Method and apparatus utilizing microwave electromagnetic energy for investigating earth formations

Apparatus for investigating earth formations surrounding a borehole which contains drilling mud and has a mudcake formed on a substantial portion of its walls, to obtain an indication of the dielectric constant of the formations, comprising:

• a. a member adapted for engagement with the borehole wall;
• b. means positionable in the borehole for injecting microwave electromagnetic energy into the surrounding formations and for establishing a lateral wave of such energy within the surrounding formations, said lateral wave traveling adjacent the interface between the mudcake and the formations;
• c. first and second receiving antennas mounted in spaced relation on the wall-engaging face of said member for receiving said microwave electromagnetic energy;
• and
• d. means coupled to said antennas for measuring the velocity of propagation of said lateral wave received at said first and second antennas, said velocity being indicative of the dielectric constant of formations surrounding the first and second antennas.

Apparatus for investigating earth formations surrounding a borehole to obtain an indication of the dielectric constant of the formations, comprising:

• a. a member adapted for engagement with the borehole wall;
• b. means mounted in said member for injecting microwave electromagnetic energy into the surrounding formations;
• c. first and second receiving antennas mounted in spaced relation on the wall-engaging face of said member for receiving said microwave electromagnetic energy;
• and
• d. means coupled to said antennas for measuring the phase difference between signals received at said first and second antennas, said phase difference being indicative of the dielectric constant of the formations surrounding said first and second antennas.

A method of determining the dielectric constant of formations surrounding a borehole, comprising the steps of:

• a. injecting microwave electromagnetic energy into the formations surrounding the borehole to establish a lateral wave in the surrounding formations;
• b. receiving wave energy from said lateral wave at first and second receiving locations within the borehole;
• and
• c. measuring the phase difference between wave energy received at said first and second receiving locations, said phase difference being indicative of the dielectric constant of the formations surrounding the area between the first and second receiving locations.

A method of determining the dielectric constant of earth formations surrounding a borehole, comprising the steps of:

• a. providing a member engageable with the borehole wall;
• b. injecting microwave electromagnetic energy into the surrounding formations from a transmitting antenna in said member;
• c. providing first and second receiving antennas in said member for receiving said microwave electromagnetic energy;
• and
• d. measuring the phase difference between signals received at said first and second receiving antennas, the phase difference being indicative of the dielectric constant of the formations surrounding the first and second receiving antennas.

A method of determining the dielectric constant of formations surrounding a borehole, comprising the steps of:

• a. deriving a quantity representative of the phase constant of microwave energy passing through the formations at a particular depth range of the borehole;
• b. deriving a quantity representative of the attenuation constant of microwave energy passing through the formations at the particular depth range of the borehole;
• and
• c. computing the dielectric constant at the particular depth range by combining the derived quantity representative of the phase constant with the derived quantity representative of the attenuation constant.

A method of determining the dielectric constant of formations surrounding a borehole, comprising the steps of:

• a. deriving a quantity .beta..sup.2, where .beta. is the phase constant associated with microwave energy passing through the formations at a particular depth of the borehole;
• b. deriving a quantity .alpha..sup.2, where .alpha. is the attenuation constant associated with microwave energy passing through the formations at the particular depth of the borehole;
• and
• c. computing the quantity .beta..sup.2 -.alpha..sup.2 which is proportional to the loss-corrected dielectric constant of the formations at the particular depth range.