US1899497A - Method of developing oil fields - Google Patents

Description

Feb- 28 1933- H. L. DOHERTY 1,899,497

IE'IIiOI) OF DEVELOPING OIL FIELDS Filed Mayv 22, 1925 2 Sheets-Sheet l la 2o 3o 4o l l CU. F7.' GAS D/ssoLl/ED P/SR BBL. O/l.

HENK y L. DOHERTY S14/vento@ l Feb. 28, 1933. H. L.' DOHERTY IETHOD 0F DEVELOPING OIL FIELDS 2 Sheets-Sheet z Patented Feb. 1933 UNITED STATES HENRY L. DOHERTY, F NEW YORK, N. Y.

METHOD OF DEVELOIING OIL FIELDS Application led May 22, 1925. Serial No. 31,996.

This invention relates to an improved method of developing oil fields, aLl-more particularly to a'method of extracting oil from an oil field-from which no oil has previously been removed. v

The present methodsv of production or of extracting oil from the ground are very ineflicient.v The accepted estimate of expert geologists and production engineers show that in many localities the present methods of oil production do not recovermuch more than 20% of the oil in sand.

lVhen oil wells are first put to producing, there is obtained a higher initial production than is obtained later. This high initial roduction has been primarily attribute to the high gas pressure prevailing in the oil sands at the time the oil wells are first projected therein, it being well known that the expulsive energy of the gas increases as the square of the pressure.

Though it is known that gas pressure is an important controlling infiuence in drainage of oil sands and that every effort should be made by the operator to conserve the gas and permit it to flow from the oil reservoir only initial production is always higher'than later. 40 on when the gas pressure has been reduced andthe gas dissipated. If the operator of the first well projected into the oil body should seek to conserve the gas'and to reduce the quantity escaping to that necessary to pro-l duce oil, he would be acting against his own interest because vby maintaining -the back pressure in the Well, the as would be free to carry oil out to the adacent surrounding wells of competitors.

From the above remarks, it will be 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 method of oil production 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 by which oil may be produced simultaneously over the entire area or the major area of the oil body. J l

Another-'object of the invention yis to pro- 70 vide a method of producing oil by which the escape of gas lwith the oil may be held to minimum.

A still further object of the invention is to provide Y-a. method and apparatus by which the gas pressure at the bottom of the well may be determined.- l r I With theseand'other objects in view the invention consists in the improved methods of developing oil fields hereby described and particularly defined 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 can 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 other words, the fluidity of the 90 oil varies directly with `the amount of gas dissolved-or absorbed inthe oil. Inasmuch as a less viscuous oil movs 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 o'ered for the conservation of the gas in the oil field. The dissolved gas also causes a material lowering of the surfacel tension of the oil.

Referring to the drawings forming part of this specification: y

Fig. l 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.

As already indicated, I Ahave discovered that the viscosityof the oil is materially lowered depending upon the amount of gas dissolved or absorbed therein.l By reference to Fig. 2 it will be seen how the yviscosity 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 a natural 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 the methane content of the natural gas is approximately 52% while in curve b it is approximately 82%. The other constituents of natural gas such as ethane, propane and butane are more soluble in the oil than methane and hence render the oil less viscid. In any event it will be seen that the amount of gas dissolved in the oil has a ma# terial bearing on its viscosity and hence of the ease with which it will flow through the oil sands. Curve c is based onl a different grade of crude oil but on the same methane content of the gas as cu ve Curve c shows, therefore, that different oils have a different viscosity with the same amount of gas dissolved therein. y

Inasmuch as the viscosity of the crude oil is less thel greater the amount of gas dissolved therein, it is obvious that it is of first 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 pumpingl 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 oil during the long period of time during which the oil and gas have beeny in Contact and by the movements which have taken place between them while in the oil reservoir.

As already indicated, 'the present methods of oil production are not conducive to a conservation of the gas pressure and hence to obtain the maximum possible production. IVhen 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 abody 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 many cases it is not practicable for one party to have control of all of the surface land under which an oil body is located. Therefore, 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 be developed as a unit for the sake-of conservation and economy.

