US2262490A - Casing head structure - Google Patents

Description

1941- w. sf. M. E. CRAKE 2,252,490 7 I CASING STRUCTURE Filed Nov. 12, 1940 5 52 FiQ m invznior: Witfrzd St Maur Eimorz (rake Fig. I

Patented Nov. 1 ,1, 1 941 5; 'EPATENT orrlce casino new s'rnuorunr.

Wilfred St. Maur Elmore Crake, Houston, Tex assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application November 12, 1940, Scrial- No. 365,252 '1 Claims. (oi. 166 -14)" The present invention relates to oil and gas well casing heads and tubing supports and pertains more particularly to a device of the expansion joint type adapted tomaintain the load or stress on the elements supporting a casing string at an approximately constant value by compensating for the expansion or contraction of said casing string due to temperature variations within the oil well. m

In deep wells, casing strings are set under certain temperature conditions with the lower-end imbedded and held in cement and with the upper end held by the casing head. Since the ends of the casing string are thus rigidly fixed, a

different set of temperature conditions causes the casing string to be stretched or compressed by various amounts. Particularly in deep wells,

1 a change in temperature of the casing string which may be due to variations of the temperature of the fluid flowing therethrough, and which may sometimes have amplitudes as high as 100 F., often causes failure of the string and results in highly expensive corrective measures and replacements or even in a total loss of the well.

It is therefor an object of this invention to provide means for, supporting casing strings wherein the point-of support is not rigidly fixed at the casing head,'but is capable of a limited axial motion whenever such motion is made necessary by a temperature-responsive elongation or contraction of the casing string.

It is also an object of the present invention to.

provide a device for maintaininga constant load on the casing head by compensating for varia tions in the length of a casing string caused by temperature variations.

It is a further object of this invention to provide a system wherein a compensation in the length of casing string is automatically effected in response to any changes in the length of said string caused by well conditions.

With the above and other objects in view the invention has particular relation to certain novel features of construction,,operation, and arrangement of parts, an example of which is given in this specification and illustrated in the accom panying drawing, wherein:

Figure I is a partial vertical sectional view of a preferred embodiment of the present invention.

Figure 11 is a transverse sectional view taken along the lines II-II of Figure I.

Figure 111 is a schematic view of the present casing support and a preferred control system as installed at a. well.

Referring to Figures 1 and II of the drawing, the present device comprises a casing head generally indicated at-i. Any number of such casing heads may be used if desired to suspend a plurality of casing strings. For purposes of illustration, however, a casing string 20, is shown directly suspended on casing head I and a casing string 2bis shown suspended indirectly on casing head I by means of'a tapered coupling 4. The last or so.-ca11ed "oil string 3 is suspended as subsequently described on the casing supporting device of the present invention. For this purpose a special casing head spool 5 is attached by means of flanges above the casing head I and is added to the assembly, in the illustration shown, after the intermediate or penultimate string 2b has been set. This special spool 5 has a flange 6 in its lower portion, preferably a large flange I in its upper portion, and vertical radial braces 8 between said flanges 6 and 1. Above and fastened to the upper large flange l is a packing ring l0 carrying a packing gland H and packing retainer ring l2. This packing assembly or any other suitable packer means is adapted to effect a seal about the last casing string 3 which extends therethrough, and to prevent the escape of fluid from the annular space between the intermediate casing string 2b and the last casing string 3.

The oil string 3 is suspended in any suitable manner, such as by means of a tapered bowl 2!! and tapered grips 2|, in a transverse head 22, which is supported by rams 23. The rams 2,3 fit slidingly in cylinders 24, which are supported and project up from the large flange l on the special spool 5. conduits 53, are provided in the lower portion of the cylinders for injecting fluid thereinto from the subsequently described control system. In a preferred embodiment, as shown in Figure 2, three hydraulic cylinders 24 and rams or pistons 23 are provided and vertical radial braces 8 forthe spool flange are positioned with their outer ends directly under said cylinders. Likewise, attached to the upper surface of the flange l and spaced in between said cylinders 24 are combination guiding and motion-limiting rods 25, which project through the head 22 and are .fltted with limiting stops in the form of shoulders 26 below said head and nuts 2 l above said head.

Above the head 22 is a tubing head 30, which supports the tubing 3| and closes the annular space between the tubing 3| and oil string 3.

