US 2573390 A
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Description (OCR text may contain errors)
Oct. 30, 1951 BLANCHARD 2,573,390
GAS DETECTOR Filed July 11, 1946 ff ii IN V EN TOR.
A DkE BLANCl-MRD BY W, W) fa ATTORNEYS released into the atmosphere.
Patented a. 30, 1951 GAS DETECTOR Andr Blanchard, Houston,".lex., assignor to Schlumberger Well Surveying Corporation, Houston, Ten, a corporation of Delaware Application July 11, 1946, Serial No. 882,961
The present invention relates to apparatus for detecting the presence of gas in a liquid. More specifically, it relates to a new and improved apparatus for detecting the presence of gas in the drilling mud which is customarilyused to facilitate drilling operations in the oil industry.
It is the usual practice in drilling oil wells by the rotarymethod to circulate a water or oil base drilling mud in the bore hole, which serves both as a coolant and for bringing the drill cuttings to the surface. When the drill penetrates into a gas bearing sand during the course of drilling operations, a quantity of the gas enters the drilling mud stream and is carried to the surface with the drill cuttings. The presence of this gas in the drilling mud isa detriment to proper operation since it tends to lighten the weight of the mud column and thus increase the danger of a blowout. For this reason, it is highly desirable for the driller to know when the drill has reached a gas bearing formation, in order that he may take steps to increase the density of the drilling 2 Claims. (01. 13- 19) mud until the hydrostatic pressure of the mud I a gas bearing formation does not result in any considerable continuous flow of gas into the drilling mud stream. On the contrary, the amount of gas entering the mud stream is generally only slightly more than is present in the part of the formation removed by the drill. This gas is carried to the'surface where it expands and is Since it is relatively-small in quantity and is given off only during a relatively short period of time, it is difflcult to detect. It is entirely possible, therefore, for the drill to traverse a gas zone without the q the drilling mud in an oil well, for example.
A'further object of the invention is, to provide va method and apparatus of the above character inwhich the properties of compressional waves are utilized for providing indications of the presence of gas in the drilling mud.
' Another object of the invention is; to provide a novel gas detecting apparatus of the above character which is adapted to operate automatically and unattended to provide a continuous record of gas content versus time or drill depth, and/or to actuate a warning signal when the gas content in the drilling mud exceeds a safe amount.
In accordance with the invention, the presence of gas in the drilling mud of an oil well is detected by transmitting compressional wave energy through the drilling mud stream at the surface and observing the attenuation of such wave energy produced by varying amounts of gas contained in the drilling mud. More specifically, the invention comprises the steps of producing wave energy, preferably but not necessarily in the acoustic range, at a submerged point in the mud stream, and obtaining at another submerged point in the ,mud stream indications of the wave energy transmitted through the liquid between the two points.
It has been determined that the eificiencyof propagation of compressional waves through a liquid is greatly influenced by the presence of gas in the liquid. It has been found that the presence of even a small amount of gas in the liquid results in a marked reduction in the ability of the liquid to transmit wave energy. Other conditions being fixed, the amount of absorption or attenuation of the acoustic wave energy is related to the volume of the gas carried in the liquid. In general, the greater the percentage volume of the gas, the poorer will be the transmission of acoustic waves by the liquid.
Since the acoustic wave transmission properties of the liquid depend on the percentage volume of the gas contained therein, it will be apparent that gas detectors relying on absorption or attenuation of wave energy for their operation are not suitable for lowering in deep bore holes. In deep oil wells, the ambient pressure is invariably very high so that the greater portion of any gas present is in its liquid phase, and only a small portion is in the gaseous phase. For this reason, it is proposed, according to the present invention, to detect the presence of gas in the drilling mud at the surface or very near the point of exit of the mud stream, where the major portion of the gas in the mud stream is in the gaseous phase.
tion of a drill in a bore hole, showing the maninsure that a asvaaoc ner in which the drilling mud is circulated through the bore hole, and
Figure 2 is .a view in perspective of apparatus constructed according to the invention for detecting the presence of gas in the drilling mud.
In Figure l, a conventional type drilling apparatus I is shown in a bore hole ll. Drilling mud is pumped by suitable pumping apparatus (not shown) through the drill pipe I2 to the drilling head II where it flows into the bore hole In through the openings I4. tings from the bottom of the bore hole It are carried by the mud to the top of the bore hole where they flow through a trough or conduit l5 into'a sump l6 from which the mud is recirculated through the bore hole It. Gas detecting apparatus D constructed according to the invention is submerged in the mud in the trough I5 at the surface of the earth, so that the mud stream flows through it.
Referring now to the Figure 2, the gas de-a tecting apparatus D comprises an open-ended cylindrical conduit submerged in the mud stream flowing through the trough IS. A source of acoustical energy It such as a vibrating dia- The drill cut-- 2,451,797 and 578,531, now abandoned, filed Ibbe ruary 17,1946.