To develop an oil field in accordance with the present invention it is necessary to locate quite 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 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 com.- paratively large area will assist in locating oil bodies, and generally the definite 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 definitely 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. l gas Wells l0 should be drilled into what would be the top of the dome structure to locate the position of the gas body above the oil. Vhen 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.y 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 wlich might flow throu h the wells should flow only against a suillgcient back pressure to maintain substantially the original oil pressure in the oil sands. Wellsl4 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 16 and the lower layer at 18. All of the wells will, therefore, be projected through the upper layer 16. It is recognized that the dome structure shown in Fi .l1 is an ideal one but whether the oil body e 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 andthe underlying water body at 24.

The oil wells and preferably also the gas wells are provided at or near the bottom with a valve dlagrammatically indicated by 26 in Fig. 1. Referring to Figs. 3 and 4 wherein the'well and valve structure are illustrated in detail, 28 indicates the well casing, 30 the casing head, with associated valve mechanism, and 32 a packer at the bottom of the well. At the top of the packer is secured a sleeve-like cap 34 having a valve seat 36 at its bottom for a needle valve 38 which is threadedly mounted in the cap as at 40 by suitable extensions leading therefrom. This valve is controlled from the top of the well by a hollow valve stem 42, the same passin through the casing head and having a cran or the like 44 for adjusting the valve to its seat. The valve has an opening 46 extending axially therethrough so that oil and gas coming through the packer will pass through the valve and into the valve stem. The valve stem exteriorly of the casing head is con` stem 442, the oil from the oil body is freeto thanv the pressure existing on the oil body by' an amount equal to the hydrostatic vheadlof the column of oil Awhich has risen in the hol- ...low valve stem. l Just what the height of the column of oil inthe hollow valve stem is, will be uncertain of determination. If, however, 'air'jor gasis pumped into the hollow valve stem by the pump 52 suiiici'entto drive the oil out of the hollow valve stem, the actual pressure atthe bottom of the well can be determined. As gas or air is pumped into the hollow valve stem the'pressure on the gau e will rapidly rise as the height of the oil 1n the valve stem diminishes. When, however, al=` of the oil has been driven out of the valve stem, the pressure ori 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 as forced into the reservoir by each stroke o 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 existing on the oil in its reservoir.

The pressure on the oil having been ascertained as aforesaid, the valve 38 is o ened,

whereupon oil and the dissolved gas wi l pass through lateral openings 54 above the valve seat and into the well. The valves in the casing head are then so regulated that the oil 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 thereon wlll gradually fall. Any dropfinpressure, however, will permit dissolved gasto pass out of the oil from whence it will find its way to the gas body 20 overlying the oil body.y It has already been indicated that the viscosity of the oi. 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 ody to prevent increase of the viscosity of the oil. This may be accomplished in different ways. A gaseous luid,preferably natural as, may be pumped directly into the gas through the gas wells which project into the same or it may be pumped into the oil sands by way of the oilwells. The natural gas pumpedinto the earth cavity in which the oil and gas are found, will preferably be that which escapes from the flowing oil wells,4

though if necessary, natural gas from -other sources may beused. Natural gas is pre-vv v ferred to air because I have found that with some oils air seems to increase the viscosity of the oil and moreover air introduces certain complicationsin the processes of obtaining natural gasoline from the gas.- By maintain- .ing substantially vthe original gas pressure on.

the oil body, another advantage in addition to that of maintaining theoriginal viscosity of the oil is obtained, namely, that of preventing oil from the oil body from moving upwardly into the oil dry sand in which the gas body, occurs. Dry gas-sand will take up a comparatively large amount of oil and hold the same'by capillary attraction so that its removal 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 in the 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 0f the oil level substantially constant and the same is accomplished by introducing water into the water wells 14 projecting into the water body below the oil body. The water is introduced comparatively slowly so as to permit it to spread under the entire oil area 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 oif from the oil body.