Means,.such as ports 28 and The tubing head is surmounted by a suitable valve assembly or Christmas tree" 32, as shown in Figures I and III. I

Pressure fluid is injected through ports 28 into the cylinders 24 to raise the rams 23 and is withdrawn therefrom to lower the rams 23 in response to increases and decreases, respectively, in the length of the casing supported by the floating well head. The amount and the pressure of fluid in the supporting cylinders 24 may be regulated either manually, for example, in accordance with the readings of suitable temperature and pressure indicating devices, or by means of asuitable control system, such as described hereinbelow.

The control system comprises broadly any suitable means for regulating the amount of fluid in the cylinders 24, in response to changes in the load imposed on the suspending assembly as a result of variations casing.

In a preferred embodiment pressure fluid is obtained from the annular space 33, as shown in Figure I, between the casing'3 and tubing 3| and is led from a port 34 in the tubing head 30 through conduit 40, preferably to a suitable regulating valve such as a diaphragm motor valve 4|. The diaphragm 42 of motor valve 4| is preferably exposed by means of line 45 to the fluctuating presbe accurately controlled. A gauge 69 connected to the impeller side of the pump is provided to aid in setting the control valve 4|. Pump 50, having a suction line 5| depending into a sump or reservoir 52, forces pressure fluid, such as oil, water, etc., through a line 53 leading to the cylinders 24. Line 53 contains a safety or regulating valve 54, for example, of the spring-loaded type, a check valve 55, and a line cross 56. The safety valve 54 is provided to control the maximum pressure applied to the cylinders by means of the pump action and may be provided with a return line 60, discharging back into the sump 52.

of the temperature of the oil, from the sump or reservoir 52 through the line 53 into the ram system.

By means of the regulating valve 54 in line 53 and the bleeder valve 59 and line 58, which valves are set for a predetermined pressure, the pump 50 maintains a constant upward force on the rams 23 and will pump fluid into the cylinders 24 as long as the ram-supported casing 3 continues I to extend in length. Pressure developed by the pump in excessof this pressure-is discharged by safety valve 54 through line back into the sump 52. The upward limit of movementof the rams is governed by the stop nuts 12 on the upper end ofthe increased weight applied to the fluid in the The check valve 55 prevents any pressure, in excess of that for which valve 54 is set, from flowing back through valve 54 and the pump 50. To one side of cross 55 a pressure gauge or, preferably for accuracy, a pair of pressure gauges 51 are connected and to the other side of said cross 58 is attached a bleeder line 58 discharging to the sump 52 and containing a bleeder or relief valve 59 set to release from cylinders 24 and line 53 any pressure in excess of a predetermined value.

-In operation of the present device the well head structure is assembled as described above. In the preferred embodiment the pressure fluid which provides the motive power for the pump 50 is obtained from the annular space 33 between the casing and tubing, as shown in Figure 1. However, any other source of pressure fluid or other types of prime mover units which can be easily regulated may be used, if desired, the important object being mainly to effect an axial displacement of thepointof support of the casing as a function of an elongation or contraction oi the casing string. In the preferred form, as shown, the application of pressure fluid to the pump 50 is controlled by the diaphragm motor cylinders 24 will cause the bleeder valve 59 to open and discharge through the line 58 into the sump or reservoir 52. The bleeder valve 59 is set to relieve at a slightly higher pressure than the inlet regulating valve 54. The pressure gauges 51 are used in setting the valves 54 and 59 to a previously determined calculated value which is designated as m and may be calculated by the W is the portion of the weight of the casing which it is desired to support at the casing head (usually as determined by field practice requirements from to of the casing weight) plus the weight of the tubing string, floating casing head assembly, rams, etc.;

A is the internal area ofoil string 3;

A1 is the internal area of tubing 3|;

A2 is the external area of tubing 3|;

A: is the areaof the rams 23:

p is the pressure inside the oil string 3;

171 is the pressure inside the tubing 3| and p: is the pressure required in cylinders 24 to balance the load W.

Friction, since it will be negligible in comparison with other forces involved, is neglected in the above formula. It may be readily seen that W represents the force acting downward and the force acting upward is the expression within the brackets, which expression may be readily revised to suit different conditions, such as for example when more than one casing string is supported by the floating head.

