0 Introduction With the development of the petroleum industry, the development and production management of oil wells has begun to become intelligent and fully automated. Intelligent oilfield technologies such as “smart wells†and “smart reservoir management systems†are increasingly used and developed in the development of oil and gas fields, and downhole flow control technologies have become an indispensable and important branch technology of smart oilfield technology. The realization of this technology is mainly accomplished through an air flow meter installed downhole. By adjusting the opening and closing status of the flow controller, the flow of each production layer is controlled so as to finally optimize the output, increase the recovery ratio and reduce the energy consumption [1].
1 Development status of air flow meters Since the 1980s when multiphase flow measurement technology was studied, multiphase flow measurement technology has entered a relatively mature stage. Air flow meters are used not only in onshore oil fields but also in offshore platforms and underwater production. At present, the research and development activities of the new air flow meter technology continue unabated.
In recent years, suppliers have invested a lot of money in R&D to find new ways to measure multiphase flow, which has great potential in improving efficiency and can bring great economic benefits to users. Some downhole flow metering devices have separators installed that allow them to separate gas from the flowing liquid, which, to a certain degree, increases the accuracy of downhole flow metering.
Each technology has its own advantages and disadvantages, and their applicability depends on the condition, location and output of the well. Air flow meters use very sophisticated technology and are priced at about $325,000. It uses a variety of measurement techniques such as gamma ray density measurements on the mixture, with high accuracy, but for environmental considerations [2], some users are reluctant to use equipment containing radioactive materials.
1.1 Complete Separation Technology Complete separators are also called well test separators. This is a huge container containing a large number of samples of oil, water, and gas mixtures that have been mined. Once the container is filled with samples, the natural gas is discharged from above, the water sinks to the bottom, the oil floats to the surface of the water, and the sewage flow meter connected to the container can measure the volume of natural gas, oil and water, respectively. Well test separation has high accuracy and is widely recognized in the industry, but its large base limits its use on offshore platforms and underwater. The complete separator needs to rely on gravity to separate different flowing objects. This process takes several hours or even a long time, depending on the multiple oils, so the operator can only measure the average flow rate for a specific period of time. difference. The average price of the complete analyzer is 650,000 U.S. dollars, and the cost of use and maintenance are very high. After each use, the analyzer needs to be cleaned for the next use.
1.2 Partial Separation Technology Some separators are also called settling cyclones, as shown in Fig. 1. The basic principle is to solve the problem of multiphase flow by separating natural gas from oil and water. Oil, gas, and water enter a special cylinder at a certain angle. The centrifugal force generated by this process pushes the liquid out of the cylinder, leaving only gas inside. When the gas rises to the top, it is measured by a gas flow meter. The oil-water mixture is then metered through a moisture meter or other natural gas flow meter.
Figure 1 part of the separation flow meter
It can be judged in a timely manner whether a well is fully mined. Part of the cost of the separator is also low, about 250,000 U.S. dollars, its base is much smaller than the complete separator, and it can even be carried around. Operators can regularly measure old wells that may be under-produced, and verify whether a complete separator is invested. worth it. However, some separators may not be an ideal choice for measuring heavy oil because heavy oils are difficult to separate by centrifugation.
1.3 Non-Separation Technology The Venturi Specific Gravity Flowmeter [3] contains only three sensors and can measure multiphase flow rates and phase fractions without a slip model or even with high skew and backflow. The device is a simple combination of a standard venturi and a gamma ray pycnometer. The pycnometer has a very low radioactive source (<10 uci) and is used to measure the density of the mixture. The symbiotic function of the two devices (the venturi and the hydrometer) improves the utility and accuracy of the test. The key factor is the stirring function of the venturi in the metering process. The gamma ray hydrometer is downstream of the venturi. After the multi-phase flow is uniformly mixed, the fluid is metered where the slip disappears, as shown in FIG. 2 . Therefore, the venturi specific gravity flow meter can more accurately measure downhole multiphase flow.
