US1787972A - Method of developing oil fields - Google Patents

Description

166-25U FIPROli Ill Peseta a, 1931 i unit-en s'rarasrarainr osrica ma L. DOHERTY, or new roan, x. Y.

unrnon or nnvnnornvc on. rmns R0 Drawing. Application filed-11111 20, 1925, Serial No. 44,915. Renewed Kay 20, 1980.

This invention relates to the development of oil fields and more particularly to a method of extracting the oil from the oil bearing sands in such a manner that the expulsive force of the gas usually found with the oil may be utilized to the best advanta e in extracting the oil from the sands and ringing it to the surface.

Unless an oil pool iscontrolled by a single operator, the wells are usually projected into.

the oil sands in a more or less haphazard manner without any particular regard to the character of the oil sands and the other factors governing oil production, each operatpr striving to be the first to get producing wells into the oil sands in order to profit by the flush production which usually follows when the wells are first, entered into the producing sands. In other words, no particular system of control ofthe wells is practiced, each well being allowed to flow from the time it is entered in the oil bearing sands. Where a single operator has control of an oil pool, the method of oil production is not substantially different from that where more than one operator is entitled to enter the field, the

primary difierence being that not so many wells will be sunk in the field. -Ho\ vever, such wells as are sunk in the field are allowed to flow from the time the oil bearing sands have been reached without regard to other wells which may subsequently be drilled into the same sands. As a consequence the percentage of oil recovered from the sands by present methods of oil production falls far short of the percentage which might be recovered if the expulsive force of the gas could be fully utilized.

When a single well is first opened to the flow of oil andgas there is roduced an exccssive amount of gas which 18 due primarily to the fact that gas travels more readily than oil over a large area to a point of decreased pressure; As a result of the excessive production of gas the gas pressure over the entire oil area or horizon declines more rapidly than the amount of oil produced .would warrant.

I have devised a method of. flowing 011 from the oi. sends constituting the oil pool 'ity of each well.

some of the wells may reach the oil produc-' ing sands ahead of others in which event such wells will be shut in for the time being or unt1l all of the wells have-reached the oil producing sands after which the entire group of wells will be opened simultaneously and allowed to flow oil and gas. By developing the field as I propose, that is to say, by opening all of the wells simultaneously, the gas pressure will be exerted on all of the wells and will result in a much greater oil production becauseneither the oil nor gas will have to travel an excessive distance to-the well which is the point of decreased pressureand consequently-the energy of the gas over the field and within the gas will be utilized to best advantage in moving oil to the well. The oil in its natural condition in the sand contains-a large quantity of dissolved gas. the amount of gas dissolved in the oil depending on the rock pressure. As set forth in a pending application I have discovered that oil containing natural gas-in solution has a much lower viscosity than oil which contains nodissolved gas. It therefore follows that the oil in its natural condition is more mobile or fluid than is the case when the gas ress'ure has been released and the dissolv'a gas escaped from the oil. Other conditions being equal the force required to mofii a'viscons liquid through capillary openings such as those which exist in an oil sand varies diicctly with the Viscosity of the fluid.

While the wells are producing, there will be an area of decreased pressure in the vicin- When the wells haw; been producing until the pressure has fallen to a certain point it is proposed to shut-in all the obtained than when they were shut in and this increased production will apply to all of the wells operating in the field. lVhen m the wells are closed in for the purpose of allowing equalization of pressure to take place some of the gas more particularly that which exists in the vicinity of the well where the pressure is low, will be forced back into solution under the increase of pressure.

v It ispreferred to operate the wells under a controlled back pressure so that excessive quantities of gas will not be produced with the oil,the ideal condition being such that thevolume of as produced with each barrel of oil would lie equivalent to the gas dissolved in the oil under naturally occurring.

conditions.

