US2048731A - Method of developing oil fields - Google Patents

Description

' July 28, l936.` H. l.. DOHERTY 2,048,731

A METHOD OF DEVELOPING OIL FIELDS (-f-r/U l original Filed May 22, 1925 2 Sheets-Sheet 1 //Sll /N VENTO/e IIIII Hlfll HENRY oof/ERTY July 28, 1936. H. L. DOHERTY METHOD OF' DEVELOPING OIL FIELDS original Filed May 22, 1925r 2 Sheets-Sheet 2 ff i NN /NVENTo/e f i Y HENRY L. DOHERTY BY /wwd/ ATTORNEY Patented July 28, 1936 UNITED STATES HDMI PATENT OFFICE METHOD oF DEVELoiNG on. FIELDS Henry L. Doherty`,igv York, N. Y.

Original application May 22, 1925, Serial No. 31,996. lDivided and this application October 19, 1932, Serial No. 638,505

2 Claims.

This invention relates to the art of recovering petroleum, and particularly to improved flow control valves adapted for regulating the-inow of oil to well tubing. The present invention was 5 originally described in my copending patent ap- /L plication Serial No. 31,996,-of which this is a g division.

The present methods of production or of extracting oil from the ground are very ineflicient. The accepted estimate of expert geologists and production engineers show that in many localities the present methods of oil production do not recover much more than 20% of the oil in sand. When oil wells are rst put to producing, there is obtained a higher initial production than is obtained later. This high initial production has been primarily attributed to the high gas pressure prevailing in the oil sands at the time the 1, oil wells are rst projected therein, it being well C .0 known,V that the expulsive energy of the gas increases as the square of the pressure. 1' Though it is known that gas pressure is an L lll important controlling influence in drainage of oil sands Aand that every elort should be made by the operator to conserve the gas and permit it to flow from the oil" reservoir only in suicient quantity to secureoil production, it is seldom that the operator has found it to his interest to conserve the gas for the reason that the operator usually has control of but a very limited portion of the oil eld acreage, the surrounding acreage usually being held by other and com- Where the oil eld is coneting operators. g "r trolled by different operators it can be readily 35 appreciated that the operator who first gets his well into the oil body will usually obtain the largest oil production by reason of the fact that the initial production is always higher than later on when the gas pressure has been reduced and 40, the gas dissipated. If the operator of the rst j well projected into the oil body should seek to conserve the gas and to reduce the quantity escaping to that necessary to produce oil, he would be acting against his own interest because by maintaining the back pressure in the well, the gas would be free to carry oil out to the adjacent surrounding wells of competitors.

From the above remarks, it willbe readily appreciated that the ideal method of developing an oil field would be to have the same under the control of one operator or one responsible authority so that proper conservation of the gas and the maintenance of back pressure in the Wells could be maintained to the end that the maximum extraction of the oil from the oil sands would be had.

With the above facts in View it is a primary object of the invention to provide an improved oil recovery apparatus by which a high percentage of oil may be recovered from an oil sand Without the economic Wastes which result from the present method of production.

Another object of the invention is to provide a method of producing oil by which the escape of gas with the oil may be held to minimum.

A still further object of the invention is to provide a method and apparatus by which the gas pressure at the bottom of the well may be determined.

With these and other objects in View the invention consists in the improved methods of and apparatus for developing oil elds hereby de- -scribed and particularly dened in the appended claims.

I have discovered that there is another Very important factor besides the expulsive energy of the compressed gas which determines the amount of oil that ca be extracted from the oil sands. I have found that the viscosity of crude oil Varies indirectly with the amount of natural gas dissolved or absorbed therein,-in 4other Words, the fluidity of the oil varies directly with the amount of gas dissolved or absorbed in the oil. Inasmuch as a less viscous oil moves through the oil sand with less resistance, it can be readily appreciated that the discovery is of the utmost importance and that an additional reason is offered for the conservation of the gas in the oil eld. The dissolved gas also causes a material lowering of the surface tension of the oil.

