Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Patent
1997-03-13
1998-05-19
Porta, David P.
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
250361R, G01T 120, G01V 506
Patent
active
057539197
DESCRIPTION:
BRIEF SUMMARY
This invention relates generally to a gamma ray detection and measurement device which is intended to detect the presence of gamma ray emissions and to provide a measurement of the level of emissions.
The invention has been developed primarily to provide a measuring device or tool which can be used to measure the level of gamma ray emissions in a stratum which is being drilled i.e. to carry out gamma ray monitoring during drilling, in which case the device follows the drill bit fairly closely--typically being located between 1 and 50 feet above the drill bit, depending on the configuration of the drill-string and on the presence or absence of a drilling motor. Therefore the device has to be designed to be sufficiently robust to withstand the conditions prevailing in such an arduous environment i.e. temperature, pressure, vibration and shock loadings. Not only must the device be sufficiently robust or "ruggedised" to withstand these conditions without damage, but also it must be sufficiently sensitive so as to detect and measure relatively low levels of gamma ray emission while being exposed to these conditions.
Measurement-while-drilling (MWD) is a technique used during oil and gas well drilling to acquire data from instruments located near the drill-bit and transmit this data to the surface, as shown schematically in FIG. 1. The principal problems to be overcome are the survival of the instruments in an extremely hostile environment (temperature, pressure, shock and vibration) and the transmission of data from a location which is often thousands of meters below the surface of the earth.
There are several solutions to the transmission problem. The method most commonly used, shown schematically in FIG. 1 is to employ a device 1 near the instruments 2 which can in some way influence the circulation pressure drop of the usual drilling fluid which is employed. The consequent disturbances in fluid pressure can then be detected at the earth' surfacesby a suitable pressure transducer 3. Using a suitable coding scheme, data can be transmitted as pressure pulses, or variation in pressure pulses in the fluid column running up to the surface and then, for example, be decoded in an appropriate computer system 4. These basic techniques are well-known to those of ordinary skill in the art.
There are many useful measurements which can be made, but the most significant are the inclination to the vertical and also the compass heading of the bore hole which is being drilled. With this knowledge, the hole which is being drilled can be steered towards a specific target, without having to interrupt the drilling process to lower survey instruments down the well.
A second class of measurements which are carried out is related to the properties of the rock which is being drilled, and its hydrocarbon-bearing potential. It may also be useful to make engineering measurements at the bit, for example the applied load and the rotary torque.
One particularly useful measurement which can be carried out in an MWD technique is the measurement of the presence, and the level, of gamma ray emissions from various layers through which the drill bit is guided e.g. layers of shale, and sand-stone, since different types of layer give predictable levels of gamma ray emission. Even layers of the same material, but of different properties, can have different but predictable levels of gamma ray emission. Therefore, it is known to provide a downhole detector for measuring natural gamma ray emission, and one of the purposes of this measurement is to make a deduction about the type of rock or layer which is being drilled, by looking at the total gamma ray intensity, or at the spectral energy distribution of the gamma radiation, in the bore hole at the detector location. Another purpose is to correlate the sequence of rock formations with those which have already been determined in a nearby borehole. FIG. 1 shows schematically a gamma ray detector 5 which in this case is mounted above a drilling motor or other component of the drill string 6. The basic pr
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Knight John H.
Prain Kenneth A.
Geolink (UK) Limited
Porta David P.
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