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论文范文
1. Overview Early kick detection is an important method in preventing blowout accidents and plays a significant role in deep-water drilling processes. As an important judgment factor, emphasis is always placed on the flow detection of drilling mud in an annular pipe. However, the complicated nature of underwater environment and the detection of the mud flow that can only be conducted at the mud outlet cause serious hysteresis in gas kick detection results. The serious blowout accident that happened in the Gulf of Mexico, USA, in 2010 was greatly connected with the hysteresis in gas kick detection results. Knowing how to realize the detection of mud flow rate inside the annular pipe near the seabed and identifying the occurrence of the gas kick accident as early as possible are of great importance. However, two kinds of fluid flow detection methods exist: intrusive and nonintrusive. The intrusive flow meter will damage the original pipeline system and influence the drilling of the mud field, which makes the application of the intrusive method inevitably affect the original technological process. However, the deep-water drilling technology is complicated, and the requirement is high; thus, the change of the original technological process will bring about a cost increase. To have no influence on the original technological process, the best option is to have a nonintrusive flow detection method. Ultrasound flow detection is a typical nonintrusive flow detection method; however, mud drilling will cause ultrasound attenuation, and the common ultrasound detection method cannot detect effective echo signals. The continuous ultrasound will form a strong sound field in the mud and can spread further than the impulse ultrasound for the wave superposition factor. Nevertheless, few methods exist for detecting the flow rate of the continuous ultrasound. In addition, the measurement of the nonintrusive flow is difficult, because the flow mode of the annular pipe mud is complicated and the pressure at the seabed is remarkably high. On this basis, this study analyzes the nonoriented reflection of the continuous ultrasound in the drilling mud and establishes models. This work obtains the principle that part of the reflected ultrasonic waves transfer into Lamb waves when the reflection signal enters into a pipe wall from drilling muds. From these principles, the relationship between the reflection signal frequency spectrum and flow rate can be obtained. The related flow rate detection algorithm finally solves the problem of the difficulty of applying ultrasound in deep-drilling flow detection. 2. Introduction Numerous studies and applications of mud flow detection exist regarding early kick detection [1]. In 1987, Speers and Gehrig [2–4] proposed the calculation of exit and entrance flows to detect gas kick; flow detection with ultrasound can accurately measure mud flow and it is suitable for both water-based and oil-based mud. Furthermore, Orban et al. [2–4] measured the mud flow rate using the impulse generated by the return mud in the pipe, which is not only appropriate for different types of mud but also suitable for a large measurement range. Steine et al. [5] adopted the Coriolis flow meter in measuring mud flow and proposed the use of an electromagnetic flow meter to measure water-based drilling muds. However, these methods have been used to measure mud flow at the well head. Although they have great advantages in terms of accuracy and measurement, a large amount of rising gas will be relatively close to the well head when a large change of mud flow rate occurs at the well head and the time left for dealing with the accident is limited. After gas kick occurs, a multiphase flow will be formed by the combination of mud and methane gas. However, the measurements of the multi- and single-phase flows are not the same. Many researches started to analyze the multiphase flow detection. Wang et al. [6] used the DOP2000 ultrasound flow meter to research on the Doppler ultrasound characteristics, such as emission angle and attenuation; their research provides guidance for the reasonable application of the ultrasound flow meter. Obayashi et al. [7] used several probes to detect fluid comprehensively, which not only obtains fluid speed but also detects the flow direction of the fluid at different positions. Their method is significantly supportive for fluid-type judgment. In the experiments, all these methods have been used with water or oil. However, in an actual situation, the attenuation of ultrasound is large in drilling mud and increases along with the growth of mud density [8], which makes most methods inapplicable. To detect the occurrence of gas kick early, recent researchers have move towards the use of a downhole instrument, including the methods of pressure while drilling and logging while drilling [9]. Collett et al. [9] analyzed various parameters when gas kick occurs, such as flow, pressure, density, and electrical conductivity. The detection method at the downhole location has great advantages in terms of accuracy and stability. However, the layout of devices and equipment at the downhole will certainly increase the cost and technological complexity. For gas detection, the ideal mud flow detection position is at the mud line of the seabed. Therefore, Zhou et al. [10] proposed the use of ultrasound to detect mud flow. Fu et al. [11] conducted further research and several simulation experiments. The experiment result proved the feasibility of measuring mud flow using ultrasound. On this foundation, the current study analyzes and builds models for the principle of ultrasound reflection in drilling mud and explains the relationship between mud flow rate and Doppler frequency shift under the condition of continuous nonoriented ultrasound reflection. 
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