Systems and methods for determining the thermal maturity of a rock formation from isotopic values in gases are provided. Isotope values may be obtained from mud gas isotope logging, vitrinite reflectance equivalence values may be determined from core samples using known techniques. A relationship between vitrinite reflectance equivalence and isotopic values, such as carbon-13 methane values, may be determined. The vitrinite reflectance equivalence may then be determined from isotopic values to determine the thermal maturity of rock formations accessed by drilling additional exploration wells.

Embodiment disclosed herein include systems and methods for azimuthally imaging a borehole, A logging tool having one or more gamma radiation sensors is disposed at a depth position within a borehole, with the one or more gamma radiation sensors positioned to measure gamma radiation within multiple azimuthally offset sectors. The gamma radiation sensors measure gamma radiation at one or more positions within each of the azimuthally offset sectors. A spectral gamma radiation profile is determined for three radioelements at the one or more positions within each of the azimuthally offset sectors based on the gamma radiation measurements. Concentrations of each of the radioelements are determined at the one or more positions based, at least in part, on the spectral gamma radiation profiles, A plurality of color coded points that each encode the combined concentrations of one or more of the radioelements are generated by mapping each of the determined concentrations to an axis point on each of three color coded axes that define a three dimensional display space. The color coded points are rendered in an azimuthal radioelement borehole image.

Embodiment disclosed herein include systems and methods for azimuthally imaging a borehole, A logging tool having one or more gamma radiation sensors is disposed at a depth position within a borehole, with the one or more gamma radiation sensors positioned to measure gamma radiation within multiple azimuthally offset sectors. The gamma radiation sensors measure gamma radiation at one or more positions within each of the azimuthally offset sectors. A spectral gamma radiation profile is determined for three radioelements at the one or more positions within each of the azimuthally offset sectors based on the gamma radiation measurements. Concentrations of each of the radioelements are determined at the one or more positions based, at least in part, on the spectral gamma radiation profiles, A plurality of color coded points that each encode the combined concentrations of one or more of the radioelements are generated by mapping each of the determined concentrations to an axis point on each of three color coded axes that define a three dimensional display space. The color coded points are rendered in an azimuthal radioelement borehole image.

System and methods for calibrating gamma ray tools using blanket field calibrator models is provided. A counting rate of a first gamma ray tool is simulated based on a model of a first blanket calibrator. When it is determined that the simulated counting rate matches a measured counting rate associated with the first gamma ray tool, a tally multiplier and a corresponding material specification for the model of the first blanket calibrator is determined. A counting rate for a second gamma ray tool is simulated based on the tally multiplier and the material specification determined for the model of the first blanket calibrator. A sensitivity factor for the second gamma ray tool is determined based on the simulation. The second gamma ray tool is calibrated according to a nominal blanket activity calculated from the sensitivity factor of the second gamma ray tool.

System and methods for calibrating gamma ray tools using blanket field calibrator models is provided. A counting rate of a first gamma ray tool is simulated based on a model of a first blanket calibrator. When it is determined that the simulated counting rate matches a measured counting rate associated with the first gamma ray tool, a tally multiplier and a corresponding material specification for the model of the first blanket calibrator is determined. A counting rate for a second gamma ray tool is simulated based on the tally multiplier and the material specification determined for the model of the first blanket calibrator. A sensitivity factor for the second gamma ray tool is determined based on the simulation. The second gamma ray tool is calibrated according to a nominal blanket activity calculated from the sensitivity factor of the second gamma ray tool.

A method of determining a presence of stratigraphic traps includes obtaining a Gamma ray (GR) log dataset. The GR log dataset includes values for a plurality of wells in an area of interest. The method includes determining a geological time period corresponding to a depth in the GR log dataset; determining a spectrum of Earth’s orbital parameters corresponding to the geological time period; determining peak frequencies of the spectrum of Earth’s orbital parameters; and determining a quantity of orbital cycles per well in the area of interest. The spectrum of Earth’s orbital parameters includes parameters for eccentricity, obliquity, and precession. The orbital cycles may be reflected as sedimentary patterns in a geologic record. The method includes determining a presence of stratigraphic traps, based, at least in part, on differences in quantities of orbital cycles between one or more wells in the area of interest.

A method of creating a well image log of a cased well is provided. A passive cased well image logging tool assembly including a logging tool body, a plurality of gamma ray radiation sensors and a spatial positioning device is moved through at least a portion of the wellbore at a logging speed of no greater than 750 feet per hour. Corrected gamma ray radiation data is vertically sampled at a vertical distance sampling rate of once every vertical distance sampling interval, wherein the vertical distance sampling interval is no greater than 1.75 inches. Based on the sampled data, a well image log is prepared. A passive cased well image logging tool assembly for use in a cased well is also provided.

A method of creating a well image log of a cased well is provided. A passive cased well image logging tool assembly including a logging tool body, a plurality of gamma ray radiation sensors and a spatial positioning device is moved through at least a portion of the wellbore at a logging speed of no greater than 750 feet per hour. Corrected gamma ray radiation data is vertically sampled at a vertical distance sampling rate of once every vertical distance sampling interval, wherein the vertical distance sampling interval is no greater than 1.75 inches. Based on the sampled data, a well image log is prepared. A passive cased well image logging tool assembly for use in a cased well is also provided.

Systems and methods for developing a reservoir that include obtaining well log data (conducting nuclear magnetic resonance (NMR), gamma ray (GR), and resistivity logging operations to generate corresponding NMR, GR and formation true resistivity logs for one or more wells in the reservoir), determining rock property data based on the well log data, determining a “water-zone baseline” based on the rock property data (e.g., based on a cross-plot of rock properties determined from the NMR and GR logs and resistivity values), and determining water saturation data based on the water-zone baseline.

Systems and methods for developing a reservoir that include obtaining well log data (conducting nuclear magnetic resonance (NMR), gamma ray (GR), and resistivity logging operations to generate corresponding NMR, GR and formation true resistivity logs for one or more wells in the reservoir), determining rock property data based on the well log data, determining a “water-zone baseline” based on the rock property data (e.g., based on a cross-plot of rock properties determined from the NMR and GR logs and resistivity values), and determining water saturation data based on the water-zone baseline.