The Study On The Response Characteristics Of The Directional Electromagnetic Propagation Resistivity Logging

Directional electromagnetic propagation resistivity logging tool contains the axial coils, tilted coils and horizontal coils. It can provide phase difference and amplitude ratio with multiple depths of investigation. It greatly improves the directional detection ability, azimuth sensitivity and the amount of information of LWD electromagnetic propagation measurement technology. It improves the prediction ability of drilling ahead. It is especially suitable for geosteering in the thin reservoir, recognisng oil-water interface, and determinating and forewarning of complex formation. The thesis studies theory of directional electromagnetic propagation resistivity logging, designs the coil parameters of the tool, researches and analyses the influence of various logging environment on the directional electromagnetic propagation resistivity logging response. The contents are divided into following four parts:The first part expounds the structure and measuring principle of the directional electromagnetic propagation resistivity logging tool. Starting from the measuring principle of electromagnetic propagation resistivity logging tools, the calculation formula of tilt coils electromagnetic response and coordinates system transformation are reduced, and the amplitude ratio and phase difference calculation formula of the directional electromagnetic propagation resistivity logging tools measuring signal are expounded.The second part completes the parameters design of the directional electromagnetic propagation resistivity logging tools coils. Calculate the response of the directional electromagnetic propagation resistivity logging tools under different coils parameters through COMSOL finite element numerical simulation software. Analyse the influence of these coils parameters such as tools working frequency, transmitting and receiving coils’ tilt angle, and the space between transmitting and receiving coils on the instrument response characteristics. Design properly coils parameters of the directional electromagnetic propagation resistivity logging tools. The results show that the received signals’ amplitude is small, the attenuation speed is slow and the detection range is wide, but it is not sensitive to the formation conductivity when the working frequency of the tool is low. In homogeneous formation, the bigger the coil’s tile angle, the smaller the received signal amplitude and the faster attenuation the phase angle. When different contrast ratio formation exsists, the layer interface position and the conductivity contrast on both sides can be recognised by taking advantage of the cross component. When the space between transmitting and receiving coils is short, the received signal is influenced by direct coupling signal more than the formation conductivity changes. Increasing the space between transmitting and receiving coils can increase the detection depth, however, if the space is large, the receiving coils’ voltage amplitude decreases, ang it will be affected by noise easily.The third part researches the borehole effect and environmental impact on the directional electromagnetic propagation resistivity logging. Firstly analyse the influence of the four parameters that wellhole radius, eccentricity, mud and formation conductivity on eight coils of the tools. The results show that when the tool is centric in the wellhole, the response of the receiving coils near to the transmitting coil are affected seriously by wellhole radius, mud and formation conductivity, on the contrary, the response of the receiving coils far away from the transmitting coil are affected slightly. When the tool is eccentric, the receiving coils R3 and R4 can respectively detect the eccentricity of x direction and y direction. When the mud conductivity is great, the receiving coils far away from the transmitting coil are seriously influenced by eccentricity, and with the increase of eccentricity, the effects increased gradually. Secondly analyse the response of directional electromagnetic propagation resistivity logging under the invasion and shoulder environment. Inspect the influence of various factors of the invasion and shoulder, the results show that under the environment of invasion, the amplitude attenuation and directional phase shift of the signal received by the receiving coils near to the transmitting coil are bigger. When the shoulder exists, the logging response is affected by layer interface. The directional amplitude attenuation generates an angle at the layer interface, and the angle’s peak value increases. This phenomenon is helpful to predict the existence of layer interface before drilling. When the resistivity contrast ratio of target layer and shoulder layer is very big, the directional phase shift peak of receiving coils far away from the transmitting coil at the layer interface flips down, in this case, the phase shift cannot be used to judge the existence of layer interface simply.The fourth part analyses the current distribution characteristics of the directional electromagnetic propagation resistivity logging, and researches the relationships between logging response and the current distribution characteristics. By changing the formation conductivity contrast ratio, the position of the source in formation, and the eccentricity of tools in the wellhole, the results show that: when the tool is centric in the wellhole, the current density curve is axisymmetrically and uniformly distributed closed concentric elliptical ring; when the tool is eccentric in the wellhole, the current curve is asymmetric, and with the increase of eccentricity, a side of the current curve is closer, and the other side of the current curve is sparser. When the tool is close to the wellhole boundary, the refraction of the electrical current appears on the wellhole wall, which makes the current distribution curve irregular. The change of invasion radius affects slightly on current flow. If the shoulder exists, with the change of formation conductivity contrast ratio, it will generates different degrees of reflection and refraction on the layer interface when the tool is in the center of the target layer, near the layer surface of formation and shoulder, or in the shoulder. Refraction phenomenon happens when the current curve passes through the stratigraphic at a certain angle. And Reflection phenomenon happens when the incident angle or the formation conductivity contrast ratio is greater.The research on the response characteristics of the directional electromagnetic propagation resistivity logging has important theoretical and practical significance for independently developing the directional electromagnetic propagation resistivity logging tools.