Formation Resistivity Measurements Through Metal Casing At The Mwx-2 Well In Rifle, Colorado

A second logging instrument was designed and built by Para Magnetic Logging, Inc. (PML) to measure the resistivity of geological formations in steel cased wells. In principle, the new logging tool functions like a Laterolog 3 or guarded-electrode tool, but performs measurements in a cased well. Previous measurements made in a research well with a first logging instrument demonstrated the feasibility of the concept. The second logging instrument has demonstrated improved vertical resolution, faster (although still stationary) measurements, and more accurate results than with the first logging instrument. The data obtained to date from the first and second logging instruments show that the methods of analysis published in earlier patents produce logs that agree fairly well with both induction and laterolog open-hole measurements. The data interpretation method uses the single Calibration Constant K and simple mathematics to generate wellsite logs. An approximate algebraic formula shows that K is largely a function of electrode spacing and casing radius. The favorable comparison of these cased-hole resistivity logs with standard open-hole resistivity logs suggests an application of the method to monitor water saturation behind pipe. Two successful tests were performed using this second logging instrument. The first test was performed in a shallow test well drilled in Woodinville, Washington specifically for the purpose of verifying the measurement and comparing the data to open-hole Dual Laterolog and Dual Induction logs. The second test was in the deep MWX-2 well located near Rifle, Colorado. In both wells the cased-hole resistivity compares favorably with open-hole deep induction logs. In many zones the cased-hole apparent resistivity seems to be a better approximation of true resistivity than the deep induction log.