Estimating Rock Properties Using Sound Levels from Drilling
Table 1: Test Conditions for the Determination of Sound Spectra in Granite
Noise Sources Background Air only
Air + drill with 100 N thrust Air + drill with 300 N thrust
Measured at Operator Position A1 A2 A3 A4
Table 2: Compressive Strength and Abrasivity of Different Rocks at an Air Pressure of 6.0 kg/cm2
Block No.
Block-1 Block-2 Block-3 Block-4 Block-5
Rock Type Shale
Hematite Limestone Granite Gabbros
Compressive
Strength (kg/cm2) 1,051.35 1,262.33 1,542.57 1,937.13 2,252.35
Abrasivity (%) 6
23.70 21.50 20.30 17.50 15.50
Figure 1: Effect on Leq Levels at the Operator’s Position for Test Conditions A1 and A21
105
85 95
75 65 55
Table 3: Leq Level Near Drill Bit for Different Rocks at Various Thrust and Air Pressures
Air Thrust
Pressure (N) (kg/cm2) 5
5.5 7
160 200 300 360 160 200 300 360 160 200 300 360 160 200 300 360
Shale
120.0 120.8 121.5 121.8 120.8 121.3 121.6 121.9 121.5 121.8 122.3 122.7 121.7 121.9 122.7 122.9
Hematite Limestone Granite Gabbros
121.0 121.5 122.0 122.1 121.2 121.7 122.3 122.6 121.7 121.9 122.6 122.8 122.0 122.4 123.1 123.5
121.2 121.7 122.1 122.3 121.6 122.2 122.7 122.9 122.0 122.3 122.9 123.2 122.2 122.7 123.6 123.8
121.6 122.0 122.3 122.5 121.8 122.5 122.9 123.3 122.4 122.7 123.2 123.7 122.5 122.9 123.9 124.0
121.9 122.3 122.5 122.7 122.2 122.7 122.9 123.7 122.7 122.9 123.6 123.9 122.9 123.1 124.8 124.9
5.0 kg/cm2 was 1.8 dB for shale, 1.1 dB for hematite and limestone, 0.9 dB for granite and 0.8 dB for gabbros. The effect of compressive strength of rock on the sound level near the drill bit for a constant thrust of 160 N for different air pressure values is shown in Figure 3.
0.03125/0.0625 0.125 0.25 0.5 1 Background noise, test condition A1 2 4 Nominal one-third-octave midland frequency (kHz)
(Exhaust noise + background noise), test condition A2
Figure 2: Effect on Leq Levels at the Operator’s Position for Test Conditions A2, A3 and A41
100 110
80 90
70 60 50
0.03125/0.0625 0.125 0.25 0.5 1 (Air only), test condition A2
(Air + drill with 100N thrust), test condition A3
2 4 Nominal one-third-octave midland frequency (kHz)
(Air + drill with 300N thrust), test condition A4
Both air pressure and thrust were observed to have a significant effect on the sound level. For example, an increase of 2.0 kg/cm2 in air pressure at a constant thrust of 160 N indicated an increase in sound level of 1.7 dB for block 1 and of 1.0 dB for blocks 2 to 5. The increase in sound level with an increase in thrust of 200 N at an air pressure of
26 8 16 8 16
Analytical Approach to Estimating Rock Properties Science is all about pursuing reasons to explain reality. Generally, these reasons are mathematical equations established between experimental conditions and observations. From simple classical physics to complex relativistic equations, all are formed with a view of satisfying the experimental observations under the scope of known dimensions. For instance, it has been observed that a piece of rock is compressed to a smaller volume when subjected to pressure from all sides. Looking for a reason for this by experimentation and analysis, one may end up finding a relationship between pressure applied and decrease in volume. Fortunately, it will yield a very sweet equation: ∆V = VP/B (where ∆V is decrease in volume, V is initial volume, B is bulk modulus of rock and P is uniform pressure applied). Now, if such relations are studied in depth (ignoring the uncertainties of quantum physics), the word ‘relationship’ can be changed to ‘function’ leading to the statement that ‘experimental observations are the function of experimental conditions’. This filtration is due to the fundamental definition of function containing one-to-one or many-to-one relations, but never one-to-many relations. In other words, it may be possible to obtain the same observations from several experimental conditions in a relation, but it is impossible to obtain several observation values from a single experimental condition. This can be mapped, as shown in Figure 4.
In the relation ∆V = VP/B (i.e. ∆V as a function of V, P and B), ∆V will be same for many values of V and P until the product VP is constant. There is no possibility under any known rules of mathematics by which to get two different values of ∆V for the same set of V, P and B values. Cases such as Y = ±X, where one can get two values of Y for the same X, cannot be used as functions.
The development of an analytical approach to estimating rock properties is difficult to understand regarding the relationship between noise level during drilling, rock properties and various drilling conditions. To analyse the relation, rock properties and various drilling parameters can be categorised into the domain of experimental
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2
A-weighted sound pressure level (dB)
A-weighted sound pressure level (dB)
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