Drilling fluid outlet flow is the key parameter for judging the well overflow in the drilling site. In order to achieve safe, rapid and economical drilling, it is especially important to perform quantitative, real-time and accurate monitoring of the drilling fluid. At present, domestically, the general logging instrument volume parameter monitoring and manual timing observation, recording, and comparison are generally used to determine whether there is an overflow or a lost circulation accident. This method of judgment has a low degree of automation and accuracy, and cannot be quantitatively detected, and the time of overflow detection is late. In recent years, new breakthroughs have been made in the quantitative monitoring technology of drilling fluids. Both mass flowmeters and electromagnetic flowmeters have been introduced for the quantitative monitoring of drilling fluids during oil drilling. Although the mass flowmeter has the advantages of high measurement accuracy and good stability, it has disadvantages such as high price and complicated on-site installation. Therefore, electromagnetic flowmeters are currently used to quantitatively monitor the drilling fluid flow at the drilling site. The electromagnetic flowmeter is limited by the measurement principle. To ensure the measurement accuracy, the fluid must flow through the flowmeter before and after the pipeline to meet the full-pipe state, which limits the installation and use of the electromagnetic flowmeter; when the flow rate of the drilling fluid is large, the fixed The electromagnetic flowmeter under the pipe diameter will inhibit the passage of fluid, which will cause backflow of the drilling fluid and affect the safe operation of the drilling.

In this paper, the hydraulic flow velocity field in the return pipeline of drilling fluid is simulated by hydraulics, the fluid flow law in the return pipeline is analyzed, and the structural design of the outlet flow monitoring system is optimized. At the same time, the drilling fluid quantitative monitoring over flow diverting device is designed to overcome the large flow. Drilling fluid return problem under state; thus satisfying full-scale measurement conditions of electromagnetic flowmeter, improving the applicability and measurement accuracy of the flowmeter, realizing real-time accurate monitoring of the drilling fluid outlet flow, accurate warning of overflow and drilling Safe construction provided support, which reduced the damage of well blowouts and killing operations to the underground oil and gas layers, thereby improving economic and social benefits and reducing the impact on the environment.

1 Status of Overflow Monitoring at Home and Abroad

There are many methods for monitoring overflow at home and abroad. The main research direction focuses on micro-flow monitoring and pressure monitoring. Microfluidic monitoring has been developed to include wellhead fluid level monitoring technology, drilling fluid flowmeter monitoring technology, improved flow monitoring technology, pressure monitoring, monitoring of drilling annulus pressure pressure monitoring technology, vertical pressure monitoring technology and acoustic wave monitoring technology. Guo Yuanheng et al. provided a comprehensive analysis of different methods for monitoring overflow from the aspects of improving equipment and analysis types [1]. At present, domestic monitoring of complex conditions such as overflows and kicks is generally performed by the comparison of the parameters of well parameters, comprehensive logging equipment volume parameters, and manual time observations, records, and comparisons to determine whether an overflow or leak has occurred. . This method of judgment is less automatic and accurate, and the overflow discovery time is late; in addition, the research work in the area of ​​early overflow monitoring also focuses on the accurate measurement of the volume change of the drilling fluid storage area, and thus the difference between the inflow and outflow of drilling fluid. Judgment overflow status. Because the basic volume of the storage area is large, the range of variation of the small flow rate is not easy to measure. In addition, the addition of auxiliary facilities is added to increase the complexity of the construction, and the fluctuation range of the liquid level is influenced by the environmental factors, thus fundamentally determining the measurement. Low precision and delays in finding early warning times. Usually, during the drilling process, there is a short time between the change of liquid level and the occurrence of blowout. Most wells have only 5 to 10 minutes of time from discovery of overflow to blowout, and some of them are shorter. Even overflow and blowout take place at the same time. There is almost no emergency. Processing time. The principle of overflow monitoring is not complicated, but due to the ambiguity and uncertainty of the overflow phenomenon, the limitations of measurement conditions and equipment, and the flaws of the monitoring scheme, the overflow monitoring will not achieve the expected results.

By analyzing the status of overflow monitoring at home and abroad, it can be seen that downhole pressure and formation factors are the causes of flow changes. Changes of other engineering parameters are the indirect effects of changes in fluid status, while the changes in fluid flow are reflection overflows. The most direct manifestation of the flow state is that the selection of export flow monitoring technology can be used as a breakthrough to judge the early overflow status, and it is also a reasonable choice based on the current status of logging technology in China.

2 Export flow monitoring system

2.1 Quantitative monitoring methods for export flow

The method is based on fluid dynamics calculation and analyzes the fluid flow law of the outlet pipeline. Considering the natural flow rate and the outlet pressure state of the fluid, the V-type outlet pipeline scheme is adopted. The flow meter test system meets the full-pipe state, and the inlet end inclination angle of the return pipeline is 30° to 45°. The calculation of Ansys fluid shows that in the angle range of 30° to 45°, with the increase of the angle of inclination of the inlet end of the return pipeline, the energy loss caused by the bent pipe of the branch pipeline is increased, and the Bernoulli at the rear test position is The constant value of the Lee equation C gradually decreases, so that the flow velocity value at the test position gradually decreases. Therefore, under the premise of ensuring the passing rate of the drilling fluid, the inlet end inclination angle should be reduced as much as possible; reducing the inlet end inclination angle to ensure another flow rate of another The advantage is also that it maintains the drilling fluid's cuttings carrying capacity, which is also confirmed in other research work.

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