Experience of Downhole Microseismic Monitoring of ReservoirWaterflooding in Baitugan Field

摘要

The paper presents the experience of using downhole microseismic monitoring to determine the direction ofworking agent losses while maintaining formation pressure in Baitugan oil field in Orenburg region.Studieswere aimed at history matching and elaboration of the further strategy for formation pressure maintenance(FPM)and field development as a whole.The seismic monitoring method was used in the downhole version,when observations are done from theobservation well located nearby the injection one.For reliable recording of weak microseismic events,highsensitivity receivers were used with 4 sensors per component.A special injection program was developed.Its first stage consisted in optimization of modes that ensure the maximum injection into formation of afluid supplied at the wellhead.During acquisition parameter testing,passive recording of the seismic signal was done at all stages ofinjection during two weeks in various modes,including a short-term stop of injection with subsequentincrease in injection to a maximum injection rate with exceeding the fracture gradient.Fracture growthzones were identified below the target formation.Starting from the second week of recording,fracturepropagations to the overlying formations were observed under increased injection pressure.Based on dataobtained,a three-dimensional map of microseismic events recorded in the formation was created.It wasused for interpretation and allowed to specify geometry of self-induced hydraulic fractures depending oninjection modes.Microseismic mapping of self-induced fractures in injection wells was done in Russia for the firsttime.The results of observations allow to optimize the formation pressure maintenance system throughoptimizing injection modes depending on local fracture gradients and injection shutting off in the zoneswith uncontrolled self-induced fractures that develop under minimum wellhead pressures.The obtaineddata also make it possible to significantly improve quality of history matching for carbonate deposits withreduced formation pressure through determining the injection efficiency.This result directly improves boththe quality of forecast analysis and economic impact of formation pressure maintenance.