Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Land-reflection type
Patent
1986-01-22
1988-01-05
Tarcza, Thomas H.
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Land-reflection type
367 41, 181106, G01V 100, G01V 140
Patent
active
047180480
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of instantaneous acoustic logging within a wellbore and more generally to a method for continuously measuring the acoustic characteristics of subsurface strata which surround the wellbore.
During well-drilling operations, a certain number of physical measurements known as well logs are made in subsurface strata which are also known as formations and through which a drilling tool passes.
A certain number of well logs are produced while the drilling operation proper is in progress and these are known as instantaneous logs whereas other logs are produced during periods of interruption of drilling operations and these are known as delayed logs.
The well logs thus obtained permit more accurate evaluation of formations traversed by a wellbore in order to achieve better drilling control and to make a direct contribution to exploration of hydrocarbon deposits and the like.
Certain well logs are of the acoustic type, that is to say in which acoustic energy is generated by means of a transmitter and travels through all or part of the formations before reaching the receivers, the received signals being recorded and then processed if necessary, in particular in order to provide the possibility of separating the compressive waves or P waves from the shear waves or S waves.
Among the acoustic logs of primary interest which are worthy of mention are the so-called sonic logs which are recorded only in the delayed mode and logs of the more directly seismic type which produce what is known as a vertical seismic profile or wellbore profile and which are also recorded in the delayed mode.
A sonic log is usually performed by means of a special tool which is lowered into a wellbore, a pulse transmitter (for ultra-short pulses repeated at very short intervals) being provided in the upper portion of said tool and a receiver being provided in its lower portion. The time taken by the wave generated by the pulses to propagate through the adjacent formations and around the borehole is recorded progressively as the tool travels upwards over a layer of constant thickness: an integrator makes it possible to determine the time of travel from the recording time origin.
The vertical seismic profile can be obtained by means of specific tools such as those described in patent applications No. 8 402 895 and No. 8 319 727 filed in the name of the present Applicant.
Although delayed logs are undoubtedly useful even if they entail the need to free the borehole by raising the drilling tool to the surface and replacing it by a logging tool, it is equally useful to produce instantaneous logs if only in order to improve drilling control and to check in real time the characteristics and fluid contents of formations.
Instantaneous well-logging operations which are always performed while drilling is in progress and involve either surface measurements such as, for example, measurement of the differential flow rate of the drilling fluid, of the speed of rotation and/or rate of penetration of the drilling tool, of the hydrocarbon content of the drilling fluid, or hole bottom measurements which are made in the vicinity of the drilling tool and which are raised to the surface by various means including an acoustic transmission in the drilling mud.
In the case of instantaneous logs, it has been proposed to employ as a vibration source, not a specific acoustic transmitter but the drilling tool itself or more precisely its lower end portion which will be designated as a bit for the sake of greater convenience. Roller bits, for example, in fact cut into the bottom working face of a borehole by percussion, the rotation of the cutting roller from one tooth to the next being such as to ensure destruction of the rock.
In French Pat. Nos. 1 587 350, 1 590 327 and its Addition No. 96 617, it is proposed to utilize the vibrational energy which is emitted by the bit and propagates within the drilling tool along the string of drill pipes, whereupon the signal received at the surface at the top portion of the drilling tool is pro
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Katz, L. J., "Drill Bit Location, Guidance by Seismic seen Feasible", Oil & Gas Journal, vol. 78, No. 30, Jul. 1980, (Tulsa, OK), pp. 197-200.
Arens Georges
Gros Pierre
Staron Philippe
Societe Nationale Elf Aquitaine (Production)
Swann Tod
Tarcza Thomas H.
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