Improving the oil recovery of old oil fields meets the actual needs.
At present, the global average crude oil recovery rate is 35%, and the global average conventional natural gas recovery rate is 70%. The remaining reserves of old oil fields are still considerable, and the oil exploration potential is huge, which will still be the main force of global oil supply in the future. Therefore, it is a realistic choice to constantly explore new technologies and maximize the value of old oil fields. If the global oil recovery ratio is increased by 1%, the recoverable reserves will increase by more than 5 billion tons, which is equivalent to the global oil consumption for two years.
There are five main problems in the development of old oil fields: first, the progress of resource replacement and follow-up is slow, and it is difficult to use new reserves; Second, the water content continues to rise, and the relationship between underground oil and water is complicated; Third, the casing is seriously damaged and the infrastructure is aging; Fourth, the output of single well is low, and the contradiction between input, output and cost is increasingly prominent; Fifth, the treatment of pollutants is not fully up to standard, and environmental protection issues are outstanding. The main solution is to find out the remaining oil and optimize the reservoir management, so as to improve the single well production and recovery ratio, and finally achieve the purpose of optimizing the cost and prolonging the economic life of the oilfield. At present, global oil companies are taking active actions to achieve higher oil production targets.
20 14 Statoil established EOR (enhanced oil recovery) business department to increase offshore oil recovery to 60%.
In 20 12, Malaysia started the world's largest EOR project, which was used in baram Delta Oilfield and North Sabah Oilfield, which increased the oil recovery rate of these two oilfields to about 50% and extended the production period to 2040.
Russia implements preferential tax policies for old oil fields, stipulating that the higher the recovery degree, the greater the preferential margin; The difficult-to-exploit oil reserves are subject to differentiated collection of exploitation tax, and the old oil fields in Yamal-Nenets Autonomous Region are exempt from natural resource exploitation tax.
Technology and development direction of enhanced oil recovery in old oil fields
At present, enhancing oil recovery requires efforts in secondary and tertiary oil recovery. The main methods are water flooding, maintaining bottom hole pressure, thermal recovery, gas flooding, chemical flooding and other methods (such as microbial flooding). According to the statistics of China Institute of Petroleum Economics and Technology on the number of various EOR projects in the world in 1980-20 12, thermal recovery technology, as the first technical means of EOR, has kept the number of projects over the years.
In recent years, the number of carbon dioxide flooding projects has increased year by year, becoming the second largest EOR technology after thermal recovery. The number of chemical flooding and non-CO2 gas flooding projects is gradually decreasing, and the number of thermal recovery projects remains stable.
At present, the key technology series of exploration and development of old oil fields includes three categories: remaining oil description, improved water flooding and new generation EOR technology.
1. Description of Remaining Oil The description of remaining oil is to find the remaining oil accurately by using new technology, and describe the position and formation of remaining oil more clearly, which is the basis of reservoir management and enhanced oil recovery. Fine description of remaining oil has become the future development direction of this kind of technology. Specifically, with the deepening of reservoir exploitation difficulty and the increase of production performance data, fine geological characteristics research and remaining oil distribution description are carried out, reservoir geological model is improved, and remaining oil distribution is quantified. It needs the cooperation of geophysical prospecting, geology, reservoir and logging. This kind of emerging technology mainly includes four-dimensional seismic technology, optical fiber detection and nano-robot.
(1) Four-dimensional seismic technology Four-dimensional earthquake is to study the changing characteristics of fluids in the formation through repeated observation. Its technical advantage lies in that it can be used in the whole cycle of oilfield development: protecting the basic productivity of oilfield at the initial stage of development; Oilfield management and effective development of resources can ensure high economic benefits in the medium term; In the later stage, the oilfield development period will be extended and the ultimate recovery ratio will be improved.
(2) Permanent optical fiber downhole dynamic monitoring technology Optical fiber sensor reservoir monitoring is to use optical fiber sensors to test downhole multiphase flow, temperature, pressure, liquid holdup and other parameters in the process of oil exploitation, so as to understand the liquid production situation of oil wells and water injection situation of water injection wells. The dynamic detection of these information provides conditions for better reservoir management: it is beneficial to optimize the production and life of oil wells and water injection wells; Fault diagnosis and monitoring of intelligent completion; Monitor the steam flow and the efficiency of SAG-D, and monitor and confirm the efficiency of underground operation in real time; Improve reservoir incentives and remedial measures, such as observing the height growth of fracturing fractures in real time during fracturing treatment.