Referring to the drawings forming part of this specification Fig. 1 is a vertical sectional view diagrammatically illustrating the positioning of wells in an oil :field of the dome type;

Fig. 2 is a chart containing three heavy line curves showing relation between relative viscosity of crude oil containing dissolved gas under pressure and cubic feet of gas dissolved per barrel of oil.

Fig. 3 is a Vertical section through an oil Well showing means for ascertaining the pressure of the gas at the bottom of the well and for regulating the flow of the oil; and

Fig. 4 is an enlarged sectional detail View of the valve mechanism at the bottom of the well above the packer through which the oil and gas must pass before passing up and out through the top of the well.

Util HIUUH As already indicated, I have discovered that the viscosity of the oil is materially lowered depending upon the amount of gas dissolved or absorbed therein. By reference to Fig. 2 it will be seen how the viscosity of the oil varies with the amount of dissolved natural gas therein. Curves a and b are based on the same grade of crude oil but on anatural gas of different methane content. Both curves show that the viscosity decreases as the amount of gas dissolved in the oil increases, and of course the amount of gas which is dissolved in the oil varies directly as the pressure. In curve a themethane content of the natural gas is approximately 52% while in curve by it is approximately 82%. The other constituents of natural gas such as ethaire,W

example, geological structures indicate the position of oil bodies and various types of drilling mechanism together with geological indications assist in locating oil bodies. Actual drilling of a comparatively large area will assist in locating oil bodies, and generallythedenite boundary lines of an oil body are determined by drilling operations. While locating an oil body in accordance with the present invention it is very desirable that the area and boundaries of one or more gas bodies accompanying the oil body, be denitely located. Then the oil horizon or lower boundary should be located to find the position of the water body below the oil body.

Referring to Fig. 1, gas wells lll should be drilled into what would be the top of the dome propane Iand butane are more soluble-infilmoilA 'structure to locate the position 0f the gas bOdy thaifmet''ahdhence render the oil less viscid. In any event it will be seen that the amount of gas dissolved in the oil has a material bearing on its viscosity and hence of the ease with which it will ow through the oil sands. Curve c is based on a differentA grade of crude oil but on Ythe same methane content of the gas as curve b. Curve c shows, therefore, that different oils have a diierent viscosity with the same amount of gas dissolved therein.

Inasmuch as the viscosity of the crude oil is less the greater the amount of gas dissolved therein, it is obvious that it is of rst importance to maintain as nearly as possible the original gas pressure on the oil. Once the gas under pressure is allowed to escape it will be practically impossible to restore the original viscosity even by pumping natural gas back into the oil body because of the impracticability of securing intimate contact of the gas and oil, such contact being necessary to obtain complete absorption of the gas in the oil. In the original crude oil the gas has become thoroughly mixed and absorbed in the As already indicated, the present methods of of the gas pressure and hence to obtain the maximum possible production. When the gas pressure has been allowed to become low by dissipation, the viscosity of the oil has increased and thus its capacity to flow through the oil sands has also been reduced.

The present invention contemplates a method of oil production by which a body of oil is developed as a unit. The development of an oil body as a unit under the present laws requires that the developer own or control all of the surface land under which the oil body is located. In

Imany cases it is not practicable for one party to have control of allv of the surface land under which an oil body is located.- yTherefore, it is anticipated that the increased recovery of oil under the present invention and similar methods and a greater conservation of gas will act to stimulate National and State legislation .which will require that all oil bodies that may be located shall bev developed as a unit for the sake of conservation and economy.

