IMPROVED SHALY SAND INTERPRETATION IN HIGHLY DEVIATED AND HORIZONTAL WELLS USING MULTICOMPONENT INDUCTION LOG DATA

摘要

Significant amounts of hydrocarbon reserves are located in low-resistivity reservoirs that are comprised of thinly laminated sand/shale sequences with hydrocarbon bearing sand laminae. Detection of these reservoirs and accurate characterization of their formation parameters are challenging when using conventional resistivity responses if the laminae are below the vertical resolution of the tool. Thinly laminated sand/shale sequences can exhibit electrical anisotropy with different resistivities parallel and perpendicular to bedding. These resistivities are termed horizontal and vertical resistivities, respectively. Conventional induction devices measure the horizontal resistivity in a well, drilled perpendicular to the bedding and a combination of both horizontal and vertical resistivity in deviated and horizontal wells. From conventional induction log data alone, it is not possible to de-couple horizontal and vertical resistivity. However, the new multicomponent induction logging tool (3DEXT) provides the necessary measurements to derive both horizontal and vertical resistivity in vertical, deviated, and horizontal wells to determine the hydrocarbon saturation of the sand laminae. We logged a prototype tool for the first time in a horizontal producer in the North Sea. The reservoir comprises sections where laminated sand/shale packages of more than 3-ft total thickness commonly occur. These laminated sand/shale intervals can represent levee, crevasse splay or overbank sheet sands in the proximity of deltaic channels, or the lower portion of washover fans in a lagoonal environment. The objectives of this field test were to first obtain reliable resistivities to be verified with other wireline data and external data. The second main objective was then to use these resistivity data to obtain unproved and accurate oil saturation estimates over the laminated sand/shale intervals. The resistivity values from the 3DEX~(TM) are consistent with resistivities obtained by the High Definition Induction Log (HDIL) and LWD data from the 2-MHz Resistivity Navigator Tool (RNT). Over clean and resistive sands, embedded in conductive shales, the 3DEXT yields horizontal and vertical resistivities that are in better agreement with corresponding resistivity data from an adjacent vertical well than both the HDIL focused resistivity data and the RNT inversion results. Over the laminated shaly sand interval the combination of horizontal and vertical 3DEX~(TM) resistivities using a laminar shaly sand evaluation method yielded a 35% increase in total oil volume compared to the standard evaluation applied for this field. Over individual zones within the laminated intervals, the hydrocarbon saturation derived from 3DEX~(TM) data shows an excellent agreement with those obtained from capillary pressure curve data. In addition, the resistivities correlate much better to the shaliness derived from GR/density/neutron logs when compared to an interpretation based on conventional induction data. These improvements in petrophysical interpretation are attributed to the additional resistivity measurements provided by the 3DEX~(TM).