Monitoring Oil/Water Fronts by Direct Measurement (includes associated papers 23943 and 24103 )
- K. Neil (Scientific Software-Intercomp (U.K.) Ltd.) | B. Dunlop (Scientific Software-Intercomp (U.K.) Ltd.) | Geoffrey A. King (Geophysical Service Inc.) | E. Allen Breitenbach (Scientific Software-Intercomp Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 1991
- Document Type
- Journal Paper
- 596 - 602
- 1991. Society of Petroleum Engineers
- 2.4.3 Sand/Solids Control, 5.4.1 Waterflooding, 5.1.8 Seismic Modelling, 4.5 Offshore Facilities and Subsea Systems, 4.4.2 SCADA, 5.4.2 Gas Injection Methods, 5.5 Reservoir Simulation, 1.2.3 Rock properties, 4.6 Natural Gas, 7.2.2 Risk Management Systems, 4.1.5 Processing Equipment, 3.3.1 Production Logging, 5.2 Reservoir Fluid Dynamics, 5.5.8 History Matching, 4.2 Pipelines, Flowlines and Risers, 4.2.2 Pipeline Transient Behavior, 5.6.4 Drillstem/Well Testing, 3.3 Well & Reservoir Surveillance and Monitoring, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.5.7 Streamline Simulation, 4.1.2 Separation and Treating, 5.1.5 Geologic Modeling, 5.6.1 Open hole/cased hole log analysis, 5.4.6 Thermal Methods, 5.2.1 Phase Behavior and PVT Measurements, 5.1 Reservoir Characterisation
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Summary. A monitoring technique that locates moving reservoir fluids by taking the difference between successive seismic surveys is described. Field measurements are provided by repeated surface-seismic-reflection surveys of limited extent. The seismic measurements are processed to minimize noise and to derive the difference between successive surveys. All acoustic, production, and reservoir data are then integrated by reservoir simulation to define fluid interfaces and volumes. The simulation model provides improved performance predictions. The seismic process has been validated in a field under waterflood. Field-trial results are discussed.
Direct measurement of the position of reservoir fluids during production has great potential for improving recovery because it provides advance warning of changes in production behavior that may be used to prolong well life, or to place new wells more effectively. Knowledge of fluid movement in the reservoir is a key to enhanced production management and determines the quality of performance predictions. Currently, wells provide most of the data available during production. Fluid breakthrough at a well, however, usually signals a decline in the well's production rate. Reliable advance knowledge of the locations of fluid interfaces away from wells would allow remedial actions to be taken to extend the economic lives of these wells. This paper describes a monitoring technique that uses repeated seismic surveys to detect saturation changes at locations distant from wells. The monitoring technique integrates the data currently used for prediction of reservoir behavior with measurements made by differencing repeated surface-seismic-reflection surveys. The continuity of seismic information along cross sections is integrated with the 3D coverage provided by simulation. This creates a field model in which the fluid locations can be verified by direct measurement. Repeated surveys and simulations provide feedback that refines the accuracy of the field model. Simulation then provides more reliable predictions of future field behavior.
The technique is novel because it systematically integrates production data gathering-seismic and all available engineering data-to produce a verified field model. The use of software to integrate the engineering and seismic measurements encourages joint contributions from many disciplines.
Surface seismic monitoring of water/oil displacements has not been reported in the literature. A number of authors have reported the use of seismic for monitoring EOR processes, in some cases with multiple surveys. Greaves and Fulp reported use of multiple 3D surveys to track the effects of a combustion pilot in Texas. Alderman et al., Pullin et al., and Singhal and Card reported on combustion and steamflood monitoring in the Athabasca tar sands of Alberta, Canada. Lawyer and Henley reported the successful monitoring of gas movements in the case of a gas cap and of injected CO2, respectively.
Theoretical and experimental studies on the petrophysical parameters suggest that seismic monitoring can identify water/oil displacements. Nur and Wang and Tosaya et al. provided experimental results describing the acoustic velocities of compressional (P) waves in both pure hydrocarbons and natural crude oils over a range of pressures and GOR's. Surprisingly large changes in acoustic velocity were exhibited with variations of temperature, pressure, and dissolved gas content. Rafipour examined the variation of P-wave velocity at different fluid saturations in clastic core samples and noted the significant change in seismic response that may be expected.
Seismic monitoring requires that a number of variations be made to the conventional seismic data-gathering scheme. These variations result from the need for good amplitude resolution and repeatability between measurements made at different times. Processing is also altered because improvement of the signal-to-noise ratio from the initial seismic survey, which is used as a baseline, is achieved by summation over multiple surveys in areas of the field that are unaffected by saturation changes.
In this paper, seismic monitoring is described and validated through application in a waterflood in a field producing onshore from a thin shaly sand reservoir buried at 1,850 ft [564 m] subsurface. Results are extended in a theoretical discussion to show that the technique may be applied to reservoirs of varying thicknesses and fluid contents and at a wide range of depths in most lithological environments.
Reservoir monitoring, as presented here, is a complete technique for gathering and analyzing data during production. Its aim is to provide the information necessary to make informed production-management decision.
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