In orderto prevent the ress ure on the field from declining too ra id y it is desirable to returnto the OllSSJld t e natural gas which is being produced with the oil. When the wells are operated under a back pressure, the pressure of the outcoming gas will be comparatively high and it will, therefore, be a comparatively s mple matter to increase or boost the pressure of such gas sufficiently to enable it to be forced or injected into the oil sands. I

v Additional gas taken from nearby fields can also be introduced into the sands while the wells are producing and after they are shut in to enable the pressure on the field to be brought up to the desired point which may be greater or less than the'natural rock pressure. If natural gas is not available air may be used for the same purpose.

the flow of oil tends to decrease quite rapidly and the pressure drops very rapidly after afield has been producing efor sometime, theeeonomic cost of pumping gas may be so high that it will not be advisable to pump into the producing sand sufiicient gas to raise the oil to the original rock pressure. Under such conditions the pressure would be be raised by introducing gas only to a point suf- -ficient to hold a desirable viscosity of the oil and to maintainthe production. A gradual drop in pressure can be continued until all of the oil has been removed that is capable of being removed by flowing under. the pres sure of the oil and gas in the sand- The back ressure which should be kept on the wells will depend upon various factors among which may be mentioned the porosity so of the sands in which the oil and gas occur. In order to determine what back pressure should be maintained samples of the sands will be obtained and these samples subjected to laboratory tests to determine among other 85 things the rate of migration of the oil and gas through the sands under pressures approximatil-ig. those in the oilfield and what differential pressure should be maintained to produce the proper flow ofoil, the tests being made with samples of oil and gas taken from the same field. The cores of the bores taken from the oil sand should be watched very carefully to be sure that the well opens into the most order to give t 1e oil the advantage of migration through the most orous portion.

Another factor which has an important bearingon the back pressure which should be kept u )onthe wells is the extent of reduction o .the pressure which must be given in order to set free the potential energy of the gas in the oil. This pressure reduction preferably should be made as suddenly as possible in order to start a movement or etfervescence of the gas in the oil. This efiervescence or boiling of the gas tends to convert the orous portion of the sand in oil into a foamy mass and carry the oil as foam toward the outlets of the well. If the pressure is reduced gradually the gas will come out of the oil without much effervescence. It is desirable therefore that the pressure changes should be manipulated so-that as much etfervescing or bubbling of the oil can be obtained as possible. This eifervescnce should take plaw not only at the opening ofthe well but back through the sands as far as practicable. Where there are a large numberof openings an subject to the same pressure, the foamy oily mass has a better op ortum'ty to reach a point of low pressure. e

back pressure is maintained at the-top of the well to prevent waste and to conserve the energy of the gas and oil. The highest 3- sible back ressure should be maintain at the top of t o well in order to mcover gas at high pressure so that this high pressure 5 may be returned to the oil sands. The big or the pressure of the gas recovered at the easing heed the less power will be required in compressing itin order to raise its pres sure sufficiently high to force it back into the sand. Accordingly the. pressure at the easing head may be reduced to substantially atmospheric pressure at the time the wells are opened, in order to start the eilervescence or the sudden release of the gas from the 011 Hill and then the back premure may be built up as the other wells or are shut in alto ethen Furthermore if some of the wells shoul cease flowing oil such wells would be shut in.

In addition toll-1e gas which goes back into solution in the oil on accountof the equalization of pressure, the increased pressure resultting from forcinggas into the sands will cause additional volumes of gas to go into solution in-the oil and thereby further increase its fluidity. Also there is obtained a greatcr,expulsivc force when the oil wellsare again opened due to the increased pressure in the vicinity of'the wells.

From the foregoing description it will lie .readily appreciated that a simple and practical method of producing oil is provided,-

' a. method which enables the. pressure of the gas on-the field to be utilized in a n2c-t efiective manner in the production of oil.

What is claimed is:

1 A method of'developing an oil field comprising projecting a plurality of wells into an oil sand, preventing flow of gas and oil from any given well until all of the wells are ready for producingand then flowing the oil and gas from all the wells simultaneously.

2. A method of developing an oilfield comprising projecting a plurality of wells into an oil sand, preventing flow of gas and oil from any given well until all of the wells are ready for producing and then flowing the oil and gas from substantially all the wells simultaneously under a hack-pressure.

