A Feasibility Study of Time-Lapse [4D] Seismic Monitoring of Water Injection Recovery Processes

Abstract

Abstract Water injection is the most commonly deployed recovery method in most Chinese oilfields. Efficiently monitoring production behavior in the water injection recovery processes is essential to improving water injection efficiency and enhancing oil recovery. Currently, time-lapse seismic reservoir monitoring(TLSRM) is widely used in reservoir monitoring. However, only the reservoirs whose seismic response changes caused by their internal fluid changes are large enough, compared with seismic noise, are suitable for time-lapse seismic surveys. So it is necessary to do a feasibility study of time-lapse seismic before starting a time-lapse seismic survey. Fluvial and delta facies reservoirs are the primary depositional facies types. In this paper, a numerical reservoir simulator is used to simulate the fluid flows in the water injection recovery process in a fluvial reservoir, and Gassman's equation is used to generate synthetic seismograms corresponding to different recovery time. By analyzing velocity and impedance differences between synthetic seismograms of different production time with reservoir physical parameters, the feasibility of TLSRM of the water injection recovery process of the interested reservoir is studied. Introduction Water injection is the most commonly deployed recovery method in most Chinese oilfields. Production in the water-injection oilfields can be divided into three stages: primary production, stable production and descreasing production stages. Since the reservoir recovery time without water-injection is short, recovery with high water cut is the main stage in the reservoir recovery process. And the main method maintaining production in the high water-cut period is the proper adjustment of oil recovery projects. Efficiently monitoring production behavior in the water injection recovery processes is essential to proper adjustment of recovery projects, improving water injection efficiency and enhancing oil recovery. Both fluid production and injection in the recovery processes will result in changes of reservoir physical properties which, in turn, lead to changes of the associated seismic properties and responses. Through analysis and comparison of seismic data repeatedly acquired at different time at the same place, time-lapse seismic can visually indicate the changes of reservoir physical properties in the recovery processes, realizing monitoring of dynamical behavior of recovery processes. However, only the reservoirs whose seismic response changes caused by their internal fluid changes are large enough, compared with seismic noise, are suitable for time-lapse seismic surveys. So it is necessary to do a feasibility study of TLSRM before starting a time-lapse seismic survey.