Measuring velocity sensitivity to production‐induced strain at the Ekofisk Field using time‐lapse time‐shifts and compaction logs

Janssen, Aaron L.; Smith, Brackin A.; Byerley, Grant

doi:10.1190/1.2370195

Cited by 20 publications

(7 citation statements)

References 6 publications

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“…13b) broadly agree. Maximum Dt is 6 ms and the maximum Dz is 1.5 m. This relationship between time-lapse time shifts and vertical displacement is in broad agreement with observations at Valhall (Hatchell & Bourne 2005) and Ekofisk (Janssen et al 2006). Both maps show fault control of reservoir compaction, where faults clearly act as flow barriers.…”

Section: Compaction Monitoring On the Northern Crestsupporting

confidence: 84%

Applying time-lapse seismic methods to reservoir management and field development planning at South Arne, Danish North Sea

Herwanger¹,

Schiøtt²,

Frederiksen³

et al. 2010

PGC

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At South Arne a highly repeatable time-lapse seismic survey (normalized root-mean-square error or NRMS of less than 0.1) allowed us to reliably monitor reservoir production processes during five years of reservoir depletion. Time-lapse AVO (amplitude v. offset) inversion and rock-physics analysis enables accurate monitoring of fluid pathways. On the crest of the field, water injection results in a heterogeneous sweep of the reservoir, whereby the majority of the injected water intrudes into a highly porous body. This is in contrast to a pre-existing reservoir simulation model predicting a homogeneous sweep. On the SW flank, time-lapse AVO inversion to changes in water saturation DS w reveals that the drainage pattern is fault controlled. Time-lapse seismic data furthermore explain the lack of production from the far end of a horizontal producer (as observed by production logging), by showing that the injected water does not result in the expected pressure support. On the highly porous crest of the reservoir compaction occurs. Time-lapse time shifts in the overburden are used as a measure for compaction and are compared with predictions of reservoir compaction from reservoir geomechanical modelling. In areas where compaction observations and predictions disagree, time-lapse seismic data give the necessary insight to validate, calibrate and update the reservoir geomechanical model. The information contained in time-lapse seismic data can only be fully extracted and used when the reservoir simulation model, the reservoir geomechanical model and the time-lapse seismic inversion models are co-visualized and available in the same software application with one set of coordinates. This allows for easy and reliable investigation of reservoir depletion and gives deeper insight than using reservoir simulation or time-lapse seismic individually.

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Section: Compaction Monitoring On the Northern Crestsupporting

confidence: 84%

Applying time-lapse seismic methods to reservoir management and field development planning at South Arne, Danish North Sea

Herwanger¹,

Schiøtt²,

Frederiksen³

et al. 2010

PGC

View full text Add to dashboard Cite

show abstract

“…Conventional methodologies employ poststack data and compaction-induced vertical stress/strain to estimate time-lapse velocity and volume changes (Hatchell and Bourne, 2005;Janssen et al, 2006;Carcione et al, 2007;Hodgson et al, 2007;Roste, 2007;Staples et al, 2007;De Gennaro et al, 2008). However, migration and stacking of data represents a complex filtering process that can corrupt phase relationships and arrival times.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of compaction-induced multicomponent seismic time shifts to variations in reservoir properties

Smith

Tsvankin

2013

GEOPHYSICS

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Pore-pressure variations inside producing reservoirs result in excess stress and strain that influence the arrival times of reflected waves. Inversion of seismic data for pressure changes requires better understanding of the dependence of compactioninduced time shifts on reservoir pressure reduction. Using geomechanical and full-waveform seismic modeling, we investigate pressure-dependent behavior of P-, S-, and PS-wave time shifts from reflectors located above and below a rectangular reservoir embedded in a homogeneous half-space. Our geomechanical modeling algorithm generates the excess stress/strain field and the stress-induced stiffness tensor as linear functions of reservoir pressure. Analysis of time shifts obtained from full-waveform synthetic data shows that they vary almost linearly with pressure for reflectors above the reservoir, but become nonlinear for reflections from the reservoir or deeper interfaces. Time-shift misfit curves computed with respect to noise-contaminated data from a reference reservoir for a wide range of pressure reductions display well-defined global minima corresponding to the actual pressure. In addition, we evaluate the influence of the reservoir width on time shifts and the possibility of constraining the width using time-lapse data. We also discuss the impact of moderate perturbations in the strain-sensitivity coefficients (i.e., third-order stiffnesses) on time shifts and on the accuracy of pressure inversion. Our feasibility analysis indicates that the most stable pressure estimation from noisy data is provided by multicomponent time shifts from reflectors below the reservoir. For multicompartment reservoirs, time shifts can be accurately modeled by linear superposition of the excess stress/strains computed for the individual compartments.

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“…However, as the saturation signal is more localized around the injectors than the pressure, this helps when evaluating the overall impact on the seismics. It has been observed on similar fields to South Arne that amplitudes, in particular, are known to be small and noisy and lack the ability to detect the dynamic properties of the reservoir (Janssen, Smith and Byerley 2006). In our case, however, the 4D amplitude signature for the Tor formation appears to reveal a well‐developed region of amplitude decrease (or impedance increase) around the producers, consistent with the zone of strain deformation or pressure depletion indicated on the fluid flow and also the geomechanical simulation predictions (Figs 13 and 14).…”

Section: Data Applicationmentioning

confidence: 99%

An estimation method for effective stress changes in a reservoir from 4D seismics data

García

MacBeth

2013

Geophysical Prospecting

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Advances in seismics acquisition and processing and the widespread use of 4D seismics have made available reliable production‐induced subsurface deformation data in the form of overburden time‐shifts. Inversion of these data is now beginning to be used as an aid to the monitoring of a reservoir's effective stress. Past solutions to this inversion problem have relied upon analytic calculations for an unrealistically simplified subsurface, which can lead to uncertainties. To enhance the accuracy of this approach, a method based on transfer functions is proposed in which the function itself is calibrated using numerically generated overburden strain deformation calculated for a small select group of reference sources. This technique proves to be a good compromise between the faster but more accurate history match of the overburden strain using a geomechanical simulator and the slower, less accurate analytic method. Synthetic tests using a coupled geomechanical and fluid flow simulator for the South Arne field confirm the efficacy of the method. Application to measured time‐shifts from observed 4D seismics indicates compartmentalization in the Tor reservoir, more heterogeneity than is currently considered in the simulation model and moderate connectivity with the overlying Ekofisk formation.

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Measuring velocity sensitivity to production‐induced strain at the Ekofisk Field using time‐lapse time‐shifts and compaction logs

Cited by 20 publications

References 6 publications

Applying time-lapse seismic methods to reservoir management and field development planning at South Arne, Danish North Sea

Applying time-lapse seismic methods to reservoir management and field development planning at South Arne, Danish North Sea

Sensitivity of compaction-induced multicomponent seismic time shifts to variations in reservoir properties

An estimation method for effective stress changes in a reservoir from 4D seismics data

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