Prediction method for coal and gas outburst based on comparing borehole gas flow curves

Abstract

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).sub.reference; performing linear regression on the reference gas flow Q(t).sub.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).sub.prediction; performing linear regression on the predicted gas flow Q(t).sub.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.

Claims

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.sub.determination 1 of a coal seam; (B) judging the determined gas pressure P.sub.determination 1 of the coal seam, if the determined gas pressure P.sub.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).sub.reference, and directly executing step (H); (C) if P.sub.determination 1 is smaller than 0.70 MPa or P.sub.determination 1 is greater than 0.74 MPa, testing a gas flow Q(t).sub.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.sub.determination 2 of the coal seam; (E) judging the determined gas pressure P.sub.determination 2 of the coal seam, if the determined gas pressure P.sub.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).sub.reference, and directly executing step (H); (F) if P.sub.determination 2 is smaller than 0.70 MPa or P.sub.determination 2 is greater than 0.74 MPa, testing a gas flow Q(t).sub.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).sub.reference, wherein a following formula is used for calculation: $D\left(t\right)=\frac{{Q\left(t\right)}_{\mathrm{test}\text{1}}-{Q\left(t\right)}_{\mathrm{test}\text{2}}}{{P_{\mathrm{determination}\text{1}}}_{}-P_{\mathrm{determination}\text{2}}},$ 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.sub.determination 1|<|P−P.sub.determination 2|, wherein P is the critical gas pressure, P=0.74 MPa, a following formula is used for calculation:
Q(t).sub.reference=Q(t).sub.test 1+(0.74−P.sub.determination 1).Math.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).sub.reference; if |P−P.sub.determination 1|≥|P−P.sub.determination 2|, wherein P is the critical gas pressure, P=0.74 MPa, a following formula is used for calculation:
Q(t).sub.reference=Q(t).sub.test 2+(0.74−P.sub.determination 2).Math.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).sub.reference; (H) performing a linear regression on the reference gas flow Q(t).sub.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).sub.prediction; (J) performing the linear regression on the predicted gas flow Q(t).sub.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).sub.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).sub.prediction means selecting a curve with a highest fitting degree from exponential function curves, or power function curves or polynomial function curves.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a flowchart of step (A) to step (G) of a prediction method for coal and gas outburst based on comparing borehole gas flow curves according to the present invention;

(2) FIG. 1B is a flowchart of step (H) to step (K) of a prediction method for coal and gas outburst based on comparing borehole gas flow curves according to the present invention;

(3) FIG. 2 is a schematic diagram of comparison of a reference flow curve and a predicted flow curve, obtained through measuring points in embodiment 1; and

(4) FIG. 3 is a schematic diagram of comparison of the reference flow curve and the predicted flow curve, obtained through calculation in embodiment 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) The technical solutions in embodiments of the present invention will be clearly and fully described below in connection with the accompanying drawings in embodiments of the present invention, and it will be apparent that the described embodiments are only some but not all embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by a person of ordinary skill in the art without making inventive effort are within the scope of protection of the present invention.

Embodiment 1

(6) With reference to FIG. 1A, FIG. 1B and FIG. 2, a prediction method for coal and gas outburst based on comparing borehole gas flow curves includes following steps under a same coal seam condition in a same coal mine:

(7) (A) Constructing a No. 1 seam-crossing borehole and determining a gas pressure P.sub.determination 1 of a coal seam to be equal to 0.73 MPa.

(8) (B) Judging the determined gas pressure P.sub.determination 1 of the coal seam, if the determined gas pressure P.sub.determination 1 of the coal seam is greater than or equal to 0.70 MPa and smaller than or equal to 0.74 MPa, testing a first 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 a delayed manner to be used as reference gas flow Q(t).sub.reference.

(9) (H) Performing a power function linear regression on the reference gas flow Q(t).sub.reference, so as to obtain Q(t).sub.reference=5.4294t.sup.−0.228 as a reference flow curve, wherein a fitting degree is R.sup.2=0.9136.

(10) (I) Constructing a predicted seam-crossing borehole in a predicted area (the predicted area is located in the same coal seam of the same coal mine as the No. 1 seam-crossing borehole constructed in the step (A), and has the same or similar parameters as the No. 1 borehole constructed in the step (A), and the borehole parameters mainly include borehole inclination, rock hole length and coal seam hole length), and testing the predicted gas flow Q(t).sub.prediction 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.

