Method for Determining Geology While Drilling

Abstract

A method for determining the geology at a geographical location while drilling is disclosed, which method includes the steps of: performing sonic drilling with a drill pipe, a sonic drilling head, wherein the drill pipe is coupled to the sonic drilling head and wherein the sonic drilling head has vibration means for vibrating the drill pipe; measuring the vibrations of the drill pipe during drilling; converting the measured vibrations from the time domain to the frequency domain by applying a Fourier transformation; and determining the soil composition at the momentary drill depth by comparing the frequency pattern from the Fourier transformation with predefined frequency patterns for different soil compositions.

Claims

1. A method for determining the geology at a geographical location while drilling, which method comprises the steps of: performing sonic drilling with a drill pipe, a sonic drilling head, wherein the drill pipe is coupled to the sonic drilling head and wherein the sonic drilling head has vibration means for vibrating the drill pipe; measuring the vibrations of the drill pipe during drilling; converting the measured vibrations from the time domain to the frequency domain by applying a Fourier transformation; and determining the soil composition at the momentary drill depth by comparing the frequency pattern from the Fourier transformation with predefined frequency patterns for different soil compositions.

2. The method according to claim 1, further comprising the step of: adjusting the drilling parameters, such as drill force, drill speed, and the frequency of the vibrations with which the drill pipe is vibrated, based on the determined soil composition for the momentary drill depth.

3. The method according to claim 1, further comprising the step of: combining the determined soil compositions at the plurality of momentary drill depths to compose the geology at the geographical location.

4. The method according to claim 1, wherein for comparing of the frequency pattern from the Fourier transformation with predefined frequency patterns for different soil compositions a probabilistic, or fuzzy, matching algorithm is used.

5. The method according to claim 1, wherein the predefined frequency patterns are defined by repeating a plurality of times the following steps at different geographic locations: performing sonic sample drilling with a hollow drill pipe, a sonic drilling head, wherein the drill pipe is coupled to the sonic drilling head and wherein the sonic drilling head has vibration means for vibrating the drill pipe; measuring the vibrations of the drill pipe during drilling; converting the measured vibrations from the time domain to the frequency domain by applying a Fourier transformation; storing the frequency pattern from the Fourier transformation for the specific drilling depth; after reaching an end depth, retracting the hollow-drill pipe; examining the sample contained in the hollow drill pipe for the soil composition along the length of the sample; matching the soil composition at a position along the length of the sample with the stored frequency pattern for a specific drilling depth to compose a predefined frequency pattern for the soil composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] These and other features of the invention will be elucidated in conjunctions with the accompanying drawings.

[0039] FIG. 1 shows schematically the steps of the sonic drilling into the ground and the registration of the vibrations of the drilling pipe of an embodiment of the invention.

[0040] FIG. 2 shows the further step of conversion of the vibrations from the time domain into the frequency domain.

[0041] FIG. 3 shows the step of comparing the converted frequency pattern with predefined frequency patterns.

[0042] FIG. 1 shows a cross-section of the geology at a specific geographic location. A sonic drill rig 1 is positioned on the surface 2. The sonic drill rig 1 has sonic drilling head 3 and a drill pipe 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0043] When drilling a hole into the ground, the drill pipe 4 has passed a number of distinctive ground layers A, B, C. Typically sonic drilling is performed with a constant speed of the drill pipe 4 into the ground and as a result the depth and time are linked in this example. The measured vibrations of the drill pipe 4 are shown in the diagram 5. The time t and the depth d linked therewith are shown on the X-axis, while the frequency f of the vibrations is shown on the Y-axis.

[0044] In the diagram 5 the vibrations for the distinctive ground layers A, B, C are clearly visible.

[0045] FIG. 2 shows schematically the step of converting the measured vibrations for each distinctive ground layers A, B, C from the time domain 5A, 5B, 5C to the frequency domain 6A, 6B, 6C by applying a Fourier transformation. Each frequency domain diagram 6A, 6B, 6C shows on the X-axis the frequency f and on the Y-axis the amplitude A.

[0046] The frequency domain diagram 6A, 6B, 6C show a clear pattern of characteristic frequencies and amplitudes, which characterize the soil composition for a specific layer in the geology.

[0047] These frequency patterns 6A, 6B, 6C are then compared with predefined frequency patterns 7A, 7B, 7C, 7D (see FIG. 3) There is a clear match between the measured and converted frequency pattern 6A and the predefined frequency pattern 7C. The predefined frequency pattern 7C is for example characteristic for a lime soil composition. This allows the drill rig operator to adjust any drilling parameters based on determined geology at which the drill pipe is currently drilling.

[0048] The predefined frequency patterns 7A-7D are obtained with the similar method as described above. Instead of comparing the converted measured frequencies to a predefined pattern, the real sample of the soil composition is examined to link the converted measured frequency pattern with the actual soil composition, such that such a pattern can be used as a predefined frequency pattern.

[0049] By repeating this for a number of geographic locations, where the geology differs, the amount of data for the predefined frequency patterns is increased, which improves the accuracy for the matching of measured frequencies during drilling with the predefined frequency patterns.