Logging method and system for measuring mechanical parameters of

Details Logging method and system for measuring mechanical parameters of Logging method and system for measuring mechanical parameters of

1996-11-25

1998-06-02

Brock, Michael

Measuring and testing

Borehole or drilling

Formation logging

7315216, E21B 4700

Patent

active

057585393

DESCRIPTION:

BRIEF SUMMARY
SUMMARY OF THE INVENTION

The present invention relates to a method of geological exploration of the drilled formations by the obtaining of measurements substantially comparable to the acoustic impedance of the formations crossed through by the borehole.
Measurements are obtained from an acceleration detector placed in the drill string between the rock-breaking bit and mechanical uncoupling means arranged between certain elements of the string. Suitable means for processing the unprocessed acceleration measurements allow the measuring results to be exploited after processing in a way that is similar to the exploitation of a log provided by a conventional "sonic" logging tool, possibly coupled with another logging tool, for example for measuring the density of the formation.
The present invention thus relates to a method of geological exploration of the formations drilled by a drill bit fastened to the end of a drill string, said string comprising measuring means delivering a signal representative of the acceleration created by said bit. Mechanical uncoupling means are placed in the drill string, said measuring means are set between said drill bit and said uncoupling means, and a measurement representative of the acoustic impedance of the drilled formations is obtained by processing said signal by a function of the rotating speed of the bit and of the depth.
The acceleration measurement can be considered in a time window ranging between 5 and 30 s, and said processing can notably consist: acceleration signal, by the rate of penetration raised to a power close to 0.1, constants related to the borehole environment, notably the depth, and Pf is the bottomhole pressure.
The means for measuring the acceleration can include at least one accelerometer placed so as to measure a signal representative of the axial acceleration, i.e. substantially along the axis of the borehole.
The means for measuring the acceleration can include at least one accelerometer placed so as to measure a signal representative of the rotational acceleration. They can include at least one accelerometer placed so as to measure a signal representative of the flexural acceleration. Said accelerometers can have at any time a known orientation in space.
Changes in the nature of the drilled formations can be determined from the variations of said measurement representative of the acoustic impedance.
Changes in the pore pressure of the drilled formations can be deduced from the variations of said measurement representative of the acoustic impedance.
Seismic pickups can be placed at the surface, from which seismic uphole times can be deduced, the source being the noise of the drill bit, for example of the tricone type. In the method, a synthetic seismic response in uphole two-way time can be calculated from said measurement representative of the acoustic impedance and said uphole times.
The invention further relates to a system of geological exploration of formations drilled by a drill bit fastened to the end of a drill string, said string comprising means for measuring a signal representative of an acceleration created by said bit. The system includes mechanical uncoupling means, measuring means placed between the drill bit and said uncoupling means, and means for processing the signal representative of the bit acceleration and delivered by said measuring means. The measuring and/or processing means can include memories for storing the signals.
The uncoupling means can uncouple mechanically the axial motions of the lower part of the drill string from the upper part of the string.
The uncoupling means can uncouple mechanically the rotating motions of the lower part of the string from the upper part of the string.
The system can include means for sending to the ground surface at least part of the signal representative of the bit acceleration.


BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be clear from reading the description hereafter of embodiments given by way of non limitative examples, with reference to

REFERENCES:
patent: 3626482 (1971-12-01), Quichaud et al.
patent: 5372207 (1994-12-01), Naville et al.

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