Core sampling method and core sampler therefor

Details Core sampling method and core sampler therefor Core sampling method and core sampler therefor

1998-11-19

2000-12-26

Neuder, William

Boring or penetrating the earth

Boring without earth removal

Combined with earth removal

175 58, E21B 2506

Patent

active

061643890

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a core-sampling method, particularly for the oil industry, comprising core sampling proper using a core sampler comprising at least an inner barrel, an outer barrel and a bit.
It has become apparent that during core sampling and/or during a certain period of time after this operation, some formations to be sampled tend to lose a fairly sizeable proportion of their original properties, particularly their mechanical properties. For example, their cohesion may be altered to a greater or lesser extent. This being the case, it may even happen that part of the core sample is completely destroyed during core sampling. At least some of the information it was hoped to obtain through the operation is therefore lost. In other cases, the formations may tend to disassociate into separate superposed layers, which then present the appearance of a stack of plates, and such core samples do not reflect the true situation and do not have the true parameters of the formation which it is desired to analyze.
The object of the present invention is to solve this problem and to provide a core-sampling method which enables the core sample obtained from these formations to retain properties which are as close as possible to those of the formations in the state which they were in prior to core sampling.
To this end, the core-sampling method of the invention comprises: sample being formed, a substantially axial compression force that is within limits chosen as a function, in particular, of the material of the core sample, and from the inner barrel.
The solution proposed by the present invention to this problem has come as a surprise to those skilled in the art who tend to exert the least possible stress on a core sample while it is being produced, out of fear of damaging it. Numerous and very expensive laboratory trials carried out on formations of diverse natures have been needed in order to establish that the method of the invention solves the aforementioned problem.
According to one embodiment of the invention, the compression force is produced by: against the top of the core sample, the face pressing on the top of the core sample, a fluid which, at least during core sampling, is brought up to a pressure corresponding to the compression force, the form of the compression force being maintained, at least temporarily, on the top of the core sample.
The present invention also relates to a core sampler designed for implementing the method of the invention, and comprising: when considering the direction of progress of the core sampler during core sampling, so as to rotate the bit, for accommodating a core sample, to be able to press against the bottom of a sampling hole and on the top of the core sample which is formed and which penetrates the inner barrel, and a closed end of the inner barrel, situated at the rear end thereof.
According to the invention, the above core sampler further comprises: space so that they can accumulate and restore energy resulting from the pressurizing of the fluid introduced, at least following compression of this fluid by the piston driven into the internal space by the core sample, and in such a way that the fluid introduced into the internal space can escape therefrom as the core sample pushes the piston into it, and so that depending on the leak adjusted, the pressure of the fluid introduced into the internal space increases up to a value that corresponds to a substantially axial compression force applied by the piston to the top of the core sample and which is between limits chosen as a function of the material of the core sample.
According to one embodiment of the invention: piston to the core sample, an auxiliary piston arranged to slide in the internal space and a compressible elastic element, preferably a spring arranged between the piston and the auxiliary piston, and is intended to receive the aforementioned pressure and which is dimensioned to provide at least some of the aforementioned force, the additional part of this force if need be then originating from a fa

REFERENCES:
patent: 2147896 (1939-02-01), Harrington
patent: 2633336 (1953-03-01), Stokes
patent: 2713473 (1955-07-01), Talbot
patent: 3207240 (1965-09-01), Hugel
patent: 3548958 (1970-12-01), Blackwell
patent: 3818997 (1974-06-01), Bridwell
patent: 4479557 (1984-10-01), Park et al.
patent: 5360074 (1994-11-01), Collee et al.

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