To develop an oil eld in accordance with the present invention it is necessary to locate Vquite definitely the position and boundaries of the oil body. The location of the oil body is usually effected by exploration. The term exploration is intended to include all the common and usual methods being used for locating oil wells. For

above the oil. When these wells are drilled precaution should be taken to keep the wells closed to the end that when the gas body is tapped by the well the gas may not escape and thus the pressure be maintained within the gas sand. Simultaneously with the drilling of the gas wells .10, oil wells l2 should be drilled to determine the -boundaries of the oil body, and flowing wells should be located in the oil body such that the wells will project into the upper portion of the oil body. As the oil wells are drilled they should be kept closed and any oil which might flow through the wells should flow only against a sufcient back pressure to maintain substantially the original oil pressure in the oil sands. Wells i4 should also be drilled to determine the water boundary of the oil pool or body for a purpose .hereinafter mentioned.

As is well known the oil reservoir is usually found between impervious layers of rock, the upper layer being indicated at i6 and the lower Alayer at i8. All of the wells will, therefore, be

projected through the upper layer I6. It is recognized that the dome structure shown in Fig. 1 is an ideal one but whether the oil body be found in a dome structure or in other forms the application of the invention will be substantially the same inasmuch as the relative positions of the gas, oil and water bodies will be substantially the same in all structures. The gas body has been indicated at 20, the oil body at 22 and the underlying water body at 24.

The oil wells and preferably also the gas wells are provided at or near the bottom with an ad- .justable bottom flow bean valve 'diagitmmatically indicated by 26 in Fig. 1. Referringto Figs. 3 and 4 wherein the well and valve structure are illustrated in detail, 28 indicates\the well casing which '36' at its bottomfor a needle valve .38` which is threadedly' mounted in the cap as at 40 by suit- 'ableextensions'leading therefrom. This valve is controlled from the top'ofr the well by a hollow yvalve stem 42, the samev passing through the casing 'head and having a crank or the like 44 for adjusting the valve to its seat. 'I'he valve has an lopening 46 extending axially therethrough so that oil and gas coming'through the packer will pass 70 50 which is located intermediatev the valve stem .and a pump `5L,

Inasmuch asthe valve '38 has an opening extending therethrough and said opening is indirect communication with the hollow valve stem42, the oil from the oil body is free to rise in the hollow valve stern and consequently the gauge 50 will indicate a certain pressure which, however, .will not be the oil pressure existing on the oil body in the oil sands. The pressure indicated by the gauge will be less than the pressure existing on the oil body by an amount equal to the hydrostatic head of the column of oil which has risen in the hollow valve stem. Just what the height of the column of oil in the hollow valve stem is, will be uncertain of determination. If, however, air or gas is pumped into the hollow valve stem by the pump 52 suilcient to drive the oil out of the hollow valve stem, the actual pressure at the bottom of the well can be determined. As gas or air is pumped into the hollow valve stem the pressure on the gauge will rapidly rise as the height of the oil in the valve stem diminishes. When, however, all of the oil has been driven out of the valve stem, the pressure on the gauge will remain substantially constant due to the fact that the air or gas subsequently pumped into the valve stem will be free to enter a reservoir of relatively large cubical capacity and consequently the amount of gas forced into the reservoir by each stroke of the pump will be relatively small as compared with the capacity of the reservoir. It will, therefore be appreciated that the relatively constant pressure indicated by the gauge will be the pressure so regulated that the oil will flow out of the well against a back pressure which `will be somewhat less than that existing in the oil in the oil reservoir. In other words, the oil will pass into a region of somewhat reduced pressure above the valve 38 before passing out through the top of the well and the expulsive force of the expanding gas will carry the oil upwardly and out through the top of the well as will be readily understood.

