US 2942663 A
Description (OCR text may contain errors)
June 28, 1960 w. M. HAGGARD 2,942,663
REDUCING LIQUID LEVEL IN WELL TUBING Filed July 28, 1958 A I? 1* 01K. 7/
20 e A E INVENTOR.
WARD M. HAGGARD ATTORNEY United States Patent REDUCING LI un) LEVEL IN WELL TUBING Ward M. Haggard, Sun Oil Co., P.O. Box 2831, Beaumont, Tex.
Filed July 28, 1958, Ser. No. 751,489
2 Claims. (Cl. 166-45) duction, the hydrostatic head of the wash water in the well tubing often is too great to permit the well to flow. It then becomes necessary to reduce the water level in the tubing sutficiently to allow the well to be brought in. Also, during the producing life of a well, salt water may accumulate in the well tubing until the hydrostatic head exceeds the formation pressure, thus stopping production. Likewise in such cases, it is necessary to lower the water level in the tubing so that flow can again be obtained from the formation.
Various methods are known for reducing the water level in well tubing. One procedure involves providing the tubing at a suitable depth in the well with an unloading valve which can be caused to open by the application of air or other gas pressure at the top of the tubing and thus to allow the water to flow from the tubing into the casing annulus and thence out of the casing at the well head. A procedure of this type which utilizes an unloading valve positioned on the side of the tubing string is described in Hodges application Serial Number 659,873, filed May 17, 1957. Other such procedures employing unloading valves positioned either as a part of the tubing string or in a side pocket mandrel in the tubing string are described in Hodges applications Serial Numbers 746,276 and 746,277, each filed July 2, 1958. These procedures permit water to be removed from well tubing after a packer has been set between the tubing and casing beneath the level at which the unloading valve is located. It is also known to lower the water level in a well before a packer has been set byforcing the water from the bottom of the tubing and thence up the casing annulus.
The usual manner of reducing the liquid level in the tubing, either when it is provided with an unloading valve above a packer or before setting a packer and without an unloading valve, involves merely forcing a gas under sufficient pressure into the top of the tubing until the liquid level has been lowered to the desired depth. However, this generally requires the application of a high pressure due to a progressive increase in the gas pressure necessary at the well head during the unloading operation. The procedure is thus both time consuming and expensive.
The present invention provides an improved method for reducing the liquid level in a well tubing which has a passageway for fluid to flow therefrom into the casing annulus, such passageway being provided either by an unloading valve or the open bottom end of the tubing. The procedure not only permits the unloading to be done ice in considerably less time than heretofore has been possible, but it also permits the use of substantially lower pressures at the well head. This results in a marked reduction in compressor capacity requirements and a corresponding reduction in the costs for carrying'out the operation.
According to the invention the liquid level in a well tubing, which has been provided with an unloading valve located at a depth above the packer but below the maximum depth to which the liquid level is to be displaced or which has no packer and no unloading valve, is first displaced downwardly by forcing a gas into the top of the well tubing. Introduction of the gas is stopped after the liquid level has been lowered only part way to the desired depth. Then liquid is forced into the tubing above the gas column until the level of the liquid below the gas has been reduced to the desired depth. This causes progressive compression of the gas column in the tubing without requiring a corresponding progressive increase in pressure at the well head. At the same time the bulk of the introduced liquid remains, as has now been discovered, as a liquid column above the gas column. After the desired lowering of liquid level has been secured, pressure is released at the top of the tubing. This permits expansion of the gas column which results in lifting of the liquid thereabove from the well.
The invention is more specifically described with referenoe to the accompanying drawing which schematically depicts a well provided with a packer and with valve means for unloading liquid from the well tubing into the casing above the packer.
With reference to the drawing, a well is shown having a casing 10 provided with perforations 11 adjacent a production zone designated as zone A. vWell tubing 12 extends inside the casing and a conventional packer 13 is positioned for sealing the lower part of the casing annulus. Above the packer the tubing string contains a side pocket mandrel 14 adapted to hold an unloading device 15 located adjacent a port 16 in the mandrel wall. The unloading device 15 can be any known or suitable tool of this type containing valve means adapted to open when sufiicient pressure is applied in the tubing and thereby permit flow of fluid through the device and port 16 into the casing annulus. The tubing string may, if desired, be provided with a check valve, indicated schematically at 17, to prevent liquid from being forced back into zone A whenever pressure is applied to the well tubing.
