A METHOD FOR DETERMINATION OF PROPERTIES OF CUTTINGS FROM ROCK DRILLING

Abstract

In a method for determination of properties of cuttings from rock drilling the cuttings are crushed between at least two rollers, at least one roller being driven by a motor. A mechanic specific energy of the cuttings is determined by measuring the energy applied by the motor.

Claims

1. A method for determination of properties of cuttings from rock drilling in which the cuttings are crushed between at least two rollers, at least one roller being driven by a motor, wherein a mechanic specific energy of the cuttings is determined by measuring the energy applied by the motor.

2. The method of claim 1, wherein the motor is an electric motor and that the electric energy applied by the electric motor is measured.

3. The method as claimed in claim 2, wherein the mechanic specific energy is calculated as $MSE=\frac{U*\eta }{V_r}*\left[{\int }_{t_s}^{t_e}I\left(t\right)\mathrm{dt}\right]$ where: MSE=mechanic specific energy, U=voltage, I=electric current, V.sub.r=volume of rock cuttings, η=mechanical efficiency of the crusher, t.sub.s=test start time, t.sub.e=test end time.

4. The method of claim 1, wherein the torque applied by the motor is measured.

5. The method as claimed in claim 4, wherein the energy applied by the motor is calculated as $MSE=\frac{\pi *\eta }{30*V_r}\left[{\int }_{\mathrm{ts}}^{\mathrm{te}}T\left(t\right)*n\left(t\right)*dt\right]$ where: MSE=mechanic specific energy, T=torque, n=rotational speed V.sub.r=volume of rock cuttings, η=mechanical efficiency of the crusher, t.sub.s=test start time, t.sub.e=test end time.

6. The method as claimed in claim 4, wherein the energy applied by the motor is calculated as $MSE=\frac{\pi *\eta }{30*V_r}\left[\underset{t_s}{\overset{t_e}{.Math.}}\left[T_i*n_i*\Delta t\right]\right]$ where: MSE=mechanic specific energy, T.sub.i=torque, n.sub.i=rotational speed Vr=volume of rock cuttings, η=mechanical efficiency of the crusher, Δt=time between to measurements t.sub.s=test start time, and t.sub.e=test end time.

7. The method as claimed in claim 1, wherein a fixed amount of rock cuttings is crushed.

8. The method as claimed in claim 1, wherein a fixed time is set to crush rock cuttings.

9. The method as claimed in claim 1, wherein a correlation between mechanic specific energy and unconfined compressive strength is developed and that based on this correlation unconfined compressive strength can be derived from mechanic specific energy data.

10. The method as claimed in claim 1, wherein a correlation between mechanic specific energy and cohesion is developed and that based on this correlation cohesion can be derived from mechanic specific energy data.

11. The method as claimed in claim 2, wherein a fixed amount of rock cuttings is crushed.

12. The method as claimed in claim 3, wherein a fixed amount of rock cuttings is crushed.

13. The method as claimed in claim 4, wherein a fixed amount of rock cuttings is crushed.

14. The method as claimed in claim 5, wherein a fixed amount of rock cuttings is crushed.

15. The method as claimed in claim 6, wherein a fixed amount of rock cuttings is crushed.

16. The method as claimed in claim 2, wherein a fixed time is set to crush rock cuttings.

17. The method as claimed in claim 3, wherein a fixed time is set to crush rock cuttings.

18. The method as claimed in claim 4, wherein a fixed time is set to crush rock cuttings.

19. The method as claimed in claim 5, wherein a fixed time is set to crush rock cuttings.

20. The method as claimed in claim 6, wherein a fixed time is set to crush rock cuttings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Other features and advantages of the invention will become more readily apparent from the following detailed description of exemplary and therefore not limitating examples taken in conjunction with the accompanying drawings, in which:

[0036] FIG. 1 is a device with which MSE data can be derived,

[0037] FIG. 2 is a plot showing the current versu time of a single test with the device of FIG. 1,

[0038] FIG. 3 is a plot showing the correlation between cohesion and MSE,

[0039] FIG. 4 is a plot showing the correlation between MSE and UCS, and

[0040] FIG. 5 is a plot showing the correlation of torque T and the number of revolutions n versus time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] A device 1 for determination of properties, in particular mechanic specific energy (MSE) of cuttings from rock drilling, has two rollers 2, 3, at least one roller 3 being driven by a motor 4. Cuttings 5 from rock drilling are fed into a gap 6 and crushed into smaller pieces. The width of the gap 6 can be adjusted according to particular characteristics (e.g. size, rock type, rigidity) of the cuttings.

[0042] The applied energy for crushing the cuttings is measured and represents—related to the passed cutting mass or volume—the MSE. The MSE necessary to crush the cuttings can be calculated in that the power of the motor 4 is integrated over a time interval necessary to crush a particular amount of rock cuttings. In an alternative embodiment a particular time interval can be set and cuttings are supplied to the gap 6 as long as the time interval lasts. Of course in this latter case it is necessary to measure the mass or volume of crushed cuttings after the process.

