Dear Sir/Madam,
What exactly drives the fluid flow in a hydrocarbon reservoir - given the expansion and compression of reservoir-fluids and solid-rock-grains?
(A) When there is ONLY a " constant " external over-burden stress - with a "constant" internal pore-fluid pressure - and - in the absence of any production?
(B) When there is ONLY a " constant " external over-burden stress - with a "varying" internal pore-fluid pressure - and - in the absence of any production?
(C) When there is a "variable" external over-burden stress - with a "variable" internal pore pressure - and - in the absence of any production?
(D) case (A) in the presence of hydrocarbon production?
(E) case (B) in the presence of hydrocarbon production?
(F) case (C) in the presence of hydrocarbon production?
We have theories pertaining to the expansion of solid rock grains and for the reduction in bulk volume, which in turn influence the rock compressibility.
(G) What happens to the expansion of reservoir fluids for under-saturated and over-saturated reservoirs?
Any references or replies on the above queries (A) to (G) are highly appreciated.
Thanks in anticipation.
Suresh Kumar.
Pressure is known to drive the fluid flow in a hydrocarbon reservoir with or without production.
You are asking a billion-year question... ;-) but here is a VERY short Primer for you...
EMPLACEMENT: Organic material gets buried gets pressured up and heated up and creates fluid, and at higher temperatures with greater burial, gas. The compression of the rock matrix (increasing overburden pressure during burial), which contains the original organics, squeezes the oil/gas out of the source rock, along a migration pathway through porous rocks and along faults and into pore spaces in the reservoir rocks. If the pores had other fluids, e.g., water, it gets expelled if there is an exit path, and/or, the pores open as the reservoir rock sees an increasing pore pressure from the oil/gas coming in that pushes against the overburden). After cooking of the organics, the path the oil/gas takes is one of the critical factors in the making of an oil and gas reservoir. Others include trap (a place for the fluids/gas to accumulate - in pores and/or fractures, e.g., a dome, anticline against a fault, against salt, etc.), and seal (something to keep the fluids/gas in the trap and not migrate somewhere else (e.g., overlying impermeable rocks like shale or salt)... without a trap, the oil/gas will end up migrating all the way to the surface... forming seeps and the tar/pitch pits of biblical description. "Variability/Constancy" in the over-burden/pore-pressure is what determines, what , where, when and how this all happens.
PRODUCTION: When an oil well is drilled, oil will flow to the surface as it is under pressure compared to the weight of the drilling mud in the borehole. So during drilling, proper mud weight is critical... too low and you get a blow out, too high and the mud fractures and penetrates the rocks and can ruin production from the reservoir. As the oil/gas is produced: (a) compaction of the reservoir occurs to keep the oil flowing, and (b) pressure from the water in the rocks below the reservoir also maintains the reservoir's pressure... this is called the aquifer drive. You need to have a big enough aquifer to drive out the oil, or it will not flow. If the reservoir pressure starts to low, is falls off too low from production, then you have to pump it out, or inject water or other fluids/gases (H2O, CO2, N2, Natural Gas, etc.) at the edges of the reservoir, below the oil/gas you want to produce, to help push it out.
Most any petroleum geology book will describe all this, as well as books covering reservoir engineering for more detail on the production side.
Hope this helps...
Thanks for your time and reply. However, I am looking for an answer which contains the details of associating fluid flow within a hydrocarbon reservoir as a function of (a) energy storage; (b) elasticity (rock compressibility); and (c) the individual contributions on the expansion/compression of water, oil and gas. I am looking at the basics. Thanks.
These are factors that are taken into account in running a reservoir model. Maybe you need to look along those lines? Sorry I can't help more, but I'll keep you in mind. I have a reservoir engineer joining our company in a month or so, I can talk to her.
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