Continuous reservoir modeling updating by integrating experimental data using an ensemble Kalman Filter

The continuous researvoir model updating is widely used to calibrate reservoir simulation models to production data, but many challenges remain. First, few real field data are available to test the new history matching method, and most of the data sets are synthetic cases. Second, computational cost may be high when using non-Gaussian priors or nonlinear models. Third, with large complex models, the simulation runs and history matching method require huge memory allocations. This dissertation achieves a continuous reservoir model updating workflow with a meter-scale , two-phase flow experiment. Both production and seismic data are collected in the experiment. Because the data are high-frequency sequential data with noise, the EnKF method is used to efficiently integrate them. To better understand the problem, scaling analysis is done on the capillary transition zone. Two new dimensionless numbers are introduced-capillary time and capillary length. We found that for different models, if their capillary time and gravity number are equal, the capillary length would be the same. The scaling analysis results help us find a proper flow rate for the sand tank experiment. Two experiments are conducted to test the workflow and the EnKF method. In the first one, both the production and seismic data are collected and analyzed. The production data have large errors in the flow rate and they are integrated to improve reservoir models using EnKF method. The history matching results are in an acceptable range which demonstrate that even if the observation data has large error, the EnKF method still works. In the second experiment, the errors of flow rate are reduced by measuring manually with a graduated cylinder. Because the data quality are much better in the second experiment, the observations can be matched easily

Effects of stress and water saturation on seismic velocity and attenuation in near surface sediments

Seismic investigation in the near-surface is complicated by highly attenuating media, large interparticle stresses, and variable water saturation, so new tools and methodology are necessary to understand the relationships between velocity, attenuation, and physical properties of the propagating media. A new shear wave source is developed for investigation of gas-charged, organic-rich sediments because compressional waves are highly attenuated and currently available sources are inadequate. The new source compares favorably to a traditional hammer impact source, producing a signal with a broader-band of frequencies (30-100Hz cf. 30-60Hz) and signal-to-noise ratios (SNR) equivalent to ~3 stacked hammer blows to the hammer impact source. Ideal source signals must be broadband in frequency, have a high SNR, be consistent, and have precise start times; all traits of the new shear source. A new constitutive model predicting seismic velocity is developed because current models do not include interparticle stresses which are especially important in materials with large cohesive and capillary pressures such as clays. The new proposed methodology calculates elastic moduli of granular matrices in near-surface environments by incorporating an updated definition of total effective stress into Hertz-Mindlin theory and calculates the elastic moduli of granular materials by extending Biot-Gassmann theory to include pressure effects induced by water saturation. As water saturation increases in shallow sediments, theoretically calculated seismic velocities decrease in clay and increase in sand because of the respective interparticle stresses in these media. The proposed model calculates seismic velocities that compare well with measured field velocities from the literature. A field-transferrable lab experiment shows the simultaneous dependence of quality factor (Q) on water saturation and stress in unconsolidated sand. Local Q values (Qint) increase the most with depth (dQ/dz=43 m-1) and stress (dQ/dS=0.0025/Pa) in dry sand and the least in partially saturated sand (dQ/dz=10m-1 and dQ/dS=0.0013/Pa) where attenuation created by local fluid flow reaches a maximum. Expectations for Qint values with depth can be extrapolated from dQ/dS and are bounded by Qint of the dry (QD) and partially saturated (QPS) media (e.g.,QD\u3eQint\u3eQPS). Qint deviations outside this range can be explained by a divergence in effective stress, attenuation mechanism, or lithology

Benchmark hydrogeophysical data from a physical seismic model

Theoretical fluid flow models are used regularly to predict and analyze porous media flow but require verification against natural systems. Seismic monitoring in a controlled laboratory setting at a nominal scale of 1:1000 in the acoustic frequency range can help improve fluid flow models as well as elasto-granular models for uncompacted saturated-unsaturated soils. A mid-scale sand tank allows for many highly repeatable, yet flexible, experimental configurations with different material compositions and pump rates while still capturing phenomena such as patchy saturation, flow fingering, or layering.The tank (~6×9×0.44. m) contains a heterogeneous sand pack (1.52-1.7. phi). In a set of eight benchmark experiments the water table is raised inside the sand body at increments of ~0.05. m. Seismic events (vertical component) are recorded by a pseudowalkaway 64-channel accelerometer array (20. Hz-20. kHz), at 78. kS/s, in 100- scan stacks so as to optimize signal-to-noise ratio. Three screened well sites monitor water depth (+/-3. mm) inside the sand body. Seismic data sets in SEG Y format are publicly downloadable from the internet (http://github.com/cageo/Lorenzo-2012), in order to allow comparisons of different seismic and fluid flow analyses.The capillary fringe does not appear to completely saturate, as expected, because the interpreted compressional-wave velocity values remain so low (\u3c210. m/s). Even at the highest water levels there is no large seismic impedance contrast across the top of the water table to generate a clear reflector.Preliminary results indicate an immediate need for several additional experiments whose data sets will be added to the online database. Future benchmark data sets will grow with a control data set to show conditions in the sand body before water levels rise, and a surface 3D data set. In later experiments, buried sensors will help reduce seismic attenuation effects and in-situ saturation sensors will provide calibration values. © 2012 Elsevier Ltd