This disclosure describes systems and methods to predict viscosity of heavy oil in a geological formation, even when the geological formation also contains water such as clay-bound water, using a downhole nuclear magnetic resonance (NMR) tool. The downhole NMR tools may obtain responses include distributions of a first relaxation time T1, a second relaxation time T2, or diffusion, or a combination of these. The responses of the NMR measurements that are due to water are separated from the responses of the NMR measurements that are due to heavy oil. The responses of the NMR measurements due to heavy oil are then related to likely values of viscosity of the heavy oil based on empirical or simulated measurements.

Methods and systems are provided that enable logging while drilling NMR measurements to be made with magnets placed outside of the drill collar and magnetically permeable members to control the magnetic field gradient. A set of magnets can be disposed on and/or embedded on a drill collar, with an antenna disposed axially therebetween. Alternatively, a set of magnets and an antenna disposed therebetween can be disposed on a sleeve that is slid onto a recess in a drill collar. Additionally, a permeable member can be axially positioned between the set of magnets for affecting the depth of investigation.

Methods and systems are provided that enable logging while drilling NMR measurements to be made with magnets placed outside of the drill collar and magnetically permeable members to control the magnetic field gradient. A set of magnets can be disposed on and/or embedded on a drill collar, with an antenna disposed axially therebetween. Alternatively, a set of magnets and an antenna disposed therebetween can be disposed on a sleeve that is slid onto a recess in a drill collar. Additionally, a permeable member can be axially positioned between the set of magnets for affecting the depth of investigation.

An embodiment of a nuclear magnetic resonance (NMR) apparatus for estimating properties of an earth formation includes an NMR measurement device including a transmitting assembly configured to emit a pulse sequence and a receiving assembly configured to detect an echo train based on the pulse sequence, and a processor. The processor is configured to perform receiving input parameters including an axial speed of the NMR measurement device and a T.sub.1 value associated with a selected formation fluid, analyzing polarization data associated with the T.sub.1 value, the polarization data describing a dependency between polarization and axial speed, determining a wait time for the pulse sequence based on the polarization data, applying the pulse sequence with the determined wait time to the transmitting assembly, and estimating a property of the earth formation based on the echo train detected by the receiving assembly in response to the pulse sequence.

An embodiment of a nuclear magnetic resonance (NMR) apparatus for estimating properties of an earth formation includes an NMR measurement device including a transmitting assembly configured to emit a pulse sequence and a receiving assembly configured to detect an echo train based on the pulse sequence, and a processor. The processor is configured to perform receiving input parameters including an axial speed of the NMR measurement device and a T.sub.1 value associated with a selected formation fluid, analyzing polarization data associated with the T.sub.1 value, the polarization data describing a dependency between polarization and axial speed, determining a wait time for the pulse sequence based on the polarization data, applying the pulse sequence with the determined wait time to the transmitting assembly, and estimating a property of the earth formation based on the echo train detected by the receiving assembly in response to the pulse sequence.

In some aspects of what is described here, a downhole nuclear magnetic resonance (NMR) logging tool can obtain NMR data from a subterranean region. The NMR logging tool includes a magnet assembly operable to produce a static magnetic field in the subterranean region. The NMR logging tool includes an antenna system having a first radio-frequency (RF) antenna, a second RF antenna, and a switching system. The switching system can switch the second antenna among operating modes while the NMR logging tool is disposed in a borehole in the subterranean region. The operating modes can include a booster mode, a spoiler mode, and an inactive mode.

In some aspects of what is described here, a downhole nuclear magnetic resonance (NMR) logging tool can obtain NMR data from a subterranean region. The NMR logging tool includes a magnet assembly operable to produce a static magnetic field in the subterranean region. The NMR logging tool includes an antenna system having a first radio-frequency (RF) antenna, a second RF antenna, and a switching system. The switching system can switch the second antenna among operating modes while the NMR logging tool is disposed in a borehole in the subterranean region. The operating modes can include a booster mode, a spoiler mode, and an inactive mode.

The present invention proposes a method for determining diagenetic patterns in carbonate rocks by resonance and photoelectric factor profiles. It refers to an analytical method to individualize two distinct patterns of diagenetic evolution from statistical treatment, a normal evolution pattern with diagenesis acting on the porous system, and an inverse pattern with diagenesis acting on rock particles.

A method for determining diagenetic patterns in carbonate rocks by resonance and photoelectric factor profiles, characterized in that: a) selecting the electrical profiles measured in the well; b) assessing well intervals under the method application conditions; c) calculating the Pearson’s correlation coefficient between the two variables, photoelectric factor and effective porosity of nuclear magnetic resonance; d) choosing the thresholds for classifying the diagenetic patterns based on the r coefficient; e) applying the interval thickness filter to reduce to the sample scale of interest.

The present invention proposes a method for determining diagenetic patterns in carbonate rocks by resonance and photoelectric factor profiles. It refers to an analytical method to individualize two distinct patterns of diagenetic evolution from statistical treatment, a normal evolution pattern with diagenesis acting on the porous system, and an inverse pattern with diagenesis acting on rock particles.

A method for determining diagenetic patterns in carbonate rocks by resonance and photoelectric factor profiles, characterized in that: a) selecting the electrical profiles measured in the well; b) assessing well intervals under the method application conditions; c) calculating the Pearson’s correlation coefficient between the two variables, photoelectric factor and effective porosity of nuclear magnetic resonance; d) choosing the thresholds for classifying the diagenetic patterns based on the r coefficient; e) applying the interval thickness filter to reduce to the sample scale of interest.

A nuclear magnetic resonance apparatus for estimating properties of an earth formation includes a carrier configured to be deployed in a borehole in the earth formation and at least one transmitting assembly disposed in the carrier and configured to generate an oscillating magnetic field in a volume of interest within the earth formation. The apparatus also includes at least one receiving assembly disposed in the carrier and configured to detect a nuclear magnetic resonance (NMR) signal originating in the volume of interest. In this apparatus, the receiving assembly includes at least a first longitudinal region with a loop coil and a butterfly coil, the loop coil central axis being located over a region of the magnet assembly where a static magnetic field is predominantly along an azimuthal direction to the carrier and the butterfly coil being at least partially overlapped with the loop coil to reduce mutual coupling.