T he water supplied to the water Wells will preferably be 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 onlya comparatively low pressure will be required because there are balanced hydrostatic heads in the oil Wells and Water wells. The water wells are deeper than the oil wells and due to the fact that the water has a higher specific gravity than the oil, there would be a natural tendency for the oil to be forced out of the sands through the oil wells if the resistance of the flow of Water through t-he oil sands were not too high. Therefore in pumping the water into the wells 14 the only pressure which is required is that pressure which is necessary to overcome the resis-.tance of the How 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 lground. This is very important because by this meth-uI it is 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 mechanism.

When water is introduced into the oil sand 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 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 outlets which formerly served as an outlet for oil, this oil outlet mav 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 14 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. 0

I have previously indicated that the original rock pressure may be maintained on the oil body by introducing gas through the gas wells 10. 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 ofthe 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.v It will,therefore, be seen that the rock pressure on the oil body may be maintained in three different ways; namely by introducing gas under pressure through the gas or oil wells; by introducing w^ater to meet the oil body through the water wells, or by employbe stopped or may be employed as water wells -t'or 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 developing oil fields which will permit the extraction of the maximum amounts of oil from the oil field 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. y

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 the appended claims.

W'hat is claimed as new is:

1. A method of extracting oil from a virgin oil field comprising treating the field as a unit, providing one or more wells which penetrate the oil body underlying the field and through which oil may flow to the surface, maintaining a body of gas under pressure above the oil body, and compensating for the oil withdrawn from the field by introducing to the field below the oil an equivalent amount of water under pressure sufficient to maintain the upper oil levelA substantially constant.

2. A method of extracting oil from a virgin field comprising treating the fieldvas a unit, providing one or more wells which penetrate the oil body underlying the field and through which oil may fiow to the surface, maintaining a body of gas under pressure above the oil body, compensating for the as withdrawn from the field by introducing thereinto an e uivalent amount of gas, and

compensating or the oil withdrawn therefrom by introducing thereinto below the oil pensating for the gas Withdrawn from the field with the oil by introducing an equivalent amount of gas into the field'.

L A method of extracting oil from a virgin oil4 field comprising treating the field as a unit, providing one or more wells which penetrate the oil body underlying the field and through which oil may flow to the surface, maintaining the field under substantially its original high gas pressure while removing the oil through said wells, holding a back pressure on the wells below but approximating the gas pressure in the field, compensating for the gas withdrawn from the field by introducing thereinto an equivalent amount of gas, and compensating for the oil Withdrawn therefrom by introducing thereinto below the oil an equivalent amount of water.

5. A method of extracting oil from a vir- I original pressure thereon, and flowing the oil from said field into said wells against a back pressure.

6. The method of extracting oil from a virgin oil field which consists in projecting an oil well into the oil field, maintaining substantially the original viscosity of the oil in the field by maintaining in the oil substantially the original amount of dissolved gas and permitting the oil to fiow from the field against a back pressure ymaintained near the bottom of the well.

7. A method of extracting oil from a virgin oil field operated as a unit, which comprises providing one or more wells which penetrate the oil body underlying the field and through which oil may flow to the surface, removing oil through said wells under a back pressure below but approximating the gas pressure in the'field, and gradually elevating the bottom level of the oil body as its volume is diminished by introducing water therebeneath under a hydrostatic head suflicient to colnter balance the head of oil in said oil we s.

8. In combination, an oil well having closure means at its top, a packer adjacent the bottom of thewell, a valve in the packer, said valve having an opening through which oil below the packer may pass upwardly, a hollow valve stem extending from the opening in said valve up and through said closure means, pressure indicating` means connected to t-he hollow valve stem, and means for sup- 10 plying a pressure medium through the valve stem and valve and means for opening said valve to permit oil from the oil body to escape into that portion of the well above the packer. In testimony whereof I afix my signature. HENRY L. DOHERTY.

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