(11) (J) Performing the power function linear regression on the predicted gas flow Q(t).sub.prediction, so as to obtain a gas flow curve as a predicted flow curve Q(t).sub.prediction=3.5198t.sup.−0.261, wherein a fitting degree is R.sup.2=0.7018.

(12) (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.

(13) As shown in FIG. 2, the predicted flow curve Q(t).sub.prediction in the embodiment 1 is below the reference flow curve Q(t).sub.reference, so that the predicted area does not have coal and gas outburst risk.

Embodiment 2

(14) With reference to FIG. 1A, FIG. 1B and FIG. 3, a prediction method for coal and gas outburst based on comparing borehole gas flow curves includes following steps under a same coal seam condition in a same coal mine:

(15) (A) Constructing a No. 1 seam-crossing borehole and determining a gas pressure P.sub.determination 1 of a coal seam to be equal to 0.53 MPa.

(16) (B) If the formula that P.sub.determination 1 is greater than or equal to 0.70 MPa and smaller than or equal to 0.74 MPa fails, executing the following step (C).

(17) (C) If P.sub.determination 1 is smaller than 0.70 MPa, testing a gas flow Q(t).sub.test 1 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.

(18) (D) Constructing a No. 2 seam-crossing borehole and determining a gas pressure P.sub.determination 2 of the coal seam to be equal to 0.91 MPa.

(19) (E) If the formula that P.sub.determination 2 is greater than or equal to 0.70 MPa and smaller than or equal to 0.74 MPa fails, executing the following step (F).

(20) (F) If P.sub.determination 2 is greater than 0.74 MPa, testing a gas flow Q(t).sub.test 2 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.

(21) (G) Calculating a third gas flow corresponding to a critical gas pressure P to be used as the reference gas flow Q(t).sub.reference, wherein a following formula is used for calculation:

(22) $D\left(t\right)=\frac{{Q\left(t\right)}_{\mathrm{test}\text{1}}-{Q\left(t\right)}_{\mathrm{test}\text{2}}}{{P_{\mathrm{determination}\text{1}}}_{}-P_{\mathrm{determination}\text{2}}},$
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;
and besides, |P−P.sub.determination 1|=|0.74-0.53|=0.21>|P−P.sub.determination 2|=|0.74-0.91|=0.17, wherein P is the critical gas pressure, P=0.74 MPa, a following formula is used for calculation:
Q(t).sub.reference=Q(t).sub.test 2+(0.74−P.sub.determination 2).Math.D(t),
namely calculating the gas flow corresponding to the critical gas pressure P=0.74 MPa as the reference gas flow Q(t).sub.reference.

(23) (H) Performing a power function linear regression on the reference gas flow Q(t).sub.reference, so as to obtain Q(t).sub.reference=4.9625t.sup.−0.232 as a reference flow curve, wherein a fitting degree is R.sup.2=0.9293.

(24) (I) Constructing a predicted seam-crossing borehole in a predicted area (the predicted area is located in the same coal seam of the same coal mine as the constructed No. 1 seam-crossing borehole and the constructed No. 2 seam-crossing borehole, and has the same or similar parameters as the No. 1 borehole constructed in the step (A) and No. 2 borehole constructed in the step (D), and the borehole parameters mainly include borehole inclination, rock hole length and coal seam hole length), and testing the predicted gas flow Q(t).sub.prediction 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.

(25) (J) Performing the power function linear regression on the predicted gas flow Q(t).sub.prediction, so as to obtain a gas flow curve as a predicted flow curve Q(t).sub.prediction=3.9494t.sup.−0.319, wherein a fitting degree is R.sup.2=0.6674.

(26) (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.

(27) As shown in FIG. 3, the predicted flow curve Q(t).sub.prediction in the embodiment 2 is below the reference flow curve Q(t).sub.reference, so that the predicted area does not have coal and gas outburst risk.

(28) In this paper, several embodiments are used for illustration of the principles and implementations of the present invention. The description of the foregoing embodiments is used to help illustrate the method of the present invention and the core principles thereof. In addition, those of ordinary skilled in the art can make various modifications in terms of specific implementations and scope of application in accordance with the teachings of the present invention. In conclusion, the content of the description shall not be construed as a limitation to the present invention.