Multi-sector data correction method and system for gamma imaging while drilling
A multi-sector data correction method for gamma imaging while drilling includes the steps of: (a) dividing each gamma imaging sector into a plurality of counting zones; (b) counting a number of valid counting pulses for each counting zone at a predetermined time interval during MWD; (c) constructing a plurality of measurement vectors based on a value of recording times of each counting zone; (d) establishing a correction matrix with a conditional number less than a set value through an optimization algorithm; and (e) calculating a gamma intensity of each measured sector with the plurality of measurement vectors and the correction matrix as constructed, so as to complete the correction on the measurement data of each measured sector for each predetermined time interval. This method eliminate problems such as rotational measurement distortion of the gamma imaging while drilling tool and improve the accuracy of calculating the formation dip angle.
1 . A multi-sector data correction method for gamma imaging while drilling, comprising:
S 1 : placing a gamma imaging tool into a wellbore in a formation, wherein the gamma imaging tool comprises a gamma sensor with azimuth blanking and an acquisition circuit signally connected to the gamma sensor and a processor;
S 2 : dividing a circumference of the wellbore into a plurality of gamma imaging sectors, and dividing each gamma imaging sector into a plurality of counting zones, each counting zone corresponds to one tool face of the gamma imaging tool;
S 3 : counting a number of valid counting pulses for each counting zone at a predetermined time interval during measurement while drilling using the gamma sensor, which comprises:
S 31 : rotating the gamma imaging tool;
S 32 : transmitting a valid counting signal to the acquisition circuit upon receiving a valid counting pulse at the gamma sensor, and,
S 33 : recording, by the processor, a current tool face of the gamma imaging tool and a serial number of the counting zone corresponding to the current tool face;
S 4 : constructing a plurality of measurement vectors featuring measurement results of all the plurality of gamma imaging sectors based on a value of recording times of each counting zone;
S 5 : establishing a correction matrix with a conditional number less than a set value, said correction matrix being used to correct measurement data; and
S 6 : calculating a gamma intensity of each measured sector with the plurality of measurement vectors and the correction matrix as constructed to correct measurement data of each measured sector for each predetermined time interval.
2 . The multi-sector data correction method for gamma imaging while drilling according to claim 1 , wherein in S 4 , all the counting zones are divided into a plurality of groups, and the value of recording times of each counting zone in each group is used to construct a corresponding measurement vector,
wherein a number of groups into which the counting zones are divided is equal to a number of the counting zones formed by equally dividing each sector, and each group of counting zones is composed of the counting zones that are discontinuously extracted from each sector, any adjacent counting zones in a same sector not being in a same group.
3 . The multi-sector data correction method for gamma imaging while drilling according to claim 1 , wherein in S 6 , the gamma intensity G of each measured sector is calculated with an expression as follows:
G
=
γ
-
1
·
(
M
1
+
M
2
+
…
+
M
n
)
wherein M n denotes the n th measurement vector, γ is the correction matrix, γ=γ 1 +γ 2 + . . . +γ n , and γ n denotes the n th optimization matrix.
4 . The multi-sector data correction method for gamma imaging while drilling according to claim 3 , wherein in S 4 , all the counting zones are divided into two groups, and a first measurement vector and a second measurement vector are constructed respectively with the value of recording times per unit time for each counting zone in each group, wherein each group of the counting zones is formed by discontinuously extracting the counting zones from consecutive counting zones arranged along a circumferential direction, any adjacent counting zones not being in the same group;
wherein said first measurement vector is a one-dimensional vector, each vector unit of which is a value of recording times per unit time for each counting zone in a first group of counting zones, these values being arranged in a sequence corresponding to the counting zones in the circumferential direction; and
said second measurement vector is a one-dimensional vector, each vector unit of which is a value of recording times per unit time for each counting zone in a second group of counting zones, these values being arranged in a same way as those of the first measurement vector and with a same starting point.
5 . The multi-sector data correction method for gamma imaging while drilling according to claim 4 , wherein the step of constructing said correction matrix comprises:
determining a number of units within the correction matrix based on a number of groups of all counting zones;
setting an adjustment coefficient and multiple correction coefficients, wherein a number of correction coefficients is equal to a sum of a number of elements of the first measurement vector and that of the second measurement vector;
establishing, based on the adjustment coefficient and multiple correction coefficients, a correction unit matrix for each measurement vector, thereby forming the correction matrix; and
determining, based on the vector composed of said multiple correction coefficients as an independent variable, an optimal independent variable for which the conditional number of the correction matrix reaches or approaches a global minimum through an optimization algorithm, thereby obtaining an optimal correction matrix with the optimal independent variable.
6 . The multi-sector data correction method for gamma imaging while drilling according to claim 5 , wherein in S 5 , a correction matrix y with a conditional number less than 10 is constructed with an expression as follows:
γ
=
γ
1
+
γ
2
wherein γ 1 is expressed as follows:
γ
1
=
[
a
·
φ
1
φ
1
0
0
…
0
0
a
·
φ
3
φ
3
0
…
0
0
0
a
·
φ
5
φ
5
0
0
0
0
0
a
·
φ
7
φ
7
0
⋮
⋮
0
0
⋱
⋮
φ
2
n
-
1
0
0
0
…
a
·
φ
2
n
-
1
]
and γ 2 is expressed as follows:
γ
2
=
[
φ
2
a
·
φ
2
0
0
…
0
0
φ
4
a
·
φ
4
0
…
0
0
0
φ
6
a
·
φ
6
0
0
0
0
0
φ
8
a
·
φ
8
0
⋮
⋮
0
0
⋱
⋮
a
·
φ
2
n
0
0
0
…
φ
2
n
]
wherein n denotes a number of sectors to be measured, α denotes the adjustment coefficient, and [φ 1 , φ 2 , φ 3 , . . . , φ 2n ] denotes the vector of correction coefficients.
7 . The multi-sector data correction method for gamma imaging while drilling according to claim 6 , wherein in S 6 , the gamma intensity G of each measured sector is calculated with an expression as follows:
G
=
γ
-
1
·
(
M
1
+
M
2
)
wherein M 1 and M 2 denote the first and second measurement vectors, respectively, and γ denotes the correction matrix after optimization.
8 . A computer apparatus, comprising a processor and a memory, said memory being stored thereon at least one instruction, at least one program, a set of codes or a set of instructions, wherein said at least one instruction, at least one program, said set of codes or said set of instructions is loaded and executed by said processor to perform the multi-sector data correction method for gamma imaging while drilling according to claim 1 .
9 . A computer readable storage medium, stored thereon at least one instruction, at least one program, a set of codes or a set of instructions, wherein said at least one instruction, at least one program, said set of codes or said set of instructions is loaded and executed by said processor to perform the multi-sector data correction method for gamma imaging while drilling according to claim 1 .