Apparatus and methods for measurement of pore pressure in rock formations through an open, or cemented and/or cased, borehole are described. Such measurements are achieved using the Dynamic Acoustic Elasticity (DAE) method for characterizing nonlinear parameters by perturbing a selected rock formation volume with a High Amplitude, Low Frequency (HALF) acoustic strain wave, and probing this volume using a Low Amplitude, High Frequency (LAHF) acoustic wave. Time reversal techniques may be employed for focusing acoustic energy Into the formation in the vicinity of the pipe or open hole.

The present disclosure describes methods and systems, including computer-implemented methods, computer program products, and computer systems, for determining a mudweight of drilling fluids in a hydrocarbon reservoir. One computer-implemented method includes: receiving pore pressure data of a rock formation in the hydrocarbon reservoir; determining permeability data of fractures of the hydrocarbon reservoir; determining Hoek-Brown failure criterion data; and determining a safe mudweight window based on the pore pressure data of the rock formation, the permeability data of the fractures, and the Hoek-Brown failure criterion data.

A pressure wave is generated within a first well extending into a subterranean formation. A pressure response associated with the pressure wave is detected from a second well extending into the formation. Information is then determined, based on the pressure response in the second well, wherein the information is associated with at least one of the formation and a fracture connected to at least one of the first well and the second well.

Apparatus (10) and methods for measurement of pore pressure in rock formations through a metal borehole casing (32) after a well is cased and cemented, are described. Such measurements may be accomplished by using the Dynamic Acoustic Elasticity (DAE) method for characterizing nonlinear parameters by perturbing a selected rock formation region with a High Amplitude, Low Frequency (HALF) acoustic strain wave, and probing this region using a Low Amplitude, High Frequency (LAHF) acoustic wave (18), (22). Time reversal techniques (36) may be employed for focusing acoustic energy into the formation in the vicinity of the pipe or open hole. The change in wave speed of the probe pulses as the HALF induced strain wave oscillation propagates through the formation, as a function of the induced strain, may be used to determine the nonlinear elastic parameters , , , and A of the pore pressure, from which the pore pressure may be determined in the region of the HALF wave.

The invention relates to a method for modeling a sedimentary basin, said sedimentary basin having undergone a plurality of geological events defining a sequence of states {A.sub.i} of the basin, each of said states extending between two successive geological events, the method comprising the implementation by data processing means (21) of steps of: (a) Obtaining measurements of physical quantities of said basin, which are acquired from sensors (20); (b) For each of said states A.sub.i, constructing a meshed representation of said basin depending on said measurements of physical quantities; (c) For each of said states A.sub.i, and for each cell of said meshed representation, computing an overpressure in the cell at the end of the state A.sub.i by solving an equation of the Darcy equation type;

characterized in that step (c) comprises a prior step (c).0 of verifying that for at least one of said cells the overpressure has changed during the state A.sub.i by more than a first preset threshold, and implementing the rest of step (c) only if this is verified.

A method for estimating in real time the geomechanical properties using drilling data and an accurate drilling model. An initial structural framework and initial distribution of the geomechanical and other rock properties is adjusted in real time by estimating accurately the corrected mechanical specific energy (CMSE), which is then used to estimate the geomechanical and other rock properties. For example, the updated geomechanical model can be used to geosteer the well toward the brittle zones that will achieve the best stimulation when using hydraulic fracturing in unconventional wells.

A pressure wave is generated within a first well extending into a subterranean formation. A pressure response associated with the pressure wave is detected from a second well extending into the formation. Information is then determined, based on the pressure response in the second well, wherein the information is associated with at least one of the formation and a fracture connected to at least one of the first well and the second well.

A method for estimating reservoir quality from a reflection seismic survey includes determining seismic interval velocity (or their inverse, interval transit time ITT) with respect to depth from the reflection seismic survey. A normal compaction trend of the seismic interval velocity with respect to depth is determined. A fractional amount of sand and a fractional amount of shale at at least one depth is determined based on deviation of the seismic interval velocity (or ITT) at the at least one depth from the normal compaction trend.

Apparatus (10) and methods for combining time reversal and elastic nonlinearity of formation materials for qualtitatively probing for over-pressured regions down hole in advance of a well drilling bit, to determine the distance to the over-pressured region, and for accurately measuring pore pressure downhole in a formation, are described. Classical and reciprocal time reversal methods may be utilized to achieve these measurements.

A method is described for seismic imaging including determination of reservoir stresses. The method may include the use of elastic full waveform inversion (FWI), 3.sup.rd-order elasticity, and finite-difference strain calculations. The method may be executed by a computer system.