RESERVOIR COMPACTION: Feasible to ignore? When platy fine-grained sediments get deposited originally (even before the commencement of hydrocarbon production in the pay-zone thickness), they tend to get deposited in random orientations; and thereby, providing enough pore space ‘for the brine’ (to start with) and then, ‘for the oil’ (following the drainage resulting from secondary migration upon exceeding the displacement pressure).
As the reservoir pressure declines with production, even though, these randomly oriented sediments get restructured into stacks which tend to provide relatively lesser space for brine and oil, whether the resulting reservoir compaction can be assumed to remain to be insignificant in those reservoirs which have a relatively early abandonment - with the expectation that very tight reservoir compaction remains ruled out as the reservoir pore pressure during its abandonment still remains to be much larger than the atmospheric pressure?
[Note: In case, if a petroleum reservoir is hypothetically allowed to get depleted until the reservoir pressure becomes equal to that of atmospheric pressure, then, very tight reservoir compaction would remain possible - upon losing all the elastic energy stored and when the commencement of gravity drainage starts taking place; and the above argument has not considered the geological details of 'overlying formation'; and the debate is purely based on the geological aspects of reservoir thickness only.]
The above outline of the compaction process in my view ignores a couple of aspects:
1) platy fine - grained deposits ( ie clay rich instead of porous sandstone or porous limestone) is rarely the productive zone in conventional oil reservoirs. Clayey sediments compact differently from sandstone as well as limestone
2) it assumes no effective aquifer drive
Much more importantly from an operational perspective it ignores the possible impact of significant reservoir compaction on for example casing integrity as well as induced surface subsidence
From a practical standpoint, whether to ignore compaction depends on which reservoir parameter has the widest range of uncertainty. To best judge the predictive power of a model or analysis, the uncertainty of each parameter must be evaluated. If the analysis is just a theoretical "thought exercise" where deterministic parameter ranges are assumed, then the dependencies between parameters must still be considered. In this case, the variation in grain size and mineralogy will affect compaction at the micro scale. Perhaps the relevant question actually "Does compaction matter in a homogenous, anisotropic fine-grained deposit?". Best wishes.
1) Almost every sandstone contains clayey cement, which contains capillaries. It is the capillaries that are subject to the greatest compaction in late diagenesis. 2) The development process is not considered in the work.
The question of the nature of the compaction is very important. In particular, it determines the violation of the connection between modern reservoir properties and sedimentogenesis conditions. This should be taken into account when predicting porosity and permeability.
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