Temporal and Spatial Variability of Microseismic Events due to Water Flooding: A Case Study from the Tazlau Field (RO)

Enhanced oil recovery is routinely performed by water flooding in the Tazlau field in Eastern Romania. By the end of 2013, a borehole microseismic feasibility study was launched to gain better understanding of the producing reservoir behavior. Two wells were equipped with 8 geophones in approximately 1000 meters depths in two consecutive periods coinciding with the initiation of the injection phase. In the first well, a significant amount of microseismic events (2566) was recorded during 14 monitoring days, in contrast to a very small number of events (54) observed in the second well in the following 14-day period. This significant difference is related to the varying fracture density in the area and, to a lesser degree, to the amount of injected water. In general, event hypocenters can be located within distances of 600 meters from the monitoring well with sufficient accuracy, and their moment magnitudes range from -1.5 to -3.5. Fracture network characterization based on the microseismic pattern is supported by the analysis of fullbore formation imaging. The study provides new insight on potential water paths. We conclude that borehole microseismic monitoring appears as a promising and useful technique for steering water injection.