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US 5,965,810 AGranted
Method for determining sedimentary rock pore pressure caused by effective stress unloading
AssigneeBaroid Technology, Inc.
InventorPhilip W. Holbrook
Life of this patent
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AssigneeBaroid Technology, Inc.
InventorPhilip W. Holbrook
Estimating the term…
An improved technique to more accurately calculate pore pressure of sedimentary rock due to subsurface fluid expansion. The technique is built upon a combination of known force balanced in situ loading limb mineralogical stress/strain relationships with locally variable unloading stress/strain relationships. In stress/strain space, the material properties governed loading limb is an upper limit for the many possible unloading limbs. A method for relating these different natural stress/strain paths and applying the correct path to calculate pore fluid pressure from in situ force balance is disclosed. This method preferably calibrated with in situ stress/strain data which allows for a lithologic sealing caprock to be identified and the locally prevailing in situ unloading limb stress/strain relationship to be estimated. The forced balance loading and unloading calibrations are applied to more accurately determine well casing depths using either wireline or real-time measured while drilling petrophysical data. Solidity (1.0--porsity) is the in situ strain parameter of choice which can be measured petrophysically in the borehole. Pore pressure is the fractions of the total external load which is borne by the fluids in the pore space of a sedimentary rock. The solid framework of a granular sedimentary rock bears the force balance remainder of the external confining load as effective stress. Loading and unloading power law linear stress/strain relationships are determined between effective stress and solidity for common sedimentary rocks.
A method for determining pore pressure in a sedimentary rock, comprising the steps of:
A method for predicting a high pressure formation in a well path being drilled in a subsurface formation by calculating pore pressure for the formation as a function of in situ strain at successive depth locations of said well path, said calculating at each of said depth locations comprising the steps of:
A method for predicting a high pressure formation in a borehole being drilled in a subsurface formation by calculating pore pressure for the formation as a function of the stress/strain relationship for said formation at multiple depth locations of said wellbore comprising the steps of:
Dependencies are inferred from the claim text.