Prediction method for coal and gas outburst based on comparing borehole gas flow curves
A prediction method for coal and gas outburst based on comparing borehole gas flow curves includes the following steps: constructing a seam-crossing borehole in the coal seam, measuring or calculating gas flow corresponding to critical gas pressure P, which is a reference gas flow Q(t) reference ; performing linear regression on the reference gas flow Q(t) reference to form a reference flow curve; constructing a predicted seam-crossing borehole in a predicted area, and directly testing a gas flow at each time t in a delayed manner, which is a predicted gas flow Q(t) prediction ; performing linear regression on the predicted gas flow Q(t) prediction to form a predicted flow curve; and judging whether the predicted flow curve is above the reference flow curve or whether the predicted flow curve intersects with the reference flow curve, and judging whether the coal seam in the predicted area has a risk of coal and gas outburst.
1. A prediction method for coal and gas outburst based on comparing borehole gas flow curves, under a same coal seam condition in a same coal mine, the prediction method comprising following steps:
(A) constructing a No. 1 seam-crossing borehole and determining a gas pressure P determination 1 of a coal seam;
(B) judging the determined gas pressure P determination 1 of the coal seam, if the determined gas pressure P determination 1 of the coal seam is greater than or equal to 0.70 megapascal (MPa) and smaller than or equal to 0.74 MPa, testing a first gas flow at each time t in a delayed manner to be used as a reference gas flow Q(t) reference , and directly executing step (H);
(C) if P determination 1 is smaller than 0.70 MPa or P determination 1 is greater than 0.74 MPa, testing a gas flow Q(t) test 1 at each time t in the delayed manner, and executing step (D) to step (F);
(D) constructing a No. 2 seam-crossing borehole and determining a gas pressure P determination 2 of the coal seam;
(E) judging the determined gas pressure P determination 2 of the coal seam, if the determined gas pressure P determination 2 of the coal seam is greater than or equal to 0.70 MPa and smaller than or equal to 0.74 MPa, testing a second gas flow at each time t in the delayed manner to be used as the reference gas flow Q(t) reference , and directly executing step (H);
(F) if P determination 2 is smaller than 0.70 MPa or P determination 2 is greater than 0.74 MPa, testing a gas flow Q(t) test 2 at each time t in the delayed manner, and executing step (G);
(G) calculating a third gas flow corresponding to a critical gas pressure P to be used as the reference gas flow Q(t) reference , wherein a following formula is used for calculation:
D
(
t
)
=
Q
(
t
)
test
1
-
Q
(
t
)
test
2
P
determination
1
-
P
determination
2
,
wherein D(t) is a gas pressure coefficient which indicates a difference value of gas flow at each time t under a condition that there is a difference of 1 MPa between gas pressure, and t is 0.08 hour, 0.5 hour, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 10 hours, 24 hours, 48 hours, 72 hours, 96 hours, 120 hours;
if |P−P determination 1 |<|P−P determination 2 |, wherein P is the critical gas pressure, P=0.74 MPa, a following formula is used for calculation:
Q ( t ) reference =Q ( t ) test 1 +(0.74− P determination 1 )· D ( t ),
and the gas flow at each time t, corresponding to the critical gas pressure P=0.74 MPa, is calculated and used as the reference gas flow Q(t) reference ;
if |P−P determination 1 |≥|P−P determination 2 |, wherein P is the critical gas pressure, P=0.74 MPa, a following formula is used for calculation:
Q ( t ) reference =Q ( t ) test 2 +(0.74− P determination 2 )· D ( t ),
and the gas flow at each time t, corresponding to the critical gas pressure P=0.74 MPa, is calculated and used as the reference gas flow Q(t) reference ;
(H) performing a linear regression on the reference gas flow Q(t) reference obtained in the step (B) or the step (E) or the step (G), and using a formed borehole gas flow curve as a reference flow curve;
(I) constructing a predicted seam-crossing borehole in a predicted area, and directly testing the gas flow at each time t in the delayed manner to be used as a predicted gas flow Q(t) prediction ;
(J) performing the linear regression on the predicted gas flow Q(t) prediction , and using a formed gas flow curve as a predicted flow curve; and
(K) judging whether the predicted flow curve is above the reference flow curve or whether the predicted flow curve intersects with the reference flow curve, if yes, predicting that the coal seam in the predicted area has a risk of coal and gas outburst, or else, predicting that the coal seam in the predicted area does not have the risk of coal and gas outburst.
2. The prediction method of claim 1 , wherein testing the gas flow at each time t in the delayed manner means respectively testing the gas flow when each time t is 0.08 hour, 0.5 hour, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 10 hours, 24 hours, 48 hours, 72 hours, 96 hours and 120 hours in the delayed manner.
3. The prediction method of claim 1 , wherein performing the linear regression on the reference gas flow Q(t) reference means selecting a curve with a highest fitting degree from exponential function curves, or power function curves or polynomial function curves.
4. The prediction method of claim 1 , wherein performing the linear regression on the predicted gas flow Q(t) prediction means selecting a curve with a highest fitting degree from exponential function curves, or power function curves or polynomial function curves.