Method and apparatus for measuring mud and formation properties downhole

A method for determining density of a mud mixture within a borehole in which a drilling tool is received, comprising:

• defining a bottom angular sector of said borehole;
• defining at least one more angular sector of said borehole;
• applying gamma rays into said mud mixture from a radiation source;
• recording, with respect to an angular position of said tool with respect to the borehole a count rate of gamma rays which return to a sensor disposed on the tool near the radiation source such that the count rate results from interaction between the gamma rays predominantly with said mud mixture or interaction between the gamma rays with the mud mixture and a formation area just beyond the borehole;
• determining at least a density of the mud mixture from the count rate of gamma rays for the at least one more of the sectors.

A method for determining a photoelectric effect (PEP) of a mud mixture within a borehole in which a tool is received, said tool including a source of radiation and a gamma ray detector, the method comprising:

• turning said tool in said borehole;
• applying energy into said borehole from an energy source disposed in said tool;
• recording measurement signals received at a sensor disposed in said tool from locations azimuthally distributed around said borehole, the sensor being located near the energy source such that a received measurement signal relates to interaction between applied energy with predominantly the mud mixture or interaction between the applied energy with the mud mixture and a formation area just beyond the borehole;
• separating a cross-section of the borehole substantially perpendicular to a longitudinal axis of the borehole into at least a first sector and a second sector, wherein a first measurement signal from said first sector is substantially in response to returning energy which results from the interaction of the applied energy with said mud mixture;
• and
• a second measurement signal from said second sector is substantially in response to returning energy which results from the interaction of the applied energy with said formation;
• determining a density (ρ), of the mud mixture, calculated from said first measurement signal;
• determining a macroscopic cross section (U), of the mud mixture from said first measurement signal, and
• determining the PEF of said mud mixture as a ratio of said macroscopic cross section to said density, that is, PEF=U/ρ.

A method for determining hydrogen index of a mud mixture surrounding a drilling tool within a borehole in which said drilling tool is received, comprising;

• defining a bottom angular sector of said borehole;
• defining at least one more angular sector of said borehole;
• applying neutrons into said mud mixture from a radiation source;
• recording, with respect to an angular position of said tool with respect to the borehole a count rate of neutrons which return to a sensor disposed on the tool near the radiation source such that the count rate results from interaction between the neutrons predominantly with said mud mixture or interaction between the neutrons with the mud mixture and a formation area just beyond the borehole;
• and
• determining at least a hydrogen index of the mud mixture from the count rate of neutrons for the at least one more of the angular sectors of said borehole.

A method for determining salinity of a mud mixture within a borehole in which a drilling tool is received, comprising:

• defining a bottom angular sector of said borehole;
• defining at least one more angular sector of said borehole;
• applying neutrons into said mud mixture from a radiation source;
• recording, with respect to an angular position of said tool with respect to the borehole a count rate of neutrons which return to a sensor disposed on the tool near the radiation source such that the count rate results from interaction between the neutrons predominantly with said mud mixture or interaction between the neutrons with the mud mixture and a formation area beyond the borehole;
• determining at least a salinity of the mud mixture from the count rate of neutrons for the at least one or more of the sectors of said borehole.

A method for determining a characteristic of a mud mixture surrounding a drilling tool within a borehole in which a drilling tool is received, comprising:

• defining a cross-section of said borehole which is orthogonal to a longitudinal axis of said tool;
• applying energy into said borehole from an energy source disposed in said tool;
• recording measurement signals received at a plurality of azimuthally distributed sensors disposed in said tool from a plurality of locations around said borehole, the sensors being located near the energy source such that a received measurement signal relates to interaction between the applied energy with predominantly the mud mixture or interaction between the applied energy with the mud mixture and a formation area just beyond the borehole;
• separating said cross-section into at least a first sector and a second sector, wherein a first measurement signal from ones of said sensors disposed in said first sector is substantially in response to returning energy which results from the interaction of the applied energy with said mud mixture;
• and a second measurement signal from ones of said sensors disposed in said second sector is substantially in response to returning energy which results from the interaction of the applied energy with said formation;
• and
• deriving an indication of an intrinsic characteristic of said mud mixture from said first measurement signals associated with the first sector of said borehole.