Production Of Oil From A Pumping Well And A Flowing Well

Abstract

Production of oil from a pumping well and a flowing well wherein gas which is produced in the pumping well is conveyed to and utilized to facilitate production of oil from the flowing well. Flow from the flowing well may be initiated by pumping a light oil into the annulus. The method may be utilized with wells produced by fire flooding.

Description

This invention relates to the recovery of oil from a subterranean oil-bearing stratum. More particularly, this invention relates to producing oil from wells by a gas lift system.

It is appreciated in the art that frequently higher oil production can be achieved by flowing a well rather than by pumping a well. Thus, for example, a comparison between pumping and flowing a typical oil-producing well is tabulated below: ##SPC1##

Because of the advantages of flowing a well it has been heretofore proposed to produce wells by employing a gas lift system. It is a principal object of this invention to provide a new and improved process for producing oil utilizing a gas lift technique.

SUMMARY OF THE INVENTION

Oil is produced from both a pumping well and a flowing well by a process wherein gas which is produced in the pumping well is conveyed to the flowing well to assist in the flowing thereof.

The oil production process of this invention is described in detail in conjunction with the accompanying drawings in which:

FIG. I is a schematic drawing showing one arrangement of apparatus for producing oil in accordance with the invention.

FIG. II is a schematic drawing showing arrangement of apparatus for producing oil in accordance with another embodiment of the invention.

Referring to FIG. I, well 10 penetrates an earth formation 11 in which there is located an oil-bearing stratum 12. The well is provided with a casing 14 and a tubing string 16, the upper portion of which is joined to the production or flow line 17. The casing 14 and tubing string 16 form annulus 18. Pump 20, suspended on rod 19, is disposed within the lower portion of tubing 16. By means of pump 20 oil is pumped to the surface and recovered via line 17. Pumping is preferably conducted at a rate sufficient to maintain the oil level in the well at substantially the depth of pump 20. The oil enters the well 10 through perforations 23 in the lower portion of casing 14.

Gas which is produced with the oil flows up annulus 18 and is sent via conduit 24 to a second well 26. The gas flows down into well 26 through annulus 28 which is formed between casing 29 and tubing 30. In this manner the gas intermingles with the oil within well 26, thereby "aerating" or lightening the oil and carrying it to the surface through tubing 30 and through recovery or flow line 32. The gas used in the gas lift system requires no compression and as long as the pressure at the bottom of the tubing 30 in flowing well 26 is equal or less than the pressure at pump in pumping well 10, there is no increase in the bottom hole pressure in well 10 and there is no restriction in oil production therefrom. However, even if the bottom hole pressure in pumping well 10 does increase to some extent, the increased oil recovery from flowing well 26 generally results in an overall increase in oil production from wells 10 and 26.

This method of oil production possesses considerable flexibility. Thus, a number of pumping wells can be connected to one or more flowing wells. The method is particularly advantageous for use in connection with wells which are produced by means of fire flooding or in situ combustion processes since in such instances a high gas to oil ratio exists due to formation of carbon dioxide. At the same time, in the flowing well 26 a high gas-oil ratio is maintained so that the pressure at the bottom of the well is low resulting in what is referred to as "good drawdown." The expression "good drawdown" refers to a condition where the bore hole pressure is such as to facilitate greater oil flow into the bore hole.

FIG. II of the drawing shows apparatus for producing oil by the method of this invention and wherein oil flow from a flowing well is initiated or "kicked off" by use of a light oil such as diesel oil. In this embodiment of the invention pumping well 40 penetrates earth formation 41 in which there is an oil-bearing stratum 42. Well 40 is provided with casing 44 and tubing 46 with annulus 48 being formed therebetween. Pump 50 is suspended on rod 51 to a depth near the oil-producing stratum 42. By means of pump 50 oil is pumped to the surface and recovered via line 53. Pumping is preferably conducted at a rate sufficient to maintain the oil level in well 40 at substantially the depth of pump 50 but not to permit produced gas to flow up tubing 46.

Conduit 54 connects annulus 48 with a second well 56 which is to be flowed rather than pumped. Well 56 is provided with casing 58 and tubing 60 with annulus 62 being formed therebetween. Since the casings of pumping well 40 and flowing well 56 are connected by means of conduit 54, the casing pressure in both wells will build up to a value substantially equivalent to the reservoir pressure with both being filled with gas.

Before initiating flow from well 56, valve 93 is opened so that the liquid level in tubing 60 will fall to the liquid level in annulus 62. This level is the same as the oil level in well 40. Valve 93 is then closed. Next a light oil such as diesel oil from storage tank 66 is pumped by high pressure pump 68 through line 70 into annulus 62 in well 56. The light oil is pumped into annulus 62 at a moderate rate, say of from 300 to 700 barrels per day. After sufficient light oil has been pumped into well 56 to displace the oil or water back into formation 42, valve 86 is opened to initiate flow from tubing 60 through line 76 and into a low-pressure separator 80 in which the light oil is separated from other materials which may be present therewith. The light oil separated in separator 80 is recycled via line 82 into storage tank 66 while volatile materials can be vented through line 83. Control valves 85 and 86 are employed to control flow through conduits 74 and 76 respectively.

Pumping of the light oil into annulus 62 is continued until natural flow from well 56 is established or until the viscosity of the returning oil increases significantly due to mixing with the produced crude oil. At this time pump 68 is shut down and the oil and gas flowing up the tubing will usually be diverted directly to oil recovery conduit 74 by closing valve 86 and opening valve 85. However, if natural flow is not well established it will sometimes be desirable to continue production to low-pressure separator 80. This is done by using transfer pump 91 to pump oil from the storage tank 66 through conduit 90 to oil recovery conduit 74.

In accordance with the invention, gas produced in well 40 flows via line 54 controlled by valve 92 into the annulus 62 of well 56. The gas so introduced mixes with the oil in well 56 thereby exerting an aerating or lightening effect and stimulating flow up through tubing 60 and through oil recovery line 74.

In some wells natural flow can be more readily initiated if 50 to 200 barrels of light oil are pumped into formation 42 before valve 86 is opened to flow the well.

Again, when this invention is utilized with wells produced by fire flooding the gas introduced into annulus 62 via line 54 will contain a substantial amount of carbon dioxide. The light oil, such as diesel oil, which is introduced into well 56 will absorb carbon dioxide. When pressure is released, i.e., when high pressure pump 68 is shut down, carbon dioxide comes out of solution reducing the density of the oil and facilitating flow of well 56 through tubing 60. Moreover, even before well 56 starts to flow some of the carbonated light oil may be displaced into the earth formation thereby stimulating initial productivity. Likewise, after the well starts to flow the carbonated light oil in annulus 62 mixes with the produced crude oil thereby reducing its viscosity and aiding flow.

Those modifications and equivalents which fall within the spirit of the invention are to be considered a part thereof.

Claims

I claim:

1. A process for producing oil from a pumping well which penetrates a gas and oil-bearing subterranean stratum and a flowing well which penetrates an oil-bearing subterranean stratum, each of said wells provided with a casing and production tubing, which process comprises establishing the liquid level in said flowing well at the liquid level in said pumping well, introducing a light oil into the annulus of said flowing well, recovering said light oil from the tubing of said flowing well, passing said light oil to a separation zone in which it is separated from accompanying materials, recycling the separated light oil from the separation zone to a storage tank, pumping oil up the tubing of said pumping well and passing gas produced in said pumping well to said flowing well to comingle with fluids produced therein and to facilitate flow of such fluids from said flowing well.