 |
| Titel |
Understanding creep in sandstone reservoirs - theoretical deformation mechanism maps for pressure solution in granular materials |
| VerfasserIn |
Suzanne Hangx, Christopher Spiers |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099302
|
| Publikation (Nr.) |
 EGU/EGU2014-15065.pdf |
|
|
|
|
|
| Zusammenfassung |
| Subsurface exploitation of the Earth’s natural resources removes the natural system
from its chemical and physical equilibrium. As such, groundwater extraction and
hydrocarbon production from subsurface reservoirs frequently causes surface subsidence
and induces (micro)seismicity. These effects are not only a problem in onshore
(e.g. Groningen, the Netherlands) and offshore hydrocarbon fields (e.g. Ekofisk,
Norway), but also in urban areas with extensive groundwater pumping (e.g. Venice,
Italy).
It is known that fluid extraction inevitably leads to (poro)elastic compaction of reservoirs,
hence subsidence and occasional fault reactivation, and causes significant technical,
economic and ecological impact. However, such effects often exceed what is expected from
purely elastic reservoir behaviour and may continue long after exploitation has ceased. This is
most likely due to time-dependent compaction, or ‘creep deformation’, of such reservoirs,
driven by the reduction in pore fluid pressure compared with the rock overburden. Given the
societal and ecological impact of surface subsidence, as well as the current interest in
developing geothermal energy and unconventional gas resources in densely populated
areas, there is much need for obtaining better quantitative understanding of creep in
sediments to improve the predictability of the impact of geo-energy and groundwater
production.
The key problem in developing a reliable, quantitative description of the creep behaviour
of sediments, such as sands and sandstones, is that the operative deformation mechanisms are
poorly known and poorly quantified. While grain-scale brittle fracturing plus intergranular
sliding play an important role in the early stages of compaction, these time-independent,
brittle-frictional processes give way to compaction creep on longer time-scales.
Thermally-activated mass transfer processes, like pressure solution, can cause creep via
dissolution of material at stressed grain contacts, grain-boundary diffusion and precipitation
on pore walls.
As a first step to better describe creep in sands and sandstones, we have derived a simple
model for intergranular pressure solution (IPS) within an ordered pack of spherical grains,
employing existing IPS rate models, such as those derived by Renard et al. (1999) and Spiers
et al. (2004). This universal model is able to predict the conditions under which each
of the respective pressure solution serial processes, i.e. diffusion, precipitation or
dissolution, is dominant. In essence, this creates generic deformation mechanism maps for
any granular material. We have used our model to predict the amount and rate of
compaction for sandstone reservoirs, and compared our predictions to known subsidence
rates for reservoirs around the world. This gives a first order-comparison to verify
whether or not IPS is an important mechanism in controlling reservoir compaction. |
|
|
|
|
|
|