(3) The reservoir nano-robot is a kind of nano-sensor, which enters the reservoir through water injection. During the underground "trip", we can analyze the pressure, temperature and fluid type of the reservoir, and store the information in the memory, which will be produced and recovered by the production well with the crude oil. In practical application, they can help to delineate reservoir range, draw fracture and fault patterns, and identify and determine high permeability channels; Search for oil and gas missed in the oilfield, optimize well location, and design and generate a more realistic geological model; Transport chemicals to the depth of the reservoir to improve oil and gas production; Understand cross-well matrix, fracture and fluid properties and oil and gas production changes; It can be completed by direct contact with the reservoir, which plays an important role in the discovery and exploitation of remaining oil. It is worth mentioning that Saudi Aramco put forward the concept of nano-robot in 2007, carried out feasibility test in 2008 and field test on 20 10, and the technology became more and more mature. In addition, Advanced Energy Alliance (AEC), which is composed of many well-known oil and gas enterprises in the world, has been committed to exploring and producing oil and gas by using nanotechnology, developing underground micro-sensors and nano-sensors, and characterizing oil reservoirs and their fluids in three dimensions, so as to better characterize oil reservoirs and effectively develop oil and gas resources. 2. Improve water flooding Improve water flooding mainly from two directions to improve water flooding effect. On the one hand, it is necessary to study methods to improve downhole technology and water injection technology, such as downhole oil-water separation and layered water injection in intelligent wells; On the other hand, it is necessary to change the water quality of injected water, and change the wettability of reservoir rock surface by adjusting the ion composition and salinity of injected water, so as to improve oil recovery. The main methods are low salinity water flooding, intelligent water flooding and intelligent fluid flooding, which are characterized by using the existing water flooding equipment to obtain higher oil recovery with the least investment. At present, BP, Saudi Aramco, Shell and other companies have carried out field tests of low salinity water flooding and intelligent water flooding technology, and the results are good. Laboratory experiments improve oil recovery by about 40%; Single well test improves oil recovery by 6-12%; The field test shows that the effect of increasing oil production is obvious and the water production of oil wells is reduced. At present, the representative technologies in this field are: (1)LoSal low salinity water flooding technology, which can improve oil recovery as high as 10%. Since 2005, BP has injected low salinity water into the formation through an improved hydraulic device in Alaska Oilfield, and the oil production effect is obvious, and the water production rate has decreased from 92% to 87%. (2)SmartWater intelligent water drive technology. Intelligent water drive field test production equipment has carried out single well tests in carbonate reservoirs such as Ghawar and Kindom in Saudi Arabia. In Kindom's first field test, the residual oil saturation around the oil well decreased by 7%. At present, multi-well intelligent water injection field test is being carried out to study the influence of intelligent water injection on the ultimate recovery ratio of the whole reservoir, and it is estimated that the recovery ratio will be increased by 8%- 10%.
3. A new generation of EOR technology, mainly including gas drive and microbial oil recovery technology.
(1) EOR technology of gas flooding Carbon dioxide (CO2) flooding is the main technology in gas flooding. According to the statistics of 20 12, there are more than 100 CO2 flooding projects in the world, of which about 90% CO2 flooding projects are concentrated in the United States. CO2 flooding has become the first technology to enhance oil recovery in the United States, with an annual output of150,000 tons and an annual injection of 30 million tons of CO2. The "new generation" CO2-EOR technology can eliminate the problems of viscous fingering and immiscible flooding by increasing CO2 injection, optimizing wellbore design and layout, adding polymers or other tackifiers, and adding additives to reduce the minimum miscible pressure, so as to reduce the remaining oil saturation in reservoir pores after water flooding and make the remaining oil flow again, which has a good application prospect in remaining oil areas. Remaining oil zone (ROZ) refers to some oil-bearing intervals that have no economic oil production in primary oil recovery and secondary oil recovery. Roz is usually located under the main pay zone of conventional oil fields or in the early water migration channel between conventional oil fields, and its reserves are extremely rich, reaching 654.38+04 billion barrels. The development of ROZ is expected to increase the recoverable reserves of crude oil in the United States by 30%-50%. At present, the main development mode of ROZ is miscible CO2-EOR. With the application of the improved "new generation" CO2-EOR technology, the output of ROZ has increased obviously, but the lack of sufficient cheap CO2 supply will hinder the output from reaching a higher level. By the end of 20 12, the Permian basin in the United States had implemented the 1 1 ROZ project, and the daily oil production exceeded 13000 barrels. Six ROZ projects are planned to be implemented in the future, and the time of new projects depends on the effectiveness of CO2 supply.
(2) Microbial oil recovery technology
Principle of bio-enzyme flooding technology: A special bio-enzyme preparation is injected into the stratum, so that the wettability of rock changes from oil to water, the interfacial tension between mineral particles and oil phase decreases, and the flow resistance of fluid through the pore throat decreases, thus increasing oil. Mann oilfield in Myanmar is an old oilfield that was put into production on 1970. After adding enzyme, the water content decreased greatly and the oil production was relatively stable.
AERO (activated environmental oil recovery) technical principle: optimize water quality by producing nutrients, so that microorganisms can multiply rapidly. Activated microorganisms can use crude oil as a carbon source and as a surfactant to reduce the interfacial tension between oil and water, and oil is released into the water flow; Microbial reproduction blocks large water flow channels, forcing water to choose other flow paths and driving more stranded crude oil. Once the pneumatic system is started, the procedure will be repeated until all the residual oil is drained. The system can extract up to 20% of the hard-to-produce crude oil in the formation, which can increase the crude oil production in this area by 9%- 12%. Using existing production equipment and infrastructure, there is no need to drill new wells.
Application of microbial oil recovery technology: microbial oil displacement technology is considered to be the most potential oil displacement technology in the United States. According to statistics, the reserves available for microbial oil recovery in the United States are as high as 649 billion barrels, accounting for 58% of its total reserves. In the past 20 years, the U.S. Department of Energy has supported 47 research projects on microbial oil recovery, 8 of which are under way. Microbial oil displacement technology is being widely tested in the field, and its research results show that the implementation of microbial oil displacement technology in the later stage of water injection development can improve oil recovery 16%.
Russia has mainly carried out the research on endogenous microbial oil displacement technology, and has also entered a large-scale industrial application. The old oilfields such as Romashkin, Bashkorstan and Tatar have increased oil production by 600,000 tons, thus prolonging the development life of oil reservoirs.
The Norwegian National Petroleum Corporation has carried out the world's largest experiment of microbial flooding technology in Norne Oilfield of Beihai Oilfield, which has achieved great success and is expected to increase crude oil production by 30 million barrels. Norway's national oil company also regards microbial oil recovery technology as the main research direction in the future.