Research On Theories And Methods Of Ultrasonic Detection On Methane Gas Kick In Deep Water Drilling

Gas kick detection is an essential part of safe well control in drilling.Recently,it is one of the hottest topics in safe well control research of oil and nature gas exploitation.The conventional gas kick detection methods are based on the drilling mud flow velocity measured near the well mouth which results in a high probability of delay.Meanwhile,the latest gas kick detection methods in research are based on measurement at down hole which results in the requirements of updating drilling process and devices,and making these methods expensive and hard to be applied.For deep water drilling,it is a feasible method with lower cost,less time delay to detect gas kick at mud line with non-invasive detection instruments.On this basis,the theory and method of non-invasive gas kick detection using ultrasonic at mud line are studied comprehensively in this paper.According to the different research levels,this paper mainly includes three aspects: gas kick detection theory and method,application program and experiment verifications.Gas kick detection theory and method:A complete set of theories and methods based on continuous ultrasonic to measure flow rate,void fraction and to detect gas kick are proposed.Firstly,the propagation characteristics,reflection characteristics of continuous ultrasonic wave,Doppler Effect in the gas-mud multiphase flow are analyzed according to the gas kick model and the gas-liquid multi-phase flow in the vertical pipe.Then according to the theory of waveform conversion and plate wave theory,the theory of plate wave will be produced by the ultrasonic wave reflected from particles in the pipe and the wave amplitude and frequency are related to incident angles is deduced theoretically.Based on the results of these theoretical analysis and the relationship between properties of received ultrasonic waves and different distribution of bubbles in different flow regimes,the destitution of particle velocity,incident angles,reflection angles,distance,and attenuation,a mathematic model of continuous ultrasonic wave is constructed.Through this model,the relationship between the received signal amplitude,spectrum and the fluid velocity,void fraction and flow regime in the annulus is established,and the corresponding mathematical expression is deduced.Finally,based on these theoretical bases,an ultrasonic detection algorithm for velocity and void fraction of gas-mud twophase fluid at the mud line in the annulus during deep water drilling is proposed.At the same time,a two-stage gas kick detection algorithm is also proposed,which uses the flow velocity and void fraction to make the preliminary judgment,and then higher level alarm will be raised according to the change of the flow regime detected by the shape of the received signal spectrum.Finally,the feasibility of distinguishing the solid particles from the gas bubbles is analyzed by the difference of their ultrasonic reflection,density and deformation characteristics.Application program : Two application programs based on a single detection equipment and multiple detection equipment is proposed.The program includes the installation of detection devices,communication methods,gas kick multi-level alarm algorithm,hardware design and software design and other aspects.The gas kick multilevel alarm algorithm combines the detection results of velocity,void fraction and fluid regime,and verifies the detect results logically according to the gas kick model.The detection algorithm makes a good balance between time delay and accuracy of the detection with multi-level alarms.Experiment verifications:Two sets of gas kick simulation platform is designed-the water and drilling mud experiment platform.The water experiment platform concluding a transparent observation window,is used to verify the basic theory and method proposed in this paper.Three experiments,empty pipe experiment,detect location experiment and plastic ball experiment,were designed to verify the existence of the plate wave and the deterministic relationship between the signal spectrum and the velocity and size of the reflector in the fluid.These experiments also verified the correctness of the proposed model indirectly.And the mud simulation platform can realize the precise control of methane gas filling and pressure.There are also three deigned experiments,velocity experiment,void fraction experiment and simulation experiment of the dissolution and precipitation process of methane gas in mud in gas kick model.The experimental results show that the velocity detection method proposed in this paper can accurately detect the mud flow rate.The maximum relative error of the measured results between the proposed method in this paper and the target flowmeter is less than 10%,and the void fraction experiment results show that the proposed detection method can effectively measure the void fraction when it is bigger than 3%.The effectiveness of the proposed method is verified by the results of simulation experiment of the dissolution and precipitation process.Finally,some special phenomena in the experiment process are listed and the reasons are explained.Meanwhile,the problems in the current research and the future research direction are also listed.