[0043] In case the motor 4 is an electric motor the current in the power line 7 is measured and recorded during the test and the mechanic specific energy MSE necessary to crush the rock cuttings 5 is calculated as follows:

[00003]$\mathrm{MSE}=\frac{U*\eta }{V_r}*\left[{\int }_{t_s}^{t_e}I\left(t\right)\mathrm{dt}\right]$

[0044] where:

[0045] U=voltage,

[0046] I=electric current,

[0047] V.sub.r=volume of rock cuttings,

[0048] η=mechanical efficiency of the crusher,

[0049] t.sub.s=test start time,

[0050] t.sub.e=test end time.

[0051] FIG. 2 is a plot of current versus time. The integral means the area below the curve 8 between test start time t.sub.s and test end time t.sub.e which is the measured current of the motor 4.

[0052] The MSE can be expressed in MPa, and it can be used as an indicator of the strength of the crushed rock.

[0053] The inventors found out that MSE measured and calculated as mentioned before shows a very good correlation to the unconfined compressive strength (UCS) and cohesion of rock cuttings. Therefore, based on this correlation UCS and cohesion can easily be derived from the MSE data.

[0054] In another embodiment of the application MSE is determined via the torque applided by the motor 4 to the driven roller 2. The torque can for example be determined by a torquemeter 9 attached to the output shaft 10 of the motor 4.

[0055] In this case the mechanic specific energy MSE can be calculated as

[00004]$MSE=\frac{\pi *\eta }{30*V_r}\left[{\int }_{t_s}^{t_e}T\left(t\right)*n\left(t\right)*dt\right]$

[0056] where:

[0057] MSE=mechanic specific energy,

[0058] T=torque,

[0059] n=rotational speed

[0060] Vr=volume of rock cuttings (6),

[0061] η=mechanical efficiency of the crusher,

[0062] t.sub.s=test start time, and

[0063] t.sub.e=test end time.

[0064] Instead of calculating MSE via an integral MSE can also be calculated as a sum of the product of individual records of the torque T.sub.i and the rotational speed n.sub.i and the time between two readings

[00005]$\left[{\int }_{t_s}^{t_e}T\left(t\right).Math.n\left(t\right).Math.\mathrm{dt}\right].fwdarw.\stackrel{t_e}{\underset{t_s}{.Math.}}\left[T_i*n_i*\Delta t\right]$

[0065] In this case the mechanic specific energy MSE can be calculated as

[00006]$MSE=\frac{\pi *\eta }{30*V_r}\left[\underset{t_s}{\overset{t_e}{.Math.}}\left[T_i*n_i*\Delta t\right]\right]$

[0066] where:

[0067] MSE=mechanic specific energy,

[0068] T.sub.i=torque,

[0069] n.sub.i=rotational speed

[0070] Vr=volume of rock cuttings (6),

[0071] η=mechanical efficiency of the crusher,

[0072] Δt=time between to measurements

[0073] t.sub.s=test start time, and

[0074] t.sub.e=test end time.

[0075] This embodiment of the invention is shown in FIG. 5. FIG. 5 shows a plot of torque T and the number of revolutions n versus time. The torque T.sub.i is captured at several times t.sub.i and the product of torque T.sub.i and number of revolutions n.sub.i is calculated each time. The more measureents are made in the time interval between test start time t.sub.s and test end time t.sub.e and the shorter Δt is the more precice is the calculation of the energy provided by motor 4.

[0076] FIG. 3 is a plot showing the correlation between cohesion and MSE. In a first step a correlation between MSE and cohesion had to be developed using standard testing methods in a laboratory for determination of cohesion of a particular rock type which on the other hand has been tested with the device 1 of FIG. 1.

[0077] FIG. 4 is a plot showing the correlation between UCS and MSE. As was the case with the relation between MSE and cohesion also in case of the correlation between UCS and MSE in a first step a correlation between MSE and UCS had to be developed using standard testing methods in a laboratory for determination of UCS of a particular rock type which on the other hand has been tested with the device 1 of FIG. 1.

[0078] Several tests were performed with the device 1 using different cement samples and rock samples. It is evident that the correlation of cohesion of cement samples is good as the cement does not have predominant grains; it is a homogeneous material with the same properties in the whole body. Unlike the cement, the sandstones tested are composed of grains of minerals and a cementing material between the grains that holds them together and may be composed of a matrix of silt or clay-size particles that fill the space between the grains. Although the UCS of both materials is the same (macro scale), there is a difference in the MSE required to crush a rock, since in a small scale (cuttings) the grain size and the cementing material acquire more importance in the crushing process.

[0079] After having determined the correlations between MSE, UCS and cohesion, respectively, these two correlations can be used to determine the properties of cement and rocks using cuttings from these materials after having tested these materials with the device 1 of FIG. 1 according to the method of the invention.