Formation Evaluation of Horizontal Water Injectors Drilled in Thick Carbonate Reservoirs: Behind-Casing-Analysis and LWD Resistivity Modeling

摘要

Formation evaluation (FE) of horizontal injectors drilled in water swept reservoirs involves different physical understanding of log responses to fluid flow and distribution than that FE of oil producers drilled in dry oil intervals. In reservoirs swept with water, effects of rock electrical anisotropy on logging-while-drilling (LWD) apparent resistivity measurements (attenuation and phase shift) could be significant. These effects need to be considered in resistivity log interpretation. In this study, LWD resistivity modeling work was conducted to study relationships between true formation resistivity and LWD tool responses. In situations where the time-consuming resistivity modeling/inversion is not available, LWD apparent attenuation is found to be more representative to true formation resistivity than the apparent phase shift resistivity, thus can be used in formation water saturation estimation. An alternative measurement of formation fluid saturation is by pulse neutron (PN) after well completion. New technologies have been developed to characterize formation saturation through casing, I.e., behind-casing-analysis (BCA) which includes PN and casedhole resistivity. Logging long horizontal intervals of BCA services is different from logging vertical wells. First of all, the issue of vertical resolution in horizontal wells is not as critical. Secondly, the gravity effect on the tool orientation is different. Data quality could also be different when logging long intervals of the casedhole resistivity because the tool requires physical contact between the measurement pads and the casing. In this paper, all these issues are summarized. The BCA logs are integrated with results of the LWD modeling and production data while underbalanced drilling to provide more accurate formation evaluation.