3. Inthe method of claim 2 the steps of opera ting oil wells under a uniform backpressure and periodically reducing the pressure qually on all of the wells simultaneously. 4. 'A method of developing an oil field coinprising projecting a plurality of wells into an oil sand, preventing flow of gas and. oil. from any given well until all of the wells are ready i'or producing, then flowing the oil and gas from substantially all thewells simultaneously, and shutting in any well .which subsequently flows more gas than other wells. 5. In the method of claim 1 the steps com prising allowing 'all of the wells to flow oiland gas until the gas pressure falls to a-predetermined point, thereafter shutting in all of the wells until theprc-ssure remaining inthe sands has equalized over the entire lield,

and again opening the wells.

6. In'thc method of claim 1 the steps comprising allowing all of the wells to flow oil and gas until the as pressure falls toa predetermined mint. thereafter shuttim in all of the wells and restoring pressure over the entire oil area by injecting a gaseous fluid into the oil sands." v

7. A method of developing an oil field comprising projecting a plurality of wells into an oil sand, allowing all of the wells to flow oil and gas "under a back-pressure until the gas pressure falls to a predetermi-nedpoint and then shutting in the wells, pumping a gaseous fluid into the held to bring the pressure in the oil sands up to a. predetermined simultaneously.

8; A method of dcvelopin an oil liehl.

.point, and again opening all o l the wells comprising projectin a plurality of Wcllsjnto an oil sand and a lowing all. of the wells natural gas coming from the flowing wells, shutting in the wells when the gas pressure falls to a predetermined point, pumping into the field. a gaseous fluid under pressure until to flow oil'and gas,.restoring to the field the the pressure in the field has reached a prcdetermined-poi at, and the wells.

9. In the method of claim- 2, the steps of maintaining such back-pressure on the wells a ain 0 nin all of that substantially the same ratio between oil and gas flowing from the wells is maintained at all of the wells. r c

10. A method of developing an oil field comprising projecting a plurality of wells into an 011 sand, maintaining such back-pressure' on the wells that an antiallylhe same ratio between oil and gas flowingfrom the well is maintained at all of the wells, and

shutting in such wells as produce an excess ofgas. 11. maintaining such back pressure on the well thatsnhstantially the same production ratio between oil and gas is maintained 'at all of the wells, shutting in the wells when the gas pressure reaches a predetermined point and allowing thpressure in thefiel; to equalize;

. 12.- In the method of claim '2, the steps of maintaining such back pressure on each of the wells thatsubstantially the same production ratio between oiland gas is maintained at all of the wells, shutting in such 'wells'as produce an excess amount of gas, and increasing the pressure in the oil sands by pumping a gaseous fluid, into the field.-

13. In the method of claim 2,- the steps of In the method 0t claim 2, the steps of maintaining a controlled back-pre sure on the wells such that a definite Ill-()(hlCLiJll ratio between oil and gas is maintained at each of the wells, restoringtothe field the natural gas flowing from the wells, and shutting in any well which produces an excess quantity of it. A method of develo aing an oil field III! comprising projecting a urality of wells into an oil sand, maintaining such hack-pres ,sure on each of-the wells that a substantially duction ratio between oil and gas is main: ta'ined at all of the wells, restoring to the field the natural gas flowing from the wells, Shutting in any well which produces an excess quantity of gas, finally shuttin'g in all of the wells, increasing the pressure over the entire field lay-pumping into the same a gaseous fluid under pressure, and thereafter opening all of v the wells andallowing them to flow under a back-pressure. r 16. A methodpf developing a new oil field comprising pro ecting a plurality of wells into an oil bearing sand, opening the wells to the flow of oil and gas; allowing the wells to flow until more gas is flowing than would ordinarily flow if only that gas which is dissolved in the oil constitute the expulsive force, shutting in the wells, increasing the gas pressure in the fieldsufiiciently to redissolve the natural gas in the oil in the oil sand, and thereafter opening the wells simultaneously to the further flow of oil and gas.

17. A methodofdevelopinga new oil field comprising pro ecting a. plurality of wells into an oil sand in spaced relation throughout substantially the entire oil sand area,

preventing flow of oil from any of the wells until all the wells are ready for production,-

and opening all of the wells simultaneously 'to the flow of oil and gas.

In testimony, whereof I afiix m signature. HENRY L. DOfiERTYL