Geomechanical stresses from 4D time shifts measured around the depleting Franklin and Elgin reservoirs

Hawkins, Keith; Howe, Sharon; Hollingworth, S.; Conroy, Graham; Ben-Brahim, L.; Tindle, C.; Taylor, N.; Joffroy, G.; Onaisi, A.

doi:10.1190/1.2793061

Cited by 3 publications

(1 citation statement)

References 5 publications

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“…One of the conditions for visible compaction is the significant reduction of pore pressure into a loose or weakly cemented rock, as observed in Groningen field (Mobach and Gussinklo, 1994). Another one is pressure depletion of high pressure high temperature reservoir (HPHT), as observed in Elgin-Franklin field (Hawkins et al, 2007). A further condition for compaction is the chemical interaction between reservoir formation and injected water, as observed in the Ekofisk field (Teufel et al, 1991;Janssen et al, 2006;Guilbot and Smith, 2002) and in the Valhall field the North sea .…”

Section: Scope Of the Thesismentioning

confidence: 99%

Effects of reservoir compaction on seismic and gravity monitoring

Tempone

2011

GEOPHYSICS

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Geophysics publishes abstracts of dissertations and titles of master’s theses both in print and online. Recent graduates are invited to submit their abstracts or titles by completing and submitting the appropriate form found at http://seg.org/dissertationabstracts. Abstracts and titles will be reviewed and accepted or rejected based on their relevance to the readers of Geophysics. Abstracts must be written in English and defended in 2009 or later.

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Section: Scope Of the Thesismentioning

confidence: 99%

Effects of reservoir compaction on seismic and gravity monitoring

Tempone

2011

GEOPHYSICS

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Offset dependence of overburden time‐shifts from ultrasonic data

Bakk

Holt

Bauer

et al. 2020

Geophysical Prospecting

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Depletion or injection into a reservoir implies stress changes and strains in the reservoir and its surroundings. This may lead to measurable time‐shifts for seismic waves propagating in the subsurface. To better understand the offset dependence of time‐shifts in the overburden, we have systematically quantified the time‐shifts of three different overburden shales in controlled laboratory tests. These experiments may be viewed as an analogue to the time‐shifts recorded from seismic field surveys. For a range of different stress paths, defined as the ratio between the horizontal and the vertical stress changes, the changes of the P‐wave velocities in different directions were measured such that the offset dependence of time‐shifts for different stress paths could be studied. The time‐shifts are stress path dependent, which is particularly pronounced at large offsets. For all stress paths, the time‐shifts exhibit a linearly decreasing trend with increasing offset, that is, a negative offset gradient. At zero offset, for which the ray path is normal to the bedding, the time‐shifts are similar for all investigated stress paths. The isotropic stress path is associated with the smallest offset gradient of the time‐shifts. In contrast, the constant‐mean‐stress path shows the largest gradient with a flip in the polarity of the time‐shifts for the largest offsets. The separate contributions from the strain and velocity changes to the time‐shifts were also quantified. The time‐shifts for the isotropic stress path are dominated by the contribution from velocity changes at all offsets. In contrast, the strain contributes significantly to the time‐shifts at small offsets for the constant‐mean‐stress path. This shows that the offset dependence in pre‐stack seismic data may be a key to understand the changes of subsurface stresses, pore pressure and strain upon depletion or injection. To utilize this knowledge from laboratory experiments, calibrated rock physics models and correlations are needed to constrain the seismic time‐shifts and to obtain an adequately updated geological model reflecting the true anisotropic nature of the subsurface. This may have important implications for improved recovery and safety, particularly in mature fields.

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4D gravity response of compacting reservoirs: Analytical approach

2012

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Time-lapse gravity is a technique sensitive to subsurface change in mass and in mass distribution. We attempted to devise a method to predict gravity effects caused by redistribution of subsurface mass induced by reservoir compaction. First, displacements and strains due to compaction were modeled using a geomechanical model. Then, 4D gravity effects were derived from the displacements and the volumetric strains computed in and around the reservoir. A sensitivity study was carried out for geomechanical parameters, such as Poisson’s ratio, as well as for geometrical parameters, such as reservoir radius and depth. Finally, changes in gravity due to compaction were compared to changes induced by reservoir fluid substitution. Given a rigid basement close below a strongly compacting reservoir, our modeling case showed that the deformation itself could give gravity changes comparable to changes caused by reservoir fluid density changes, which are the changes traditionally targeted by gravity monitoring. For a homogeneous subsurface, the compaction gave negligible gravity changes for our modeling case.

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Geomechanical stresses from 4D time shifts measured around the depleting Franklin and Elgin reservoirs

Cited by 3 publications

References 5 publications

Effects of reservoir compaction on seismic and gravity monitoring

Effects of reservoir compaction on seismic and gravity monitoring

Offset dependence of overburden time‐shifts from ultrasonic data

4D gravity response of compacting reservoirs: Analytical approach

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