Quantitative risk assessment applied to pore pressure prediction
AssigneeGeoMechanics International, Inc.
InventorsDaniel Moos, Pavel Peska, Chris Ward
Life of this patent
Estimating the term…
Abstract
Pre-drill pore pressure and fracture gradient predictions obtained from seismic velocity data are used in well design taking into account uncertainties in the velocity estimation and in the models that use the velocities to determine pore pressure. Using geological constraints, limits are established on hydrocarbon column height. It is also possible to predict the relative number of casings required to reach target reservoirs.
Claims27
A method for determining a property of a subsurface region of an earth formation, the method comprising:
- (a) obtaining a velocity of the subsurface region from a seismic survey;
- (b) estimating from the obtained velocity:
- (A) a formation pore pressure of the subsurface region using a density estimated using the velocity and an effective stress of the subsurface region estimated using the velocity, and
- (B) an uncertainty associated with the estimated pore pressure of the subsurface region, said uncertainty depending at least in part on an uncertainty in the obtained velocity;
- and
- (c) using the determined formation pore pressure for establishing a minimum and maximum mud weight used in drilling a borehole in the earth formation based on at least one of:
- (i) the pore pressure of the subsurface region;
- (ii) a strength of a rock constituting the subsurface region;
- (iii) a maximum principal stress in the subsurface region;
- (iv) a minimum principal stress in the subsurface region;
- and
- (v) a collapse pressure that prevents drilling.
A processor configured to determine from a velocity measured using a seismic survey of a subsurface region of an earth formation an estimate of:
- (a) a formation pore pressure of the earth formation using an estimated density derived from the velocity and an estimated effective stress derived from the velocity;
- (b) an uncertainty associated with the estimate of the pore pressure of the subsurface region, the uncertainty depending at least in part on an uncertainty in the velocity;
- and
- (c) conducting additional drilling operations based on the estimated pore pressure and the uncertainty in the estimate of the pore pressure.
A computer readable medium configured for use in drilling operations, the medium comprising instructions that enable a processor to:
- (a) estimate from a velocity obtained from a seismic survey of a subsurface region of an earth formation:
- a formation pore pressure in a reservoir in the earth formation using an estimated density and an effective stress derived from the velocity,
- (b) an uncertainty associated with the estimate of the pore pressure of the subsurface region, said uncertainty depending at least in part on an uncertainty in the velocity, and
- (c) conduct additional drilling operations based on the estimated pore pressure and the estimated uncertainty in the pore pressure.
A method conducting drilling operations in a subsurface region of an earth formation, the method comprising:
- (a) obtaining a velocity of the subsurface region from a seismic survey;
- and
- (b) estimating from the obtained velocity:
- (A) a formation pore pressure of the subsurface region using a density estimated using the velocity and an effective stress of the subsurface region estimated using the velocity, and
- (B) an uncertainty associated with the estimated pore pressure of the subsurface region, said uncertainty depending at least in part on an uncertainty in the obtained velocity;
- and
- (c) completing the borehole by determining a number of casing segments needed to drill to a specified depth within the subsurface region using the estimated pore pressure and the estimated uncertainty in the pore pressure.
Dependencies are inferred from the claim text.