in the past. The relationship with the local administration had to be re-examined. For this reason, we organized our forces to carry out research on many issues at the same time, and after confirming the technical feasibility, we managed to make the overall investment roughly comparable to that of the full-sea type, but in the long run, we saved the operation fee of the offshore part, and the overall economic benefits were better than that of the full-sea type. At present, the field has been according to the half-sea half-land gathering and transportation mode at the end of 2000 successfully put into production.
The study of the overall development of offshore oil and gas fields is a systematic project that involves many professions, many types of work, and many high technologies, and the process needs to be balanced and optimized many times, with the aim of achieving the high efficiency and high speed development of oil and gas fields.