Monitoring reservoir compaction from subsidence and time‐lapse time shifts in the Dan field

Author(s):  
P. J. Hatchell ◽  
O. Jorgensen ◽  
L. Gommesen ◽  
J. Stammeijer
2021 ◽  
Vol 40 (12) ◽  
pp. 931-935
Author(s):  
Paulo Fernando Villafañe Garcia ◽  
Diogo Folador Rossi ◽  
Antonio Claudio Soares ◽  
Francisco Henriques Ferreira ◽  
Josenilda do Nascimento Lonardelli

The time of flight of a plane wavefront generated from an acoustic pulse is expected to decrease when the medium length between the wave emitter and receiver is shortened. This simple idea is extrapolated to the case of reservoir compaction in order to obtain a geophysical parameter R (dilation factor) that relates the rock deformation to the variation of time of flight (also called time-lapse time shift in 4D seismics) or acoustic velocity of a plane wave propagating in the same direction of deformation. Interpretation of a few laboratory compressive tests with simultaneous ultrasonic acquisition, performed on oil-saturated calcarenite samples, are presented and discussed. The samples were subjected to several stress regimes and simultaneous ultrasonic acquisitions. Despite the formerly ultrasonic acquisition rate limitations, it was possible to obtain R values for various lateral-vertical stress ratios for each sample's linear and nonlinear stress-strain trends.


Geophysics ◽  
2009 ◽  
Vol 74 (1) ◽  
pp. D25-D36 ◽  
Author(s):  
Rodrigo Felício Fuck ◽  
Andrey Bakulin ◽  
Ilya Tsvankin

Time-lapse traveltime shifts of reflection events recorded above hydrocarbon reservoirs can be used to monitor production-related compaction and pore-pressure changes. Existing methodology, however, is limited to zero-offset rays and cannot be applied to traveltime shifts measured on prestack seismic data. We give an analytic 3D description of stress-related traveltime shifts for rays propagating along arbitrary trajectories in heterogeneous anisotropic media. The nonlinear theory of elasticity helps to express the velocity changes in and around the reservoir through the excess stresses associated with reservoir compaction. Because this stress-induced velocity field is both heterogeneous and anisotropic, it should be studied using prestack traveltimes or amplitudes. Then we obtain the traveltime shifts by first-order perturbation of traveltimes that accounts not only for the velocity changes but also for 3D deformation of reflectors. The resulting closed-form expression can be used efficiently for numerical modeling of traveltime shifts and, ultimately, for reconstructing the stress distribution around compacting reservoirs. The analytic results are applied to a 2D model of a compacting rectangular reservoir embedded in an initially homogeneous and isotropic medium. The computed velocity changes around the reservoir are caused primarily by deviatoric stresses and produce a transversely isotropic medium with a variable orientation of the symmetry axis and substantial values of the Thomsen parameters [Formula: see text] and [Formula: see text]. The offset dependence of the traveltime shifts should play a crucial role in estimating the anisotropy parameters and compaction-related deviatoric stress components.


Geophysics ◽  
2020 ◽  
Vol 85 (1) ◽  
pp. B9-B21
Author(s):  
Filipe Borges ◽  
Martin Landrø ◽  
Kenneth Duffaut

On 7 May 2001, a seismic event occurred in the southern North Sea in the vicinity of the Ekofisk platform area. Analysis of seismological recordings of this event indicated that the epicenter is likely within the northern part of the field and its hypocenter lies in the shallow sedimentary layer. Further investigation in this same area revealed a small seabed uplift and identified an unintentional water injection in the overburden. The injection presumably caused the seabed uplift in addition to stress changes in the overburden. To better understand the consequences of this water injection, we analyze marine seismic data acquired before and after the seismological event. The 4D analysis reveals a clear traveltime shift close to the injection well, as well as a weak amplitude difference. We find that these measured time shifts correspond reasonably well with modeled time shifts based on a simple geomechanical model. The modeling also correlates well with the observed bathymetry changes at the seabed and with global positioning system measurements at the platforms. Although no explicit amplitude sign of the seismic event could be detected in the seismic data, the modeled stress changes, combined with the effect of decades of production-induced reservoir compaction, suggest a source mechanism for the far-field seismological recordings of the May 7th event.


2021 ◽  
Vol 40 (1) ◽  
pp. 45-51
Author(s):  
Rachid Rahmoune ◽  
Mohammed Sulaimani ◽  
Jan Stammeijer ◽  
Saif Azri ◽  
Roeland van Gilst ◽  
...  

Time-lapse interferometric synthetic aperture radar (InSAR) remote sensing methods of surface deformation have proven their use in desert environments. The data are acquired frequently without the need to send personnel or equipment into the field. The quality and accuracy of the data is very high. The spatial resolution of the data is excellent and matches that of surface seismic data. These characteristics make the data well suited for a variety of time-lapse monitoring tasks. In this study, we describe the accuracy of the InSAR technique relative to other measurements such as the global positioning system and precise leveling (acquired at known stable locations). We illustrate two case studies of differing natures. In one case, gas production leads to reservoir compaction, which is tracked as surface subsidence with time using frequent InSAR data. The results are used to map zones of increased deformation and identify areas with localized changes. These insights are being used to influence decisions on new wells and well interventions, to provide support for management of facility integrity, and to advise building code and material selection that can withstand the expected rate of deformation. The second case of a shallow steam flood illustrates the use of InSAR data to identify areas of surface uplift following thermal expansion of the reservoir. These data are also used to support the monitoring of the steam chamber growth and confinement in the reservoir. The information from InSAR will become more valuable for reservoir management when the steam chamber matures and conventional downhole data acquisition consequently becomes challenging. In summary, oil and gas fields located in arid environments lend themselves well to remote sensing using the InSAR technique because (1) they are sizeable (from tens to hundreds of square kilometers); (2) they are free from vegetation, snow cover, and most atmospheric distortions, although cloud and pollution can affect the data quality; and (3) they benefit from highly repeatable long-term regular monitoring.


Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. O35-O43 ◽  
Author(s):  
Hossein Mehdi Zadeh ◽  
Martin Landrø

Studying time-lapse time shifts for refracted events is a complementary method to conventional 4D analysis. Especially for detecting changes in relatively shallow subsurface layers, we find that this method has potential. By studying data associated with an old underground blowout, we find consistent time shifts of up to 4 ms when comparing a base survey that was acquired before the underground blowout with a monitor survey acquired 20 months after the blowout. These time shifts are interpreted as caused by shallow gas migration. The 4D refraction time shifts are estimated by a standard windowed crosscorrelation technique. Observed time shifts are compared with a simple synthetic modeling to find the possible property and location of the anomaly. The synthetic result was qualitatively matched with real data. We believe that more quantitative matches can obtained when the method is combined with full waveform inversions. Time-lapse refraction analysis has some clear limitations, for instance, the presence of refracted events, which requires a positive velocity contrast for the interface to be studied. Another limitation is that for deeper events, the signal from shallower refractions and noise associated with the water layer will distort the 4D time shifts. However, we found that these results demonstrate the potential of refraction time shifts as a complementary 4D analysis technique. We believe that the method has a significant potential for quantitative 4D interpretation.


2007 ◽  
Vol 26 (5) ◽  
pp. 655-662 ◽  
Author(s):  
Keith Hawkins ◽  
Sharon Howe ◽  
Steve Hollingworth ◽  
Graham Conroy ◽  
Lotfi Ben-Brahim ◽  
...  

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