At the well head a compressor 18 is provided for supplying a gas, such as air or natural gas, under pressure to tubing 12 via valve 19 and line 20. Also a pump 21 is provided for supplying liquid, such as water or crude oil, to the tubing through line 22 and valve 23. Additional equipment at the well head includes a pressure gauge 24, a pressure release line 25 having valve 26, and a line '27 containing valve 28 for flow of liquid from the casing.
Whenever it is desired to reduce the liquid level in the tubing 12, compressor 18 is started and air or other gas is forced into the tubing. The increase in pressure therein causes the valve in unloading device 15 to open and admit liquid to the casing annulus, with liquid being withdrawn therefrom through line 27 and valve 28. Preferably the amount of gas forced into the tubing at this stage is at least sufiicient to displace the liquid level downwardly at distance which is at least one-half the total desired length of displacement. Introduction of the gas is stopped, however, substantially before the liquid level has been lowered to the desired depth. After stopping of compressor 18, pump 21 is then started and water or other liquid is forced into the tubing above the gas column. If desired, a separation device may be insorted into the tubing to precede the liquid from pump 21 so as to prevent any mixing of the introduced liquid attained. This required a time of 8 /3 hours.
with the gas. This would be" desirable, for example, it air were used as the gas while crude oil is used as the hquid; or also if for some reason the pressure is not to be released from the tubing until after a considerable lapse of time afterxthe desired displacement level has been reached. However, when employing air and water as'the 7 displacement fluids, no separation device is normally'required forsuccessf ul operation ofthe present method since most of the water' pumped 'in remains above'the air column. 1
After the desired reduction of liquid level has been 'eifected in the above described manner, the pressure on the well tubing is'released by opening valve 26 in line 25. This allows the gas column, which had previously been progressively compressed as the liquid was pumped inabove it; to expand and force the liquid ahead of .it out of the tubing through line 25. Thereafter the well can be brought into production from zone A. The foregoing procedure can be employed in essentially the ,same manner for lowering the waterlevel in well tubing before a packer has been set. i In such case the unloading device 15, check valve 17 and packer 13 would not be present. Gas followed by liquid would be forced into the tubing in the manner described above, thus causing the water'to flow from the bottom of the tubing "and up the casing annulus until the desired amount of water 'hadbeen displaced. Pressure would then be released at the well head to permit the gas column to expand and force out the liquid above it. Thereafter a packer could be set and the well then brought in on production. a
The following specifically illustrates advantages of the invention: V
A well having a 2" tubing required unloading of the V tubing liquid to a :depth of 7800' in order to maintain flow. When this was done in conventional manner'by '3 pumping in'only airusing a compressor rated at 65 cubic feet per minute, the pressure at the top of the tubing had to be progressively increased to V avalue exceeding 3000 psig before the desired lowering ofliquid level was Later, the well was'u'nloaded to the same depth in accordance with the present invention. This was done by first forcing in enough air with the same compressor to reduce the liquid level to 3900'. The pressure at the surface dur- 7 ing this stage built up to a maximum of 1500 p.s.i.g. Water was then pumped into the tubing in amount of approxi- 7 required for this operation was 2 /3 hours as compared to the 8 /3 hours needed when the conventional procedure wasused. 7
I claim: r 1 a 1. Method of removing liquid from well tubing in a cased well where the hydrostatic head of the liquid column is Vsuchthat thewell will'not flow at the desired rate, said well tubing having a-passageway through which liquid can be forced from the tubing into the casing an- "nulus, which comprises introducing a. gas into the top of the tubing to effect liquid flow through said passageway, stopping such introduction of gas when the level of the liquid in the tubing has been lowered only part wayto the desired depth, then introducing a liquid intothe top of the tubing to lower the level of the liquid beneath the gas further while compressing thecoli mn of gas thereabove in the tubing, and thereafter releasing pressure at the top of. the well tubing whereby said column of gas expands and forces the liquidv column 'aboye it out ofthetubing, V V
2, Method vaccording to claim l wherein the amounts "of gas and liquid introduced into the well tubing are such that the length of displacement of saidliquid level during introduction of the. gas is at least as much'as the length of displacement during introduction of the liquid.
References Cited in the file of this patent 2,808,887 Erwin Oct. 8; 1957