Measuring and testing – Borehole or drilling – Downhole test
Patent
1980-11-27
1982-09-07
Myracle, Jerry W.
Measuring and testing
Borehole or drilling
Downhole test
175 40, E21B 4900
Patent
active
043477364
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to the technology of drilling boreholes or wells, and more particularly it relates to the methods of continuously logging a well or borehole being drilled.
The invention can be employed to utmost effectiveness in geological survey work when prospecting survey wells.
The invention can be also effectively used in natural fuel gas and oil production for determining the lithological properties of the rock traversed by a production well being drilled.
BACKGROUND ART
At present, the lithological composition of a rock being drilled is determined by obtaining a sample of the rock by a core bit and subsequently analysing the texture and mineralogical composition of the rock. This technique is characterized by its time- and labour-consuming character, and, hence, by its high cost.
There are also widely known methods of determining the tectonics, structure and lithology of rock with aid of electric-logging charts obtained by conducting electric logging while drilling a borehole or well. The methods are likewise characterized by their highly labour-consuming character, because in order to conduct the logging, the drilling tool has to be pulled out of the borehole, the appropriate instruments have to be run into borehole on the cable, and the data obtained has to be subsequently interpreted and analysed.
There are further known methods of determining the lithological composition of the rock in a borehole by using the drilling cuttings entrained in the upward flow of the drilling mud. The drilling cuttings are employed according to these methods for determining the texture and the mineralogical composition of the rock strata traversed by the borehole, by using laboratory methods.
However, these last-mentioned known methods are characterized by the insufficiently accurate information they yield, since it cannot be always positively known to which traversed stratum these or other drilling cuttings belong, to say nothing of the considerable time it takes to investigate the mineralogical composition of the samples of the drilling cuttings.
DISCLOSURE OF THE INVENTION
The present invention has for its aim the creating of a continuous borehole-logging method, wherein the physical parameter used should enable to determine the lithological composition of the rock strata traversed by the borehole in a rapid, accurate and relatively simple manner.
This aim is attained in a continuous borehole-logging method in the course of drilling with the use of a drilling mud, which method, in accordance with the invention, includes subjecting the drilling mud fed into the borehole to unipolar electric treatment, while measuring its oxidation-reduction potential and maintaining this value substantially permanent at a given magnitude; continuously measuring the value of the oxidation-reduction potential of the drilling mud returning from the borehole and comparing this value with the given value of the oxidation-reduction potential of the drilling mud fed into the borehole, and using the difference between the two values at any given moment to determine the mineralogical composition of the rock adjacent to the bottom of the borehole by comparing said difference with the known in advance normal oxidation-reduction potentials of minerals.
The proposed method enables to enhance the accuracy of the determination of the lithological composition of the rock, owing to the direct contact of the rock with the drilling mud being accompanied by processes of ion exchange therebetween, such processes altering the major parameters of the drilling mud, and of its oxidation-reduction or redox potential, in particular.
Furthermore, the proposed method enables to simplify and speed up the determination of the lithological composition of the rock, eliminating as it does such labor-consuming operations as taking core samples or sampling the drilling cuttings, as well as the operations involved in electric logging of boreholes.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described in connection wi
REFERENCES:
patent: 3722606 (1973-03-01), Fertl et al.
patent: 3802259 (1974-04-01), Eckels
Alekhin Stanislav A.
Bakhir Tatyana M.
Bakhir Vitold M.
Mamadzhanov Ulmas D.
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