As the oil is withdrawn from the oil reservoir the pressure of the gas therein will gradually fall. Any drop in pressure, however, will permit dissolved .gas to pass out of the oil from whence it will find its way to the gas body 20 overlying the oil body. It has already been indicated that the viscosity of the oil is less the greater the amount of the dissolved gas therein. This invention therefore contemplates the maintaining of the original pressure or a high pressure approaching the original pressure on the oil body to prevent increase of the viscosity of the oil. This may be accomplished in different ways. A gaseous fluid idsM by Way` ff the K maintalllllgjgbstantially the originalgas preis.,

sure .011.1119 911,

tionto that .of maintaining the original viscosity of the oil is obtained, namely that of preventing oil from the oil body from moving upwardly into thacikdry. sand in which. the gas; bodyxoccurs. Dry gas-sand 'will take up a,comparativelyV 'large amount of oil'fandr'hold the Vsame by capillary attraction so that its Vremoval from the sand by ordinary methods of oil production is impossible. The described method of preventing the oil from moving upward into the dry gas sand is, therefore, an important feature of the invention.

As oil is withdrawn from the oil reservoir its level falls and hence the capacity of the gas chamber above the oil body also increases.` Any increase inthe capacity of the gas chamber is objectionable because it necessitates the pumping of a larger volume of gas into the same to maintain the original gas pressure on the oil body. For this and for other reasons hereinafter appearing the invention contemplates the maintaining of the oil level substantially constant and the -same is accomplished by introducing water into the water wells I! projecting into the oil body. The water is introduced comparatively slowly so as to permit it to. spread under the entire oil area 25 and thus to elevate the oil body as a whole. Furthermore, by introducing the water slowly the tendency for the water to channel through the sands toward the oil wells will be reduced to the minimum. It will also be apparent that if there( is no avenue of escape of water to the outlying sands, the amount of water introduced should equal only the amount of oil drawn 01T from the oilbody.

The water supplied to the water wells will preferablybe the same type of salt water as that which occurs naturally on the oil fields, and this water may be handled through a single pumping station. It will be apparent that only a comparatively low pressure will be required because there are balanced hydrostatic heads in the oil wells and waterwells. The water wells are deep?! than the oil Wells andvdue to the fact that th lpumping the waterinto the wells I4 the only Y'pressure which is required is that pressure 50 which is necessary to overcome the resistance of the flow of water through the oil sand. Furthermore, it will be seen that the deeper the wells the greater will be the advantage of recovering oil by the balanced heads of water and oil because the higher hydrostatic heads of water tend to create a greater pressure for forcing the oil out of the ground. This is very important because by this method itis possible to force oil out of the sands which are very far from the surface of the earth where it is impracticable to remove oil from the wells by pumping due to the mechanical limitations of the ordinary pumping mechaanism.

When water is introduced into the oil sand 65 around the horizon of the oil body it may have to travel many feet or many miles before it will materially affect the pressure of the oil in some portions of the body. However, if the pressure is maintained throughout the oil body and the 70 gas pressure is maintained above the oil body, by a slow gradual process the water may be forced through the oil sand to drive the oil out of the sand through the wells. Furthermore, as the water advances through the sand and past out- 75 lets which formerly served as an outlet for oil, this oil outlet may be used as a water inlet.

There will be a comparatively large number of oil wells as distinguished from water wells, the number of oil wells being such that substantially all parts of the oil body will have an outlet. The water will, preferably, be introduced simultaneously through all of the wells I4 surrounding the oil body and oil may be simultaneously flowed through all or the greater part of the oil wells projecting into the oil body.

I have previously indicated that the origina rock pressure may be maintained on the oil body by introducing gas through the gas Wells l0. It should be pointed out, however, that the introduction of water through the water wells may under certain conditions serve to maintain substantially the original rock pressure on the oil body. This Will become more readily apparent when it is remembered that one factor tending to cause a reduction of the pressure on the oil body is the fact that the capacity of the gas chamber above the oil body increases as the level of the oil falls due to its withdrawal from the oil body. If, however, the level of the oil body is maintained substantially constant by the introduction of water below the oil body, as previously indicated, there will be no reduction of pressure .in the gas chamber from this cause. The only two other factors which would tend to cause a reduction of the pressure in the gas chamber are the dissipation of the gas through the gas wells and the escape of gas with the oil through the oil wells. However, inasmuch as the gas wells are kept closed there will be no ,escape of gas through them. The escape of free gas from the gas chamber by way of the oil Wells will be negligible because of the relatively high back pressure maintained in the oil wells. It will, therefore, be seen that the rock pressure on Y the oil body may be maintained in three different ways; namelyubynintrodugcinggas under pressure throughnthe 'gas or oil wells; by intdi'ihgwater t'onmeet the Aoil body through the water wells, or

