Integration Of Wireline Resistivity Data With Dual Depth Of Investigation 2-Mhz MWD Resistivity Data

Dual depth resistivity measurements while drilling (MWD) provide high quality logs which may be integrated with their wireline counterparts. This integration exploits the advantage of measurements recorded both early and late in the invasion process and retains the characteristic strengths of each technology. Dual depth 2-MHz resistivity data acquired while drilling provide the first look at the formation. If potential zones of interest are encountered, a full suite of wireline logs, often including a dual induction and microresistivity, are run to fully evaluate the show. Unfortunately, direct comparison of the wireline resistivities to the MWD resistivities is complicated by the fact that the vertical and radial resolutions of the two devices are different. In particular, the responses of 2-MHz resistivity logs vary with formation conductivity. In high conductivity zones they have very good vertical resolutions and shallow depths of investigation, while in lower conductivity zones the vertical resolution becomes poorer and the depth of investigation increases. Two dimensional field maps and radial and vertical response functions are used to analyze these responses, and the results are corroborated with field log examples from a variety of environments and resistivity ranges. The wireline and the MWD resistivity data may be integrated for a variety of purposes including invasion monitoring and log quality assessment. Since the wireline resistivity log is run some time after the zone is drilled and logged by the 2-MHz tool, the results of the invasion process impose certain advantages and limitations on each of the two logs. The MWD dual resistivity may be used to determine Rt and detect early time (spurt) invasion. The wireline resistivity is run after days to weeks of invasion, so it may be difficult to determine Rt. On the other hand, wireline logs provide Rxo for moved oil analysis and an indication of the resistivity profile.