US2784677A - Gas anchor - Google Patents

Description

Mmm B29 E957 w. P. mmm-mm2 mm MW GAS ANCHOR Fild Aug. V6 1953 Smets-Sheet l TTRNE'Y zwYAmmw mm; @EMM mmm.. z... @FMEA /m @im B, F Mmmm J n N L p55@ j VN Mmmm HZ E957 Lm. P. mEncHERTZ afa-AL mw GAS ANCHOR Filed Aug. 17, 1953 2 Sheets-Sheet 2 Fi?, yE

i PAUL F E.U:.1F11LE.'1=TZ El I f EARL H .1' EANJJEEHG DA1-,1L An EDNNALLY JH.,

y TEHEN/:E A; FDLLAHD Y i JNVENToRs ATTDHNEY GAS ANCHOR Paul P. Reichertz, Dallas, Carl R. Sandberg, Grand Prairie, and Carl A. Connally, Jr., and Terence A. Pollard, Dallas, Tex., assignors, by mesne assignments, to Socony Mobil Oil Company, Inc., a corporation of New York Application August 17, 1953, Serial No. 374,762

'7 Claims. (Cl. 10S-203) This invention relates to the` separation of gas from gas-liquid mixtures on a continuous basis and relates more specifically to a bottom hole gas anchor employed in oil weils.

in earth formations where petroleum oil is found, the petroleum oil is frequently intimately associated with gas, which causes considerable diliculty in those instances where the oil has to be pumped from the well. The gas occupies a part of the displacement volume of the pump, reducing the volumetric eciency of the pump, and, if present in sufdcient quantities, will cause a complete cessation of the delivery of oil by the pump.

The entrained gas may exist in the form of free gas in bubbles of various sizes. These bubbles of free gas have a rate of rise in a gas-liquid mixture which is a function of the size of the bubbles. The larger the bubbles, the more rapidly they rise in a gas-liquid mixture. The gas anchors which are in general use depend upon this characteristic of the gas bubbles for their success in opera tion. The conventional type gas anchor consists of a chamber in which fluids must tlow downward for some distance in order to enter an opening to a pump intake port. The gas which separates in the chamber of the anchor escapes through ports provided near the top of the chamber. In this type anchor the separation of the gas is dependent upon the bubbles of gas rising at a rate faster than the downward rate of flow of the gas-liquid mixture in the anchor chamber. Small bubbles of gas whose rate of rise is equal to or less than the downward rate of the gas-liquid mixture will not be separated by this type anchor. As considerable quantities of gas are encountered in the form of small bubbles having a low rate of rise, there is a definite need for a gas anchor which will separate these small bubbles.

ln addition to preventing gas entering the oil pump, `it is also desirable to prevent solid particles entering the pump and causing damage to it.

lt is an object of this invention to provide a gas an-` chor which will separate from gas-liquid mixtures gas in the form of small bubbles which cannot be separated by the usual type of gas anchor. this invention to provide a means of increasing the volumetric efcency of subsurface oil `well pumps in those instances wherein gas entering the pump is a significant factor contributing to decreased efficiency of pumping. lt is a further object of this invention to prevent entry into the pump of solid particles which would damage the working parts of the pump. These and further objects of this invention will be understood from the following description of the invention taken in connection with the accompanying drawings in which:

Fig. l is a view in section of a gas anchor constructed in accordance with one embodiment of `the invention. Fig. 2 is an enlarged view in section of the lower end of the porous tube of a modified version of t-he gas anchor shown in Fig. 1. Fig. 3 is a view partially in section and partially in elevation of a gas anchor constructed in accordance with another embodiment of the invention.

It is another object of i ICC In the drawings 1 represents the wall of an oil well or the casing of an oil well adjacent to an oil-producing formation. A cylindrical anchor shell 2 is closed at its lower end by internally threaded collar 3 and externally threaded bull plug 4. Collar 3 is pressed into the lower end of anchor shell 2 and welded in place as shown. Bull plug 4 is threadedly engaged within collar 3. Near its upper end, anchor shell 2 contains a plurality of ports 5 for entry of a gas-liquid mixture and a plurality of ports 6 for escape from anchor shell 2 of separated gas. Welded to the upper end of anchor shell 2 is internally threaded collar 7. Bushing or coupling 3, which is internally and externally threaded and forms a central iiow channel for liquids, is threadedly engaged to collar 7. t will be recognized here that, if desired, bushing 8 could be secured directly to the upper portion of anchor shell 2, thus dispensing with collar 7. Secured to the lower portion of bushing 8 is an eduction tube which comprises swag 9, pipe 10, collar 11, swag l2, collar 13, porous tubes 14 and 15 and bull plug lo, and forms an exclusive path for flow of liquids into bushing 8. Swag 9, which contains external threads on its lower end, is pressed into the lower portion of bushing tl and welded in place. Pipe 10, externally threaded at both ends, is secured to the lower end of swag 9 by internally threaded collar 11, and swag 12, which is externally threaded at its upper end, is secured to the lower end of pipe liti by internally threaded collar i3. Porous tube lid is securedto the lower end of swag l2, and porous tube l5 is secured to the lower end oftube 14j Attached to the lower end of tube 15 is bull plug 16.