In operation, the conduit l1 andlassociated transmitter l8 and receiver 2. are submerged in the mud stream in the trough ll (Figure 1) such that at least a representative partof flow passes'continuously through the conduit 'l'l and the conduit I1 is maintained full'of fluid.
The ends'of the conduit I! may bejilared and quite readily.
The transmitter II is then energized at a constant frequency and power level by the oscillator 19, thereby creating acoustical wave energy that'is propagated through the drilling mud to the receiver 2.. The more gas thereis present in the mud, the less will be the energy that is=received at the receiver 2|. The output $01 the receiver 20, which is a function of the acoustical energy impinging upon it, is amplified, if neephragm, for example, is positioned in oneside of the conduit II. The acoustical energy source It may be energized by any suitable source such as a fixed frequency oscillator Is, for example.
essary. by theampliner 2|. The output of the amplifier 2| may be change to direct current.
by the rectifier 22 and may be recorded birecording meter :23. The concentration of gas present in the drilling mud may be re'adilyde termined by comparing the readingsof the meter-2l with a previously prepared calibration The oscillator l9 may'include any suitable number of power amplifier stages as required to pro-,- duce a high enough energy level for proper op-, eration. A receiver 20, which may be another microphone, is placed a short distance, from three inches to two feet, for example, from the adjusted to operatefat the meter transmitter l8. The receiver 20 may be positioned within the conduit l1 orin an opposite wall thereof, as shown. Preferably the receiver 2|! is positioned so that it will face thetransmitter It, in which case it will receivemaximum energy therefrom.
Indications of the intensity of the acoustical energy received by receiver 20 may be obtained in any conventional manner. One of many possible indicating systems may comprise, for example. an amplifier 2| which receivesthe output of the receiver 20, the output of which may be indicated by a suitable alternating current meter. If desired, the .output of the amplifier 2| may be changed to a variable direct current by a conventional detector or rectifier 22, the magnitude of the signal being indicated on presence of relatively'small quantities of a direct current meter 23. In a field unit, the a meter 23 will usually be, of the recording ,type. Any conventional alarm or warning means may be connected in the output circuit such as in series or in parallel \vithvthe meter '23, and adjusted so that the alarm will sound whenthe -output is less than a predetermined value.
The conduit II should preferably be constructed of a material which absorbs sound the units It and 2|] should be suchas to peri mit their operation while submerged in the drilling mud. If microphones orheadphone units are employed, they may be encased in a thin rubber jacket. Preferably, the acoustical generator should be of 'the type disclosed in the co-pending patent applications of Andre Blanchard, Serial Nos. 578,529, now Patent No.
chartwhich gives meter readings versus different known mixtures of drilling mud and gas; If the danger point gas concentration has been determined, the alarm or warning device maybe reading corre sponding to :this critical value.
Itwill be apparent from the foregoingthat the invention provides a highly satisfactory apparatus for detecting the presence of oil in drilling muds. By determining the absorption or attenuation of compressional wave energy propagated 4 through the; mud; stream near thesurface of the earth,-in"accordance with the invention, the v I" i the drilling mud, can be readily detected.
Other suitable devices for creating. the acoustic wave energy of constant, intensity, and other means for indicating the intensity of the acoustical energy received, will be readily apparent to those skilled in the art, the specific apparatm' shown-being. onlyssehematic and typical. There,- fore, the novel apparatus disclosed herein'should', I be considered as illustrative of the invention and. scope of the appended claims. I
1. Apparatus for detecting the presence of gas in the circulating drilling mudqstream in an oil well comprising an open-ended conduit sub- ..merged in said mud stream at the surface of not as limiting the I claim: 7
the earth and disposed so as to facilitate the flow of said mud stream therethrough, a compressional wave energy transmitter mounted at one side of said conduit, a constant intensity source of wave energy for said transmitter, a compressional wave energy receiver mounted at. another side of said conduit in the path of wave energy transmitted from said transmitter through the mud stream, and means responsive to the output of said wave energyreceiver.
2. Apparatus for detecting the presence of gas a in the circulating drilling mud stream in an oil well comprising an open-endedconduit submerged in said mud stream at the surface of.
the earth and disposed so as to facilitate the flow of said mud stream therethrough, a coinpressional wave energy transmitter mounted at rectifying means and providing a warning signal 4 when the output of said wave energy receiver reaches a predetermined value.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED s'ra'rss mfrrm'rs' Number Name Date 1,570,781 Ruben Jan. 26, 1926 1,935,445 Heinz Nov. 14, 1933 2,214,674 Hayward Sept. 10, 1940 OTHER REFERENCES Book, Ultra Sonics, Bergman and Hatfield, John Wiley 8; Sons, N. Y., publishers, 1938 (pgs. 131, 132).
. Book, Supersonics, Robert Wood, published by Brown University, Providence, R. edition.