Since A, A1, A2 and A3 are constants for any specific assembly and p and 121 do not normally vary rapidly, p2 may be calculated for any set of conditions of the upward forces. Further, since 291A: is usually small compared with W, while the well is flowing, a suitable constant may be substituted by assuming :01 at a maximum value,

which would be the tubing shut-in" pressure.

ing tubular members rigidly connected together and having its lower end held stationary, hy-

s'ubstantially constant portion of the weight of I inner casing strings, a stationary casing head member supporting an outer casing string, a second casing head member movably carried by said stationary member, engaging means on said ,second member for supporting an inner casing string said inner casing string comprising tubular members rigidly connected together and having its lower end held stationary, and pressure means slidable in a direction co-axial with the casing strings for supporting said movable member on said stationary member.

2. in a well head structure for-supporting a substantially constant portion of the weight of inner casing 1 strings, a stationary casing head member supporting at least one outer casing string, a plurality of vertical hydraulic cylinders mounted on said member, rams adapted for reciprocation in said cylinders, said rams extending vertically upwards from said cylinders, a crossheadcarried by said rams, engaging means on said cross head for supporting at least one inner casing string said inner casing string comprising tubular members rigidly connected together and having its lower end held stationary, and hy-v draulic means in communication with said cylinders for applying fluid pressure to said-rarns.

3. In a well head structure for supporting a substantially constant portion of the weight of inner casing strings, a stationary casing head member supporting at least. one outer casing string, a plurality of vertical hydraulic cylinders mounted on said member, rams adapted for reciproc'ation in said cylinders, said rams extending vertically upwards from said cylinders, a crosshead carried by said rams, engaging means on said crosshead for supporting at least one inner casing string said inner casing string comprising tubular members rigidly connected to ether and having its lower end held stationary, vertical guide means mounted on said casing head member' slidingly engaging said crosshead. stop means on said guide means for limiting the verticalv travel of said crosshead, and hydraulic means in communication with said cylinders for applying fluid pressure to said'rams,

4. In a wellhead structure for supporting a substantially constant'portion ofthe weight of inner casing strings, a stationary casing'head member supporting at least one outer casing.

draulic means in communication with said cylinders for apply fluid pressure .to said rams, and

. valve means for maintaining said pressure at a substantially constant value, said valve means comprising a regulating valve adapted to maintain the pressure applied from said hydraulic means to said cylinders at a predeterminedvalue,

and a safety valve adapted to release from said cylinders pressures in excess or said predeter-, mined value.

5. In a well head structure for supporting a substantially constant portion of the weight of inner casing strings, a stationary casing head member supporting at least one outercasing string, a-plurality of vertical hydraulic cylinders mounted on said member, rams adapted for reciprocation in saidcylinders, said rams extending vertically upwards from said cylinders, a crosshead carried by said rams, engaging means on said crosshead for supporting at least one inner casing string said inner casing string comp'ris ing tubular members rigidly connected together and having its lower and held stationary, hy-- draulic means incommunication with said cylin-- ders'ror applying fluid pressure to said rams, and

valve means adapted to regulate the amount of pressure fluid in said cylinders in response to changes in the length of the casing strings supported by said crosshead.

6. In a well head structure for supporting a substantially'constant portion of the weight of inner casing strings, a stationary casing head member supporting at least one outer casin string, a plurality of vertical hydraulic cylinders I mounted on said member, rams adapted for reciprocation in said cylinders; said rams extending vertically upwards from said cylinders, a crosshead carried by said rams, engaging means on said crosshead for supporting at least one inner casing string said inner casing string comprising tubular members rigidly connected together ,and having its lower end held stationary, hydraulic means. in communication with said cylinders for applying fluid pressure to said rams.

and valve means adapted to regulate the amount or pressure fluid in said cylinders in response to changes in the pressure in said cylinders.

'l. A producing well structure comprising outer and inner rigid casing strings depending into a well borehole, said strings having their lower ends rigidly held in the borehole, in combination with a well head structurecomprising a stationstring, a plurality of vermin hydraulic cylinders mounted on said member, rams adapted for reciprocation in said cylinders, said rams extending vertically upwards from said-cylinders, a crosssaid crosshead for supporting at least one inner casing string said inner casing string compris head carried by said rams, engaging means on ary casing head'member supporting said outer casing string, a second casing head member mov-. ably carried by said stationary member, means on said second member for engaging said inner casing string, and pressure means slidable .in a direction coaxial with the casing strings for supporting said movable member and a substantially constant portion of the weight or said inner casing string engaged by said movable member on said stationary member.

WIIIBED ST. MAUR ELMORE CRAKE.

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