Neutron through-pipe measurement, device, system and use thereof
A method for evaluating a characteristic of a formation adjacent a wellbore comprises emitting a neutron field into the formation from a neutron source, obtaining data comprising a long neutron neutron (LNN), short neutron neutron (SNN), long neutron gamma (LNG) and short neutron gamma data (SNG) from the neutron field emitted into the formation and combining the long data with the short data to reduce error associated with the characteristic to be evaluated. A detector for evaluating a characteristic of a formation includes a neutron source and detectors for detecting LNN, SNN, LNG, SNG.
1. A method of evaluating a characteristic of a formation adjacent a wellbore comprising:
emitting a neutron field into the formation from a neutron source;
obtaining data comprising a long neutron neutron (LNN), short neutron neutron (SNN), long neutron gamma (LNG) and short neutron gamma data (SNG) from the neutron field emitted into the formation:
combining the long data with the short data to reduce error associated with the characteristic to be evaluated, wherein the characteristic is neutron porosity (QTP) and the formula for evaluating the characteristic QTP is:
QTP
=
A
*
ln
(
SNN
*
LNG
SNG
*
LNN
)
+
B
wherein A and B are determined empirically and are influenced by bit size and the amount of high dense material in a volume of investigation.
2. The method of claim 1 , further comprising the step of:
optimizing a spacing of a long neutron detector for detecting LNN and a short neutron detector for detecting SNN relative the neutron source to minimize the error associated to the characteristic to be evaluated.
3. The method of claim 1 , further comprising the step of:
optimizing a spacing of a long gamma detector for detecting LNG and a short gamma detector for detecting SNG relative the neutron source to minimize the error associated to the characteristic to be evaluated.
4. The method of claim 1 , wherein the data is obtained through a wellbore casing.
5. The method of claim 1 , wherein the combining step comprises the cancelation of the error associated to the long data with the error associated to the short data.
6. A method of evaluating a characteristic of a formation adjacent a wellbore comprising:
emitting a neutron field into the formation from a neutron source;
obtaining data comprising a long neutron neutron (LNN), short neutron neutron (SNN), lone neutron gamma (LNG) and short neutron gamma data (SNG) from the neutron field emitted into the formation;
combining the long data with the short data to reduce error associated with the characteristic to be evaluated, wherein the characteristic is neutron clay (QNC) and the formula for evaluating the characteristic QNC is:
QNC
=
A
*
(
C
(
SNG
LNG
)
+
D
*
(
SNN
LNN
)
)
+
B
wherein A, B, C and D are empirically determined coefficients.
7. The method of claim 6 , wherein A, B, C and D are 0.004, 0, 1.9 and −1.5, respectively.
8. The method of claim 1 , wherein the characteristic is neutron liquid (QNL) and the formula for evaluating the characteristic QNL is:
Q
N
L
=
A
*
ln
(
LNG
*
SNG
LNN
*
SNN
)
+
B
wherein A and B are chosen to create the best overlay of QNL to QTP.
9. The method of claim 1 , wherein the characteristic is water saturation (Sw) and the formula for evaluating the characteristic Sw is:
Sw
=
1
-
Kf
(
Q
E
P
-
Q
E
L
)
Q
E
P
wherein
k=fluid factor;
f=formation factor;
QEP=Quad Effective Porosity (Clay Free); and
QEL=Quad Effective Liquid porosity (Clay Free); and
wherein
QEP and QEL are determined as follows:
QEP=QTP−QC and QEL=QL−QC
wherein
QTP=Quad Total Porosity;
QC=Quad Clay Porosity; and
QL=Quad Liquid Porosity;
the fluid factor k= 1/(MaxPor*QLgain)
wherein
MaxPor=WaterPor−OilPor;
WaterPor is determined as follows:
WaterPor=(12.73+√{square root over (12.73 2 −4*0.0966*(403.04−Waterkppm)))}/(2*0.0966)
OilPor is determined as follows:
OilPor=0.1333*oilAPI+71 and
QLgain is computed as
QLgain=QNL A value/32.5.
10. The method of claim 6 , further comprising the step of:
optimizing a spacing of a long neutron detector for detecting LNN and a short neutron detector for detecting SNN relative the neutron source to minimize the error associated to the characteristic to be evaluated.
11. The method of claim 6 , further comprising the step of:
optimizing a spacing of a long gamma detector for detecting LNG and a short gamma detector for detecting SNG relative the neutron source to minimize the error associated to the characteristic to be evaluated.
12. The method of claim 6 , wherein the data is obtained through a wellbore casing.
13. The method of claim 6 , wherein the combining step comprises the cancelation of the error associated to the long data with the error associated to the short data.