A method for determining pore size distribution of rocks is provided. Capillary pressure measurements on rock cores are analyzed to determine a pore size distribution, with smaller pores requiring greater capillary pressure to relinquish contained fluid. Large pores with rough surfaces introduce inaccuracies in determining the pore size distribution. Embodiments of the invention correct the rough surface induced inaccuracies by measuring the shift in NMR T2 distribution from full saturation to the current state of desaturation and subtracting the T2 contributions in the desaturated state that have smaller T2 values (i.e., smaller transverse relaxation time) than the smallest T2 values (i.e., shortest transverse relaxation time) in the saturated distribution.

A method of determining absolute permeability in carbonates without upscaling computations includes performing a nuclear magnetic resonance (NMR) analysis and a mercury-injection capillary-pressure (MICP) analysis on at least three samples from carbonate rock of a set of representative regions to determine an experimental permeability, where each of the representative regions have properties related to the porosity and pore-throat size of the carbonate rock. A series of low resolution X-ray scans and a series of high resolution X-ray scans are performed on the same three samples of the carbonate rock of the set of representative regions. Permeability simulations are performed on the same three samples of the carbonate rock of the set of representative regions to determine a computed permeability. The experimental permeability and the computed permeability are then compared to provide computationally manageable and reasonable estimates of the absolute permeability of the carbonate rock.

Some implementations of the present disclosure provide a method that include: accessing a plurality of measurement logs taken from more than one well locations of a reservoir, wherein the plurality of measurement logs encode, for each well location, a plurality of parameters; based on applying a petrophysical model to the plurality of measurement logs, determining the plurality of parameters; based on a portion of the plurality of parameters, calculating a compressional formation slowness and a shear formation slowness; and predicting a fluid type at the more than one well locations of the reservoir based on combining the compressional formation slowness and the shear formation slowness with at least one of the plurality of parameters.

A method for nuclear magnetic resonance (NMR) logging is disclosed that pulses, using a quadrature antenna of an NMR logging tool in a borehole, a circularly polarized (CP) signal into a formation surrounding the borehole. The method also pulses, using the quadrature antenna, a reverse circularly polarized (RCP) signal into the formation. A sensor of the NMR logging tool detects a first NMR signal from the formation in response to the RCP pulses and a second NMR signal from the formation in response to the CP pulses. A correct transverse magnetization value is then recovered based, at least in part, on the first NMR signal and the second NMR signal.

A method for establishing mathematical model of relationship between spontaneous imbibition volume and time of porous medium includes sample pretreatment, fully-saturation and centrifugal experiments and NMR T.sub.2 measurement. First, two rock core samples of predetermined size are selected for cleaning and drying. The first rock sample is vacuumed and injected with water to obtain a saturated sample for NMR T.sub.2 measurement. Then, spontaneous imbibition experiment is conducted on another sample, and T.sub.2 measurements are conducted to obtain the water distribution and migration characteristics during the imbibition process. Next, the calculation of the imbibition permeability, average capillary pressure and surface relaxivity are conducted based on the NMR data obtained from two samples. Finally, substitute these parameters into the Handy relationship to obtain a new NMR-based mathematical spontaneous imbibition model.

A method and system for transmitting an electromagnetic (EM) signal in a wellbore to improve an open loop system. The method comprises measuring a parameter indicative of a property of a transmitter using a sensor in the wellbore and generating an input signal for the transmitter based at least in part on the measured parameter to correct distortions exhibited by the output signal of the transmitter. The method comprises also comprises applying the input signal to the transmitter to transmit the EM signal corrected for distortions. The system comprises an antenna, a transmitter, a sensor, and a controller. The controller is configured and operable to generate an input signal for the transmitter based at least in part on the measured parameter to correct distortions exhibited by an output signal of the transmitter; and apply the input signal to the transmitter to transmit the EM signal corrected for the distortions.

A method (and corresponding system) that characterizes a porous rock sample is provided, which involves subjecting the porous rock sample to an applied experimental pressure where a first fluid that saturates the porous rock sample is displaced by a second fluid, and subsequently applying an NMR pulse sequence to the rock sample, detecting resulting NMR signals, and generating and storing NMR data representative of the detected NMR signals. The application of experimental pressure and NMR measurements can be repeated over varying applied experimental pressure to obtain NMR data associated with varying applied experimental pressure values. The NMR data can be processed using inversion to obtain a probability distribution function of capillary pressure values as a function of NMR property values. The probability distribution function of capillary pressure values as a function of NMR property values can be processed to determine at least one parameter indicative of the porous rock sample.

Embodiments relate to methods for assessing inaccessible pore volume for polymer flooding. The methods include utilizing nuclear magnetic resonance to monitor polymer-based fluid displacements into porous media. According to an embodiment, the method includes providing a core sample of a porous medium, determining a total pore volume of the core sample, introducing polymer solutions, obtaining nuclear magnetic resonance relaxation time distributions of water within the core sample, and assessing the inaccessible pore volume.

Systems, methods, and apparatuses for determining pore volume and pore volume compressibility of secondary porosity in rock samples is disclosed. In some implementations, determining a pore volume of a secondary porosity in a rock core sample may include saturating the rock sample with deuterium oxide (D2O) by applying a vacuum to the core sample covered by D2O; centrifuging the saturated rock sample at a selected rotational speed in the presence of a second fluid to displace a portion of the D2O from the rock sample with the second fluid; measuring the rock sample with low-field .sup.1H nuclear magnetic resonance (NMR) to determine a volume of the second fluid within the rock sample; and determining a pore volume associated with a secondary porosity based on the volume of the second fluid within the rock sample.

A method for assessing an optimal acid injection rate in the process of hydrocarbon formation stimulation. The method comprises evaluating an anisotropic diffusion coefficient by pulsed gradient NMR, introduction of a semi-empirical correction based on comparison of the downhole conditions with the library of laboratory experiments where such corrections were measured, extrapolation of the library data to the real downhole conditions. The improved values of the diffusion coefficients are applied in determining wormhole regime conditions that are optimal in terms of acid consumption per a unit of stimulated yield of the hydrocarbon.