The Study On The Borehole Effects Of The Array Laterolog

With the further demand of petroleum exploration and development technology, the studyof the log\ging response in a variety of complex formation gradually becomes a importantresearch direction. The Array Laterolog Logging tool is a new type of lateral logging tool.Compared with dual laterolog response, it can provide many curves with different depths ofinvestigation. It can give the more invaded zone information and more accurate formation trueresistivity. It is more suitable measurement in the thin layer well logging and the permeableformation. This thesis studies borehole effects of a array laterolog tool. The COMSOLsoftware is used to compute the borehole response of the array laterolog. The research resultshave an important theoretical and practical significance to the array laterolog tool design andthe interpretation and evaluation of the logging response.The first part is the numerical calculation method of the laterolog response based onCOMSOL. Research the advantages of using the COMSOL to calculate electrical loggingproblems and electric logging numerical calculation method. Design a general logging model.Solve the grid subdivision of the model. The efficiency and accuracy of the numericalcomputation are improved. In addition, solve how to determine the outer boundary conditions,whether add the infinite element and how to treat the equivalent problems as adding the source.All these made it possible to compute the actual engineering problem.The second part is the basic theory of array laterolog. Tool structure and measuringprinciple of the array lateral logging are analyzed. Mainly researches five working modes. Thefive working modes are the mud and borehole effects detection mode RLA0, the shallowdetection mode RLA1, the middle and shallow detection mode RLA2, the middle and deepexploration mode RLA3, and the deep exploration mode RLA4. Their working principle,apparent resistivity calculation formula and principle diagram of each mode are studiedrespectively. Establish the formation model and the mathematical model which are used tocalculate the laterolog logging borehole response. Deduce the electric potential and apparentresistivity calculation formula of the array which are used to the numerical calculation indifferent working modes.The third part is the numerical calculation method of the array laterolog borehole effects.Establish the center model when the array lateral logging instrument in the center and eccentric model when tool deviates the center. Calculate the effects of borehole diameter, themud resistivity and the tool eccentricity on the logging response. The results show that themud resistivity and hole radius have a seriou effect on shallow depth response. In addition,how to establish a three dimensional array laterolog borehole effect database and eccentricityeffect database is stated.In the part four, the array lateral logging response characteristics in the invadedsurrounding is studied. Calculate the pseudo geometrical factor and the influence of invasionon logging response. The results show that more shallow the tool radial investigation depth,more serious the invasion effect, and the value of apparent resistivity is more deviated fromthe true formation resistivity value. At the same time, the logging response influenced by thechanges of the formation thickness and changes of target formation thickness. The resultsshow that under different working mode, the shoulder influence of the array lateral loggingresponse is different, The change of target formation thickness and shoulder resistivity botheffect the measured value, which reflects the tool resoluton. In addition, the tool constant K isstudied.In the last part, the electric current distribution characteristics of the array laterolog indifferent strata model are studied. Analyze the response mechanism. Formation modelsinclude uniform, without invasion and shoulder, without invasion and with shoulder, etc. Drawthe focusing current line chart in the constant current field. The results show that the electriccurrent line will occur refraction and reflection phenomenon when it through the differentresistivity surfaces. The degree of reflection and refraction is determined by the electriccurrent incidence angle and resistivity ratio of both sides. The distribution features of thecurrent line reveals the array lateral logging response mechanism.