US2112845A - Apparatus for locating hydrocarbon deposits in the earth - Google Patents

Description

April 5, 1938. G. HOV-VELL 2,112,845

APPARATUS FOR LOCATING HYDROCARBON DEPOSITS IN THE EARTH Filed Dec. 2'7, 1934.

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/36/// 5 I W 'L 7 1: n illEQz myamu Patented Apr. 5, 1938 PATENT OFFICE APPARATUS FOR LOCATING HYDROCAR- BON DEPOSITS IN THE EARTH Lynn G. Howell, Houston, Tex., assig'nor to Standard Oil Development Company, a corporation of Delaware Application December 2'7, 1934, Serial No. 759,373

1 Claim.

This invention-relates to the location of deposits of hydrocarbon material such as petroleum oil, natural gas or the like beneath the surface of the ground. Deposits of petroleum oil and/or natural gas usually occur in underground strata under considerable pressure. The overlying formations of the ground are permeable to the diffusion of the hydrocarbons from the stratum containing the deposit with a result that the soil gases contain measurable amounts of ethane and sometimes butane and propane. It has been customary in prospecting for oil by such geophysical methods as the seismic, gravitational, magnetic and electrical methods to have for an objective the finding of underground structures favorable to the accumulation of 011.

It is an object of the present invention to locate oil or natural gas directly.

Other objects will be apparent from the specification and from the accompanying drawing in which latter- Fig. 1 is a vertical sectional view through the ground showing the apparatus in sectional view;

Fig. 2 is a transverse sectional view taken along the line II]I of Fig. 1; and

Fig. 3 is a vertical sectional view through a modified form of the apparatus in operative position with respect to the ground.

Referring particularly to the drawing, reference numerals I, I designate the surface of the ground containing a bore hole 2 The hole 2 is preferably drilled to a depth of approximately ll feet beneath the surface of the ground in the territory to be investigated. A tubular member 5 is disposed in the hole 2 with its bottom wall 6 disposed in spaced relation to the bottom of the hole 2 to form a reservoir .1, the walls of which constitute the earth stratum 9 in which the hole 2 is disposed. The wall 6 of the tubular member 5 is provided with an opening i I. A conduit l2 extends into the tubular member 5 on the surface of the earth and forms a fluid tight joint with the opening II. An annular collar I5 is secured in fluid tight relation to the upper end of the tubular member 5 and is provided with downwardly extending annular flange l6 which protrudes into the surface of the ground I, I when the tubular member 5 is in position in the hole 2 to form a seal around the tubular member 5 to prevent air from being drawn into the hole 2 from the atmosphere. An additional seal is provided around the hole by means of plaster of Paris or the like, which is poured around the flanged collar l5 to form a seal I8 for the hole.

Soil gases are sucked out of, the ground in the vicinity of the reservoir .1 through the following arrangement of parts: A suction pump 23 is provided with an inlet pipe 24 which opens into the upper portion of a container 26 through a suitable sealing means 21. Ethyl alcohol or other suitable absorbent. for hydrocarbons well known in the art is disposed in the container 26 to a level 29 below the inlet of the pipe 24. Glass beads 30 or other similar solid particles are disposedin the body of liquid in the container 26. The conduit l2 opens into the container 25 below the normal level of liquid in the container. Suction applied by the pump 23 draws the soil gases from the reservoir 1 through the pipe i2 into the body of ethyl alcohol or the like in the container 25. The soil gases bubble through the ethyl alcohol whereby the hydrocarbons become dissolved in the solvent and are retained in thecontainer 26 while hydrocarbon free soil gases are, discharged through the pipe 24. The glass beads reduce the size of the bubbles passing through the solvent thereby giving the hydrocarbons a better opportunity to dissolve in the solvent. If desired, a syphon arrangement or any other means for withdrawing soil gases from the reservoir 1 can besubstltuted for the pump 23 and some of the advantages of the invention will be retained.

In carrying out the pumping operation according to the preferred procedure, a large amount of soil gases is withdrawn from the ground surrounding the reservoir 1- and is passed through the hydrocarbon solvent; for example, approximately 400 gallons of soil gases are extracted from the ground during a period which may constitute four days and four nights of continuous pumping. A partial vacuum is formed in the hole I which prevents faster pumping.

The solvent containing the absorbed hydrocarbons is subjected to analysis for the primary purpose of identifying and determining the percentage of ethane in the soil gases. Soil gases adjacent a stratum containing petroleum oil and/or natural gas contain measurable amounts of methane, ethane and sometimes butane and propane. Ethane is present in the soil gases above oil and/ or natural gas deposits in a concentration of one part in several million parts of soil gas. Also, traces only of ethane or no ethane at all have been found in areas where tube wells have been drilled to salt water and where therefore it is reasonable to conclude there are no oil or natural gas deposits. The end product 01' or: ganic decay is methane. Consequently, methane is found everywhere in varying amounts. It is seentherefore that the positive identification of ethane in a gas sample obtained from the soil is an indication of the presence of a deposit of oil or natural gas below the point at which the gas sample was obtained.

The hydrocarbons absorbed in the solvent are therefore analyzed for hydrocarbons heavier than methane, more particularly ethane and possibly butane and propane. In one method of analyzing the hydrocarbons the ethyl alcohol is subjected to elevated temperatures until the gases dissolved in the alcohol have been evaporated. These gases are then cooled to about -40 C. whereby some of 'the gases are liquefied and this liquid is drained off. The liquid is mostly alcohol but some of the heavier hydrocarbons if present will also liquefy at this temperature. The remaining gases are then cooled of! below the boiling point of ethane (whichis -90 C.). The liquid ethane is then drained oil and measured.

