Monitoring a Water Flood of Moderate Saturation Changes with Crosswell Electromagnetics (EM): A Case Study from Dom Joao Brazil
Michael Wilt, Ping Zhang, Jorge Maeki, Paulo Netto, Jorge Luiz Sena de Queiroz, Jaciara B. Santos, Valterlene de Oliveira · 2012
Pattern water flooding has recently been pilot tested at the Dom Joao oil field in northern Brazil to improve recovery over the earlier peripheral flooding. The conformance and sweep of the injected water has been monitored over several years using well logs and crosswell EM and the small pilot features fiberglass cased injection wells which are also used for well based and crosswell monitoring using inductive measurements. Baseline crosswell EM data were collected in 2008, prior to initiation of water flooding in 2009. Time lapse crosswell EM and induction logging data collected in 2011 were used to image the water saturation changes between wells. After 2.5 years of flooding, repeated logs indicate that the resistivity has decreased from 12-15 ohm-m to 6-8 ohm-m in some intervals and less in others; this is less than half of the expected change and it is likely due to poor conformance. Tracking this small formation resistivity anomaly has proved challenging for the crosswell EM program, requiring high accuracy data collection and precision tool positioning to recover the 3%-5% field anomalies. Fortunately, benign field conditions and a newly developed field system have provided two remarkable data sets in which the data in non-flooded (i.e. shale) intervals repeat to 1% or less and the small anomalies recovered are imaged with some confidence. The crosswell results have provided an image consistent with the logs showing a low resistivity plume around each injector. The plume typically progresses 50-70m from each injector, and mainly in the upper parts of the reservoir. This suggests that the flooding is progressing slowly and that much of the injected water is traveling to producers in already swept intervals.