ln the embodiment of the invention shown in Fig. 2

the gas anchor of Fig. l has been modified by provid ing a pressure release valve in the bull plug lo at the lower end of porous tube 15. Referring to Fig. 2, the pressure release valveli! is secured within bull plug lo which, in this form of the invention, has a port ld positioned in its lower end. Pressure release valve i7 is designed to open when a predetermined pressure drop across the walls of the porous `tubes is exceeded. When pressure release valve 17 is open, well fluids ow upward into the inside of the porous tubes and out of the anchor through pipe lil. Thus, it can be seen that, in this embodiment, the porous tubes will function unless the flow of iuids through them is impeded by the plugging of their pores or by `the collection of solid matter on the outer surface of the tubes, and in that event the anchor will function as does a conventional anchor. This feature is of advantage in those instances where it is not desirable to cease pumping in the event the porous tubes cease to function. The anchor may be removed for cleaning whenever it is convenient to do so and need not be removed if the eciency of the porous tubes is materially reduced or they become inoperative.

ln the embodiment of the invention shown in Fig. 3, shell i9 s secured tothe lower end of collar 7 by Welding.` Shell 19, which functions to protect the porous tubes from damage while the gas anchor is being installed or removed from awell, is constructed in the form of a hollow cylinder having a large number of 'openings or perforations 20 therein. Theseopenings or per forations Ztl are sufficient in number and size to present negligible impedance to the iiow of well fluids to the po rous tubes. In another embodiment `of the invention, not shown, protection may be provided the porous tubes by using, in lieu of shell i9, a wire framework positioned in spaced relation about the porous tubes and secured at its upper end to the lower end of collar 7. These last mentioned forms of construction are used where it is desirable to allow large gas bubbles, which would normally separate as the well fluids initially enter the anchor, to

rise past the porous tubes to; aid in agglomerating orf` removing the small gas bubbles accumulating on the outer walls of the porous tubes.

It will be evident from the above that in those instances where threads or welding are used to join various members other recognized means of joining metal parts may be used if desired. Thread connections are preferable where used in the interest of easy assembly and disassembly for purposes of cleaning and replacing broken or Worn parts.

The porous material of the tubes operates much more efficiently as a filter if it is presaturated with the liquid it is to pass. In oil wells, water is usually produced to some extent, so porous tube 14 is provided for the purpose of passing oil while porous tube 15 is provided for the purpose of passing water. Before the anchor is put into operation, each of these tubes is presaturated with the liquid it is to pass. In order to lter from the gas liquid mixture the portion of gas which would be detrimental to the pumping operation yet not have an excessive amount of gas released from solution, it is necessary that the pressure drop across the walls of the porous tubes be as small as practicable, with the upper limit not being more than one pound per square inch.

The proper dimensions of the tubes and the proper permeability of the porous material must be utilized to limit the pressure drop across the tube walls to less than one poundper square inch. For satisfactory gas separation the permeability of the porous material should be limited to a range of from one to thirty darcies. Also, the dimensions and permeability of tubes 14 and 15 must be so related to each other that the pressure drop across the walls of both tubes will be the same for the oil-water ratio existing in the well in which the anchor is being used. This is necessary to prevent any tendency on the part of the porous tubes tol cause either water or oil to accumulate within the anchor. The relationship of the factors involved in determining the permeability and size of the porous tubes is expressed in an equation for the flow of fluids through porous media known as Darcys equation, a form of which is oMLn@ where:

P=uid pressure drop across the walls of the porous tube inpounds per square inch.

Q=quantity of uid flowing through the porous tube in barrels per day.

rizinner radius of porous tube in inches.

r0=outer radius of porous tube in inches.

M :viscosity of flowing fluid in centipoises.

L=length of porous tube in inches.

K=permeability of the porous material in darcies.

. The factor 10.66 is a conversion factor to make the equation consistent for the units used.

P, as stated previously, must be limited to one pound per square inch or less. Q, the quantity of uid flowing through the porous tube, may be maintained a constant. M, the viscosity of iiowing fluid, for the oil will vary depending upon the oil being produced, while the M for the water is nearlyk enough a constant that it may be taken as the same for all wells. L, the length of the porous tube, may be varied as needed, although it should not be so great that the tubes are too fragile and ditlicult to handle. K, the permeability of the porous material, as stated above, `should be chosen in the range between one to thirty darcies for satisfactory gas separation. The upper limit of the outer radius, ro, is determined by the size tube Which may be used in the well. The thickness of the tube walls, ro-ri, may be varied as needed to achieve the desired pressure drop across the walls, keeping in mind thatv they must not be made so small as to Oil production- 50 barrels per day Water productionbarrels per day Oil viscosity at bottom hole conditions-25 centipoises Water viscosity at bottom hole conditions--one centipoise Assume use of porous material of following specifications:

For oil-30 darcy permeability, inner radius one inch,

outer radius 11A; inches.

For water-two darcy permeability, inner radius one inch,

outer radius 1% inches. Y

Limit the pressure drop across the walls of the porous tube to 0.1 pound per square inch.

