Research On A Detection Method Of Oil Well Dynamic Fluid Level Based On The Column Sound Field Model

The supply capacity of oil well, and relationship of the supply and discharge can beaccurately understood by detecting the fluid level depth of well, which will determine thesinking depth of the subsurface pump, and formulate reasonable oil production technology.Besides, it helps to ensure the related parameters, such as reservoir pressure, productivityindex, effective permeability, and analyze the abnormal reasons of the energy attenuation. It isof great significance to the reasonable formulation and adjustment of oilfield productionsystem.At present, the echo method is widely used in oil field to detect dynamic fluid level depthfor oil well. However, sound energy decreases sharply when the casing pressure is small, andthe received echo signal is very weak after sound waves involving collars and liquid surfacereflection. What’s worse, and waveform of echo signal is extremely complex, which isdifficult to identify, as a consequence of all kinds of noise superposition and interference. Howto detect the fluid level depth accurately is the difficulty of the current study, based on theissue that hitherto detection of dynamic fluid level depth is not precise enough.A detection method of oil well dynamic fluid level based on the sound field model of thecolumn is presented in this paper, inspired by the fact that the vocal frequency of windinstrument can reflect the acoustic pipe length. In this paper, we study on the oil casingannulus model of well column and depth of oil well fluid level, from the perspective of stringair resonance.Firstly, the typical string structure can be analyzed with the pipeline acoustic theory. Also,the relationship between the well dynamic fluid level depth and the natural frequency of thetube sound field is established, according to the sound field characteristic of the column andresonance theory of tube air column. Moreover, oil casing annulus air resonance model is setup by analyzing the pipe model with periodic collars, oil thimble pipe model and others.Secondly, the acoustic velocity is not constant in the well, due to the complexity ofunderground environment, where oil casing annulus contains natural gas, hydrogen sulfide, a large number of water vapor, and downhole temperature, pressure and other factors arechanged. Hence, Oil casing annulus is studied in some factors, such as temperature, humidityand pressure, involving the air resonance model, to modify oil casing annulus air resonancemodel.Thirdly, a sound frequency detection method for oil well is studied, and the method fordetermining the oil casing annulus air resonance frequency is designed. Moreover, a set ofexperimental device has been developed, which is used to detect the depth of oil well liquidlevel, through the design of hardware and software.Finally, a large number of experimental researches about simulating oil casing annulus,periodic collar string and horizontal wells are done to prove proposed method in this paper.The experimental results show the proposed method in this paper has excellent feasibilityand adaptability, providing a new way for the accurate detection of the well dynamic fluidlevel depth.