Figure 2 Conceptual diagram Venturi gravimetric flowmeter is a new generation of equipment, as shown in Figure 3, with reliable performance, simple structure and easy installation, from which important values ​​can be extracted, especially when the flowmeter is installed with a good When the real-time data acquisition and control system is combined, high-quality data can be safely transmitted to remote locations and event reports and remote suggestions for wellsite function control can be made. Air flow meters rely on physical flow parameters, such as the test section (throat) of a venturi tube, which requires a steady flow of fluid through its cross-section and flow calibration.
Figure 3 Implementation diagram of venturi flowmeter
2 Development Trends of Air Flow Meters
2.1 The development of air flow meters in the direction of serving heavy oil development Exploration shows that heavy oil and super heavy oil have accounted for more than 50% of the world's total oil field reserves. Many large oil companies have spent a lot of manpower and material resources to overcome various problems in the development of heavy oil. New equipment and new theories are used to overcome the technical difficulties in heavy oil development and the challenges of flow monitoring. Major oil companies The oil content of each layer of the reservoir is determined by the respective flow rates of oil, gas, and water. In this challenging situation, after testing various air flow meters, they discovered the Venturi-gamma ray flowmeter (shown in Figure 4) that could solve the problem that other types of flowmeters could not solve [ 4].
This multiphase flow technology overcomes the problem of the accuracy of the mixed-phase flow test system. Test simulations and field use demonstrate that the uncertainty of the air flow meter is less than 2%. A few years ago, people thought that heavy oil reservoirs were not a good source of income. Now, in order to increase the world's energy demand, oil companies have proposed through research that heavy oil is the future of the oil industry. At the same time, the production of heavy oil requires a large amount of investment in technology. In order to obtain clear and accurate multi-phase flow data, it also requires a lot of effort on air flow meters.
Figure 4 Principle of multiphase flow technology
2.2 The Downhole Sewage Flowmeter Smart Oilfield Development System, which serves the development of smart wells, is a well completion system that can control, analyze, and manage oil wells from the ground in multi-level and multi-branch oil wells. It includes well monitoring and data evaluation. , analog and remote traffic and other work. The online real-time measurement of three-phase flow of oil, gas and water is an important part of the intelligent oil field development system. The main research is currently under the guidance of the three-phase mixture phase theory, using various types of precision sensors in oil, gas, Under water mixing conditions, the single-phase flow of oil, gas, and water is measured at the same time. Domestic research in this field has also been carried out for nearly a decade. Important progress has been made in related theories and technologies. Below the well Chuli flow meter is a new type of device that can adapt to the complex environment downhole, high measurement accuracy, suitable for downhole flow measurement and control.
Below the well Chuli flowmeter shown in Figure 5. After the downhole multiphase fluid flows through the homomixer, it can be approximately considered as a homogeneous fluid. When the fluid in the pipeline flows through the venturi, the flow section shrinks, the flow velocity at the contraction section increases, and the pressure decreases, making Wenqiu Before and after the tube pressure difference, and then calculate the flow rate based on the measured pressure difference. Finally, the phase flux of each phase can be obtained by combining the calculated phase fraction of each phase. Because it is very difficult to accurately describe fluid motion, it is usually to use some simple relationship established on the basis of assumptions to derive and establish a practically available theoretical formula for describing fluid motion. The principle of throttling flowmeters is derived from the Bernoulli equation and the continuity equation.
Fig. 5 Venturi of novel Venturi flowmeter 
The main purpose of the design of the venturi flowmeter flowmeter is to monitor it from any position in the oil development well and control the corresponding tools to perform actions. At the same time, in order to meet the requirements of the downhole measurement device for accurate sewage flow measurement and complex environment, it must be Developed sensors for high temperature and pressure conditions.
3 Conclusion With the development of the electronics industry, sensor technology is also improving, and now industrially produced sensors can meet the requirements of various environments and provide high-precision data. Just like this, the flow meter starts from the well surface and goes downhole. Due to the constraints of the conditions, the current technology is not sufficient to place the flow meter downhole during the heavy oil extraction process. For intelligent well completion systems, it has long been documented that gamma ray and venturi can be combined to measure the flow rate, while the Venturi tube flowmeter is bound to become an intelligent well completion system because of its unique structure and low cost. The preferred metering equipment.
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