Based upon these well conditions and assumptions, the length of the tube for oil flow is:

= 83.6 Vinches and the length of the tube for Water is:

L=10-66Xm l 0l inches The porous material of which tubes 14 and 15 are made may be sintered metal, Alundum, Aloxite, or other porous materials which have the desired permeability, can withstand well conditions, and may be worked into the desired form and size. If sintered metal is used, it may be manufactured from powdered metals such as brass or stainless steel, which are not subject to corrosion due to contact with the various gases and fluids encountered in oil wells.

Prior to using the gas anchor, the porous tubes 14 and 15 are saturated with oil and Water, respectively. The anchor is then assembled, attached below a deep Well oil pump to a producing string by means of bushing o and lowered to the producing zone in an oil well. Upon the starting of the pump the gas-liquid mixture ows into the anchor through ports 5 and then flows downward within shell 2. The larger bubbles of gas will separate and pass out through ports 6 as the mixture flows downward in the anchor. The mixture containing the small bubbles of gas flows toward the porous tubes. The oil ows through tube 14 and the water through tube 15, the small gas bubbles being separated from the oil and water by the filtering action of the tubes. The small bubbles collect on the outer surface of the tubes, agglomerato into larger bubbles of gas, and pass up the anchor and out through ports 6 in shell Z.

lIf the pores of the porous tubes become clogged with solid particles in the well fluids or the surfaces of the tubes become covered with solids, the pump may be raised from its seat to allow the fluids in the pumping string to ow back through the anchor and `flush out the tubes.

Although the porous material used in this embodiment `of the invention is in the form of tubes, it will be apparent that it may be used in numerous other forms.

Having thus described our invention, it will be understood that such` ydescription has been given by way of illustration and example `and not by way of limitation, reference for the latter purpose being had `to the appended claims;

We claim:

1. In a gas anchor the combination of an eduction tube, at least a portion of which is composed of porous material having a permeability of between one and thirty darcies, and means for securing said eduction tub-e to a producing string.

2. In a gas anchor the combination of a liquid eduction tube, at least a portion of which is composed of a porous material having a permeability between one and thirty darcies, a pressure release valve positioned in the lower end of said eduction tube, and means for securing said eduction tube to a producing string.

3. In a gas anchor the combination of a tubular member closed at its lower end and containing a plurality of ports near its upper end, means for connecting said tubular member to a producing string, a liquid eduction tube closed at its lower end positioned in spaced relation within said tubular member and secured at the upper end thereof to said last-mentioned means, at least a portion -of `said eduction tube being composed of a porous material having a permeability between one and thirty darcies.

4. In a gas anchor the combination of a tubular member rclosed at its lower end and containing a plurality of ports near its upper end, means for connecting said tubular member to a producing string, a liquid eduction tube positioned in spaced relation within said tubular member and secured at the upper end thereof to said lastmentioned means, at least a portion of said eduction tube being composed 'of a porous material having a permeability between one and thirty darcies, and a pressure release valve positioned in the lower end of said eduction tube.

5. Means for transmission of liquids and the separation of gases in the production from a well comprising a coupling having a central low channel, a rigid, hollow cylindrical structure supported by said coupling `and having perforations such as to present negligible impedance to flow of said liquids and said gases, and a structure pendantly supported from said coupling within said cylindrical structure forming an exclusive path for flow of liquids in said well to said central flow channel comprising a cylinder of porous material, said material having a permeability between one and thirty darcies.

6. Means for transmission of liquids and the separation of gases in the production from a well comprising a coupling having a central ilow channel, a rigid, hollow cylindrical structure supported 'by said Icoupling and having perforations such as to present negligible impedance to flow of said liquids and said gases, and a structure pendantly supported from said coupling within said cylindrical structure forming an exclusive path for ow et liquids in said well to said central flow channel cornprising a cylinder of porous material, ysaid material having a permeability of between one and thirty darcies, and a pressure release valve secured in the lower end of said cylinder.

7. in a gas anchor the combination of a tubular member having a plurality of ports therein over substantially its entire length, means for connecting said tubular member to a producing string, a liquid eduction tube closed at its lower end positioned in spaced relation within said tubular member and `secured at the upper end thereof to said last mentioned means, at least a portion of said eduction tube being `composed of a porous material having a permeability between one and thirty darcies, and pressure release valve positioned in the lower end of said eduction tube.

References Cited in the le of this patent UNITED STATES PATENTS 1,329,171 Garry Jan. 27, 1920 1,749,216 Goldman Mar. 4, 1930 2,104,339 Arutunoff Jan. 4, 1938 2,111,758 Davis Mar. 22, 1938 2,234,977 Ohland Mar. 18, 1941 2,291,378 Courtney July 28, 1942 2,346,602 OBannon Apr. 11, 1944 2,439,468 Hopkins Apr. 13, 1948 2,506,790 Ihrig et al May 9, 1950 2,523,091 Bruce Sept. 19, 1950 2,525,897 Greene Oct. 17, 1950 2,528,448 Munk Oct. 31, 1950 2,665,644 Wells Jan. 12, 1954

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