Correction method and implementation of thin layers for cased hole resistivity logging tool with double-injection-electrode

With the innovation and development of electronics components,formation resistivity logging through casing is a new emerging logging technology.By receiving feeble signals caused by leakage current from steel casing into around rocks,cased hole formation resistivity tool could measure formation resistivity.It has been shown significant application value in gas-oil prospecting and exploitation.However,when cased hole formation resistivity tool is used to thin reservoir whose thickness is less than spacing of tool ' s electrodes,the measurement is influenced by shoulder bed.There are lots of domestic reservoirs' thickness is less than 1 m,which affect geologic practical results of the new logging technology.One kinds of cased hole formation resistivity tools with doubleinjection-electrode are widely used in domestic oil fields.So this type of tool is research objects in this paper.Simplified model of layers are built,and influences from thickness and resistivity of stratum have been systematically analyzed by numerical simulation based on modified transmission-line theory for this kind of instrument.One perfect kit of thin bed correction charts are built for different spacing of electrodes,such as 1.0 m and 1.1 m.A corresponding computer program has been also drawled up to realize the course and method.Hooked to common logging software,the program could searches the charts automatically end efficiently.It has been tested by wells' logging data in several oilfields.The results demonstrate that the proposed method is feasible and effective to correct the measurement of thin bed.