Method and apparatus for measuring neutron characteristics of material surrounding a borehole

Claim 3

The method for logging of claim 1 wherein said third and said fourth time intervals are contiguous and of equal duration.

Claim 4

The method for logging of claim 2 wherein said third time interval is automatically controlled to start from between 200-400 microseconds following said subsequent neutron burst and said fourth time interval is controlled to start from between 400-600 microseconds following said subsequent neutron burst.

Claim 5

The method for logging of claim 3 wherein said first and said second time intervals are contiguous and of equal duration.

Claim 6

The method for logging of claim 4 wherein said first time interval is from between 400-600 microseconds after said burst of high energy neutrons and said second time interval is from between 600-800 microseconds following said burst of high energy neutrons.

Claim 7

The method for logging of claim 5 wherein said bursts of high energy neutrons are 1000 microseconds apart.

Claim 8

The method for logging of claim 6 further comprising deriving a ratio of said measured radiations during said first and said second intervals, said ratio being substantially representative of the decline of the neutron population in said formations.

Claim 9

The method for logging of claim 7 further comprising deriving a ratio of said measured radiations during said third and said fourth intervals, said ratio being substantially representative of the decline of the neutron population in said formations.

Claim 10

The method for logging of claim 8 wherein said ratio of said third and said fourth intervals is recorded in relation to borehole depth.

Claim 13

The method of claim 10 wherein said third time interval is controlled to begin from between 200-400 microseconds following said neutron burst.

Claim 14

The method of claim 11 wherein said third and said fourth time intervals are contiguous and of equal duration.

Claim 15

The method of claim 12 wherein said third and said fourth time intervals are of 200 microseconds in duration.

Claim 16

The method of claim 13 wherein said first and said second time intervals are contiguous and of equal duration.

Claim 17

The method of claim 14 wherein said bursts of high energy neutrons are approximately 1000 microseconds apart and said first time interval is from between 400-600 microseconds after said burst and said second time interval is from between 600-800 microseconds following said burst.

Claim 18

The method of claim 15 wherein said first electrical signal represents the ratio of said radiation within said first and said second intervals and said second signal represents the ratio of said radiation within said third and said fourth intervals.

Claim 19

Apparatus for logging the formations surrounding an earth borehole, comprising: an elongated instrument adopted to traverse on earth borehole; a pulsed source of high energy neutrons in said instrument for emitting bursts of high energy neutrons; a radiation detector in said instrument for detecting radiation emanating from said irradiated formations; means for measuring said detected radiations during first and second fixed time duration intervals following a burst of neutrons from said source; means for measuring said detected radiations during third and fourth fixed time duration intervals following a subsequent burst from said source; and means for automatically controlling the starting time of said third measurement interval in accordance with said measurement from said first and second intervals.

Claim 20

Apparatus for logging the formations surrounding an earth borehole, comprising: an elongated instrument adopted to traverse on earth borehole; a pulsed source of high energy neutrons in said instrument for emitting bursts of high energy neutrons; a radiation detector in said instrument for detecting radiation emanating from said irradiated formations; means for measuring said detected radiations during first and second fixed time duration intervals following a burst of neutrons from said source; means for measuring said detected radiations during third and fourth fixed time duration intervals following a subsequent burst from said source; and means for automatically controlling the starting time of said third measurement interval in accordance with said measurement from said first and second intervals.

Claim 21

The apparatus according to claim 17 further comprising means for starting said fourth time interval contiguous with said third time interval.

Claim 22

The apparatus of claim 18 wherein said third and said fourth time intervals are of equal time duration.

Claim 23

The apparatus of claim 19 wherein said third time interval is controlled to start from between 200-400 microseconds following said neutron burst.

Claim 24

The apparatus of claim 20 wherein said third and said fourth time intervals are 200 microseconds in duration.

Claim 25

The apparatus of claim 21 wherein said first and said second time intervals are contiguous and of equal duration.

Claim 26

The apparatus of claim 22 wherein said first and second time intervals are 200 microseconds in duration.

Claim 27

The apparatus of claim 23 wherein said bursts of high energy neutrons are 1000 microseconds apart.

Claim 28

Apparatus for logging the formations surrounding an earth borehole, comprising: a source for pulsedly irradiating said formations with discrete bursts from a source of high energy neutrons; a detector for detecting radiations emanating from said irradiated formations; means for generating electrical signals indicative of said detected radiations; means for gating said electrical signals indicative of said detected radiation for a first time interval following each of said bursts of high energy neutrons; means for gating said electrical signals indicative of said detected radiation for a second time interval following each of said bursts of high energy neutrons; means for gating said electrical signals indicative of said detected radiation for a third time interval following each of said bursts of high energy neutrons; means for gating said electrical signals indicative of said detected radiation for a fourth time interval following each of said bursts of high energy neutrons; means for automatically controlling the starting time of said third and said fourth time intervals in response to said electrical signals from said first and said second time intervals derived from a preceeding irradiation interval.

Claim 29

Apparatus for logging the formations surrounding an earth borehole, comprising: a source for pulsedly irradiating said formations with discrete bursts from a source of high energy neutrons; a detector for detecting radiations emanating from said irradiated formations; means for generating electrical signals indicative of said detected radiations; means for gating said electrical signals indicative of said detected radiation for a first time interval following each of said bursts of high energy neutrons; means for gating said electrical signals indicative of said detected radiation for a second time interval following each of said bursts of high energy neutrons; means for gating said electrical signals indicative of said detected radiation for a third time interval following each of said bursts of high energy neutrons; means for gating said electrical signals indicative of said detected radiation for a fourth time interval following each of said bursts of high energy neutrons; means for automatically controlling the starting time of said third and said fourth time intervals in response to said electrical signals from said first and said second time intervals derived from a preceeding irradiation interval.

Claim 30

The apparatus of claim 25 further comprising means for deriving a ratio of said electrical signals from said first time interval and said electrical signals from said second time interval, said ratio being substantially representative of the decline of the neutron population in said formation.

Claim 31

The apparatus of claim 26 further comprising means for deriving a ratio of said electrical signals from said third time interval and said electrical signals from said fourth time interval, said ratio being substantially representative of the decline of the neutron population in said formation.

Claim 32

The apparatus of claim 27 further comprising means for recording said ratio derived from said third and said fourth electrical signals.