45; byernploying both methods simultaneously. Furtlfier, it willbe apparent upon reiiection that those oil wells which are projected farthest into the cil body will eventually begin to flow water as the water level rises, assuming that Water is being introduced below the oil body for the purpose of maintaining its upper level constant. When this occurs such wells will be stopped or may be employed as water wells for the introduction of water. If, on the other hand, no change is made in the water level, some of the oil wells will eventually become gas wells as the oil level falls. These wells will then be stopped or may be utilized for pumping gas into the gas chamber.

From the above description it will be seen that I have provided a method of and apparatus for developing oil ieldswhich will permit the extraction of the maximum amounts of oil from the oil eld and that the invention makes full use of an important property of the original oil, a property which has heretofore not been availed of in the development of oil fields; namely, the property that oil in its original condition in its rock -chamber has a very low viscosity due to the natural gases dissolved therein. As previously indicated, the low viscosity of the oil in the oil body permits it to flow with relatively great freedom through the oil sands.

Another important advantage resulting from the extraction of oil according to the present invention is that the amount of gas produced with each barrel of oil is reduced to a minimum. Other advantages will be apparent to those skilled in the art.

While the invention has been described with considerable particularity of detail, it is to be understood that no limitations on the invention are intended except as may be expressed by he appended claims.

What is claimed as new is:

1. A method of extracting oil from an oil eld having a body of gas overlying a body of oil int .j

an earth cavity, which comprises providing one or more Wells which penetrate the oil body" through which oil may flow to the earths pressure against the oil entering a well suilicient to maintain gas in solution in the oil body as oil .is withdrawn from the cavity, and holdingan iusblbacl; pressure on the oil in the well sufficiently less `than tht held on the'oil entering the well to permitl gas to escape from solution in vthe oil in the Well at a controlled rate thereby Aliberating expulsive energy of the expanding gas for lifting the oil'to thtopof tl"i""well.

2. A method of extracting il from a body of y oil in an earth cavity,'which comprises providing one or more wells which penetrate the oil body through which oil may flow to the earths surface, holding an adjustablgwback pressure against the voil entering a wllsuiiicit'towmaintain gas in solution in the oil body as oil is withdrawn from. the cavity, and holding an adjustable back pressure on the oil in the wells sufficiently less than that held on the oil entering the well to permit gas to escape from solution in the oil in the well at a controlled rate thereby liberating expulsive energy of the expanding gas for lifting the oil to the top of the well.

HENRY L. DOHERTY.

Cil

w X .l (as CERTIFICATE or CORRECTION. Q

Pat. 'ne No. 2,048,731.

HENRY L. DOHERTY.

it is hereby certified that error appears in the printed specification of tie above numbered patent requiring correction as follows: Page 2, second Column, line 52, after the word "bean" insert or; page 4, second column, line 54, claim l, for the article "a" read an adjustable; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 23rd day of February, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.

July 28. 1936.

CERTIFICATE 0F VGRRECTIQN.

ment No. 2,048,731. my 28, 1936.

. HENRY L. DOHERTY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:n Page 2, second column, line 52, after the word .'beanl insert or; page 4, second column, line 54, claim l, for the article "a" read an adjustable; and that the said Letters Patent should be read with these corrections :therein that the same nay conform to the record of the case in the Patent Office.

Signed and sealed this 23rd day of February, A. D. 1937.

Henry Van Arsdale 59:61) Acting Commissioner of Patents.

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