Mobil Oil Corporation

W D Lyle

John L Fitch

Luke S Gournay

David C Stromswold

L Scott Allen

D Michael Williams

F Fay Osborn

Frank P Leland

Donald M Williams

Joseph Zemanek

A borehole logging tool is lowered into a borehole traversing a subsurface formation and a neutron detector measures the die-away of nuclear radiation in the formation. A model of the die-away of nuclear radiation is produced using exponential terms varying as the sum of borehole, formation and thermal neutron background components. Exponentially weighted moments of both the die-away measurements and die-away model are determined and equated. The equated moments are solved for the ratio of the borehole to formation amplitude components of the measurements. The formation decay constant is determined from at least the formation and thermal neutron background terms of the weighted measurement and model moments. An epithermal neutron lifetime is determined from the formation decay constant. This epithermal neutron lifetime and the amplitude ratio are used by a trained neural network to determine a lifetime correction and an apparent standoff. A standoff corrected lifetime is determined from the epithermal neutron lifetime and the lifetime correction. A porosity log of the formation is produced which is corrected for detector standoff from the borehole wall as a function of the standoff corrected epithermal neutron lifetime calibrated in borehole models of known porosities.

Method and apparatus for producing a porosity log of a subsurface

A deviated borehole penetrating a subsurface formation and intersected by a formation fracture is surveyed with a borehole televiewer acoustic logging system. Relative fracture dip angle and dip direction calculated from such survey with respect to the borehole axis is transformed into a true fracture dip angle and dip direction with respect to the vertical of the earth's coordinate system.

Acoustic logging method for determining the dip angle and dip direction

A gravity gradient logging tool is used to conduct a gravimetry survey of an earth formation. A pair of piezoelectric transducers are located at spaced apart positions within the logging tool. Each transducer is loaded with a known mass and excited electrically so as to vibrate at a characteristic resonant frequency. The period of vibration of each transducer is measured as the logging tool continuously traverses the formation. The difference in the measured periods of vibration is determined as a measure of gravity gradient along the formation.

Gravimetry logging

A borehole logging tool is rotated within a borehole and also advanced along the borehole. A log of the formations surrounding the borehole is recorded. An interval of the borehole intersected by a formation fracture is identified on the recorded log. The fracture dip angle and dip direction are determined from the location of the center of the fracture with respect to the borehole and the peak amplitude and phase angle of the recorded borehole signal at the fracture location.

Method for logging the characteristics of materials forming the walls of

Disclosed is a logging technique wherein measured parameters which are inherently weighted average measurement values are inverse filtered to improve the resolution of the measured values. Higher resolution values of log measurements are obtained from information contained in the measurements themselves, and the response function of a logging tool. Measurement errors due to impulsive noise are detected, located and corrected using innovation data contained in the log measurements.

Method of detecting and correcting impulse noise errors in log data

A borehole gravimetry survey is carried out by making gravity measurements at a plurality of measurement stations along an interval of the borehole. A moving average gradient is determined for gravity measurements taken from consecutive pairs of such measurement stations over the borehole interval. Each moving average gradient is inverse filtered to reduce the effect of the weighted averaging on the gravity measurements, thereby increasing the vertical resolution of the data.

Borehole gravimetry logging

A continuous gravimetry survey is carried out with a gravity logging tool having a column of fluid within the tool. First and second pressure sensors are located at spaced-apart axial positions within an upper portion of the fluid column. Third and fourth pressure sensors are located at spaced-apart axial positions within a lower portion of the fluid column. The outputs from the first and second pressure sensors are differenced to produce a first pressure difference signal. The outputs of the third and fourth pressure sensors are also differenced to produce a second pressure difference signal. The difference between these first and second pressure difference signals is related to the gravity gradient along the earth formation adjacent the fluid column. Such a gravity gradient is a continuously moving gradient that is insensitive to acceleration effects from unsteady motions of the logging tool as it traverses the earth formation during the gravimetry survey.

Continuous gravity gradient logging

Disclosed is a logging technique wherein measured parameters which are inherently weighted average measurement values are inverse filtered to improve the resolution of the measured values. A processing technique is employed, wherein higher resolution values of logged measurements are obtained from information contained in the measurements themselves, and the response function of a logging tool and without emulating a white-noise driven system.

Method of increasing the vertical resolution of well log data

A borehole logging system includes a borehole gravity meter and a resistivity logging tool. A borehole gravity log and a resistivity log are produced over a select depth interval in a borehole. The bulk density of the subsurface formation surrounding the borehole over the select depth interval is measured from the gravity log. The bulk resistivity of the formation surrounding the borehole over the select depth interval is measured from the resistivity log. The bulk density and bulk resistivity measurements are combined to derive a measurement of the residual oil saturation of the subsurface formation surrounding the borehole for the select depth interval.

Method for determining oil saturation in a subsurface formation

A borehole gravimety system employs a pair of pressure transducers for lowering into a borehole along with a borehole gravity meter. The pressure transducers are spaced apart vertically within a pressure sonde for producing a pressure differential measurement of the wellbore fluid. A pressure differential measurement and a gravity reading is taken for each of a plurality of vertical locations within the borehole as the borehole gravimetry system is advanced through the borehole.

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Grapevine, TX, United States of America

W D Lyle