Research On Preprocessing Method Of Through Casing Resistivity Logging Data

With the development of innovative electronics in the past decades, formation resistivity logging through casing is an emerging technology, which offers accurate and reliable measurement of formation resistivity in cased well with metal casing pipe. The new logging technology has broken the restraints from metal casing pipe in formation resistivity measurement for a long time. It has a deep radial investigation depth, can be used in formation with low porosity and low water salinity. In addition to monitoring reservoir and indentifying bypassed pay in old wells, the cased-hole formation resistivity logging provides a resistivity measurement process in high-risk wells where openhole loggings cannot be run because of borehole conditions or when tool failure prevents successful data acquisition. The technology has been successfully used to extend the economic life of well, to produce hydrocarbons from zones that would otherwise have been overlooked, and to monitor water floods better. What’s more, it is also a potential approach to further discusses questionable oil and gas reservoirs in new exploration wells cemented by steel casing. In Chinese oil fields, the cased-hole formation resistivity logging service was first afforded by Schlumberger Company with its tool called CHFR in2001. Then, Russian cased-hole formation resistivity logging tool, ECOS-31-7, was introduced in2006. Following that, many organizations start to develop this kind of resistivity logging tools. Currently, there are so many research reports on cased-hole formation resistivity logging’s environment corrections, analysis for tools’ field testes, data interpretations and implications at home and abroad. However, papers about data preprocessing methods are rare. Since, a study on the preprocessing method of cased-hole formation resistivity logging data is conducted in this thesis.In order to get formation resistivity, the cased-hole formation resistivity logging tool has to receive feeble current signal, called leakage current, which leak into formation through metal casing. For noise signal is much greater than the leakage current while working in moving up, the cased-hole formation resistivity logging tool adopts the strategy of point measurement. It is to say that the tool measure formation resistivity in a static position, without moving. There would be three times measurement in one station in generally, or even more. Furthermore, in order to save continuous logging time in complex circumstances, depth interval between adjacent stations is usually0.5m, while it is0.3m in target layers and1m in non-target zones. Therefore, compared to conventional logging data, the values of formation resistivity logging through casing are discrete, and the measurement depth interval is different. There might be depth discrepancy also. To be used in combination with other logging data, the cased-hole formation resistivity logging data are must be preprocessed to be single-valued, tighten and equal depth interval, and non depth error.According to the characteristics of the raw data from through-casing formation resistivity logging, a preprocessing method is proposed in this paper, including data choice, data interpolation and depth correction. Firstly, the data choice method which is based on Grubbs Test, one of procedures for detecting outliers in samples, can automatically check the resistivity measurement values one by one, forming data with one optimal value in each station. Secondly, the data interpolation method is based on cubic spline interpolation and parabola interpolation. Through-casing formation resistivity curve with equal depth interval,0.125m, will be generated in this section. Thirdly, the depth correction which is based on cross-correlation could automatically correct the depth error of through-casing formation resistivity curve. The results demonstrate that the proposed method is feasible and effective.With the aid of Software Development Kit (SDK) of Formation Oil&Gas Reservoir Well-Logging Analysis&Research&Development (FORWARD), a corresponding through-casing formation resistivity logging data preprocessing module has been drawled up at last. Above all, the preprocessing module which includes four functions, data loading, data choice, data interpolation and depth correction, has been hooked into FORWARD. The data loading function can draw logging data from TXT files, and write them into WIS files in FORWARD. Consequently, a perfect preprocessing technology of through-casing formation resistivity logging is established and developed to realize these courses and methods, which runs automatically to increase work efficiency.