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

摘要

Formation evaluation (FE) of horizontal injectors drilled inrnwater swept reservoirs involves different physicalrnunderstanding of log responses to fluid flow and distributionrnthan that FE of oil producers drilled in dry oil intervals. Inrnreservoirs swept with water, effects of rock electricalrnanisotropy on logging-while-drilling (LWD) apparentrnresistivity measurements (attenuation and phase shift) could bernsignificant. These effects need to be considered in resistivityrnlog interpretation. In this study, LWD resistivity modelingrnwork was conducted to study relationships between truernformation resistivity and LWD tool responses. In situationsrnwhere the time-consuming resistivity modeling/inversion isrnnot available, LWD apparent attenuation is found to be morernrepresentative to true formation resistivity than the apparentrnphase shift resistivity, thus can be used in formation waterrnsaturation estimation.rnAn alternative measurement of formation fluid saturationrnis by pulse neutron (PN) after well completion. Newrntechnologies have been developed to characterize formationrnsaturation through casing, I.e., behind-casing-analysis (BCA)rnwhich includes PN and casedhole resistivity. Logging longrnhorizontal intervals of BCA services is different from loggingrnvertical wells. First of all, the issue of vertical resolution inrnhorizontal wells is not as critical. Secondly, the gravity effectrnon the tool orientation is different. Data quality could also berndifferent when logging long intervals of the casedholernresistivity because the tool requires physical contact betweenrnthe measurement pads and the casing. In this paper, all thesernissues are summarized. The BCA logs are integrated withrnresults of the LWD modeling and production data whilernunderbalanced drilling to provide more accurate formationrnevaluation.