In making a survey, the bore holes 2 may be disposed approximately 500 to 1500 feet apart,

although greater and smaller separations may be employed in different areas. Reconnaissance surveys using the greater separation of bore holes have been found advisable. Those areas which are found to have soils of high hydrocarbon and especially ethane content are then worked in greater detail with the bore holes closer together.

. Referring to Fig. 3, a modified form of the invention is shown in which I, l designate the surface of the ground. A tubular member 35 is provided with an open end adapted to be forced into the ground for a sufllcient distance to form good contact all around the end of the tubular member 35 with the ground. The upper end of the tubular member 35 is closed as indicated at 36 forming a reservoir 31 which opens upon the ground. As shown in its preferred embodiment, the tubular member 35 has the form of a bell jar. Preferably it has a diameter of from three to five feet. A convenient method of sealing it with respect to the ground is to rotate the tubular member until it makes good contact with the ground. Plaster of Paris or other suitable sealv ing means designated 39 is then poured around means illustrated in Fig. 1 and like reference numerals are applied to like parts. The means comprises a pump 23 having an inlet pipe 24 which opens into the upper portion of a container 26, partially filled with suitable solvent or hydrocarbons such as ethyl alcohol. Glass beads 30 or the like are disposed in the solvent. A pipe l2 protrudes into the reservoir 31 at one end and at its other end opens into the container 25 below the level of the solvent therein.

' It will beunderstood that other methods of analyzing gas samples can be used and some of the advantages of the invention will be retained. For example, the gas samples can be subjected to:

1. Fractional distillation by means of liquid air.

Combustion. Positive, or canal, ray analysis. Spectral analysis. High frequency analysis. Magneto-optic method. Allison. The first two methods mentioned above are well QUIDWN known in chemical laboratories. They sufler from the serious disadvantages that rather large samples are required and the sensitivity is low. It is impossible by these methods to work with an accuracy much greater than 0.1 of 1%. Thus ethane must be present to the extent of one part in about 1,000 parts of gas. Soil gas samples rarely contain such an abundance of ethane.

The third method of analysis by means of canal or positive rays permits of the definite identification of the different hydrocarbons in the sample and of estimating their relative abundancies. In this method the gas molecules are shot at a photographic plate by means of an electric accelerating field through crossed electric and magnetic fields. The molecules suffer a deflection in both fields, the deflection in the electric field being proportional to and in the magnetic field 2 1 111? where e=elementary charge E=electric field strength m=molecular weight H=magnetic field strength v=velocity of molecule Molecules of the same molecular weight are focused on the same spot on the photographic plate. The resolution is very high, being about one part in one thousand parts. This means that particles having weights of 100.0 and 100.1, respectively, can be separated. In the present case, the molecular weight of methane is 16.04, of ethane 30.06, of propane 44.08 and of butane 58.10. The relative amount of each constituent of the sample is estimated from the intensities of the different spots or lines on the photographic plate.

The emission or absorption spectral analysis can also be used to detect the presence of the hydrocarbons in the soil gases.

The fifth method is based on the fact that the dielectric constants of these gases are markedly different and that they also have different magnetic susceptibilities. Furthermore, the dielectric constants increase in the order air, methane, ethane, propane, butane, while the magnetic susceptibilities decrease in the same order. It is seen therefore that if a sample of air were placed between the plates of a condenser and inside the coil of an'electric oscillating system tuned to a certain high frequency, say one or several million cycles, the frequency of the system would be higher if methane were substituted for the air, and progressively higher for ethane, propane and butane. The circuit comprising this condenser and coil can be caused to beat against another crystal controlled circuit. Assuming now that the crystal controlled circuit be caused to oscillate at five million cycles and that the first circuit be tuned to the same frequency when air has been placed between the condenser plates and inside of the coil, it is easy to see that the accuracy would be as great as one part in five million, since a beat frequency of one cycle per second could be observed easily. If, therefore, the substitution of the soil gas sample for the air would change the frequency of the circuit by one cycle, the change could be observed. It is known also that the ratio of methane to ethane in natural gas is about eight to one. The apparatus can therefore be calibrated with samples known to contain certain amounts of methane and ethane.

Another highly desirable method is the magnet0optic due to F. Allison. It is possible to detect one part in one hundred billion by means of this arrangement. The method which is described in the literature, for instance in Physical Review, volume 30, page 66, 1927, volume 31, page 313, 1928, and volume 35 page 124, 1930, and elsewhere, is based on the time lag differences of the Faraday efiect behind the magnetic field in liquids as a function of the chemical compounds dissolved in the liquid. The soil gases are passed through alcohol. '.'I'he hydrocarbons are soluble in the alcohol while oxygen and nitrogen are insoluble. The alcohol solution containing the dissolved hydrocarbons is then analyzed. Each chemical compound produces a characteristic minimum of light intensity at a certain length of light path. These minima disappear when the concentration is less than one part in one hundred billion parts. Since ethane is present in the soil gases over deposits of oil and/or natural gas in greater concentrations, it is seen that the magneto-optic method is amply sensitive for its positive identification.

Various-changes may be made within the scope of the appended claims in which it is desired to claim all novelty inherent in the invention as broadly as the prior art permits.

I claim:

In gas extraction apparatus, a tubular mem ber filling the bore of a hole in the surface soil of the earth and having a wall extending across its lower end, a tubular casing surrounding the member having a downwardly extending open end embedded in the earth and a closed end cooperating with the tubular member for sealing the member in the bore, and a conduit opening through the wall and adapted to be connected to a source of suction whereby soil gases can be drawn into the conduit.

LYNN G. HOWELL.

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