Abstract:
A well drilled with air or gas as a circulating medium traversing pay zones with greater than normal pressures or pressures such that hydrocarbons would permeate drilling fluids and cement is drilled and completed while permitting a continuous flow of hydrocarbons from the well until it is desired to shut the well in at the surface. The intermediate casing string and the production casing string cooperate with the tubing so that the cement for the production string may be positioned without contact with the hydrocarbons.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the drilling and completion of oil and gas (more particularly gas) wells with greater than normal pressures preventing conventional &#34;open hole&#34; completions--or for completion of air or gas drilled wells where damage to the producing formation may occur by using various fluids or cement to kill the flow of hydrocarbons. 
     BACKGROUND OF THE INVENTION 
     The more recent oil and gas explorations have resulted in finding of such formations at depths and pressures that are substantially greater than those encountered in previous years. The conventional techniques for drilling and completing a well, such as a gas well, at depths where pressures are greater than the hydrostatic pressure of normally weighted drilling fluids are not suitable. At these depths the pressures of the gas are such that the gas permeates the cement during completion of the well deactivating its setting chemistry. Various attempts at completing wells, such as gas wells, at these depths and pressures have been prohibitively expensive and sometimes have resulted in failure. When the hydrostatic pressure of the drilling fluid is raised to the point where it does not allow the entry of hydrocarbons, the fluid is generally forced into the porosity of the pay zones sometimes destroying their ability to produce. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention relates to method and apparatus particularly suited for completing wells, such as gas wells, at depths such that the pressure exceeds the burst strength of conventional external casing packers. During the completing procedures, gas is allowed to flow from the well at all times unitl it is desired to shut the well in. 
     In a preferred embodiment of the invention, a well is conventionally drilled to a depth of about 11,500 feet and 95/8 inch casing is placed. The well is drilled with an 81/2 inch bit using air as a circulating medium until commercial quantities of gas are encountered. During the drilling, gas will be flowing out of the well through the 95/8 inch casing, being diverted through a conventional blooie line and being burned as it exits at distances of 200 feet or greater from the drilling operations. 51/2 inch casing is run in the hole with the bottom portion sealed, such as the first two joints being filled with cement. The 51/2 inch casing is provided with external casing packers and is positioned so that when the end of the 51/2 inch casing is below the pay zone, the external packers will be in a desired position above the pay zone. The 51/2 inch casing is provided with cementing ports located above the external packers. The slips for the 51/2 inch casing are seated in the 135/8 inch casinghead to ensure that the gas is passing through two 4 inch outlets in the casinghead below the slips. A 27/8 inch tubing string is then run down the 51/2 inch casing with a Vannysystem perforating gun at its lower end. A tubing packer is located on the tubing string at a location below the external packers of the 51/2 inch casing. 
     In operation, the main rig is moved away after the 51/2 inch casing has been run and a completion rig is moved into position. The 27/8 inch tubing string is run in the 51/2 inch casing to a desired location and then the tubing packer is activated to provide a seal between the external surface of the 27/8 inch tubing and the internal surface of the 51/2 inch casing. A christmas tree is installed and the perforating gun is fired to perforate the 51/2 inch casing below both external casing packers so that gas will flow through the perforated 51/2 inch pipe and then, because of the seal between the 27/8 inch tubing and the 51/2 inch casing, the gas flows out of the well through the 27/8 inch tubing and the annulus between the 95/8 inch--51/2 inch casings. Hydrostatic pressure is then established in the annular space between the 27/8 inch tubing and the 51/2 inch casing to expand the external casing packers to provide a seal between the upper and lower formations penetrated by the 81/2 inch drill hole. The hydrostatic pressure is increased to open the cementing ports above the external casing packers. Water is pumped down the 95/8 inch--51/2 inch annulus, through the cementing ports and up the 51/2 inch--27/8 inch tubing annulus until the water column is balanced at the surface. The water is followed by a predetermined amount of cement until the bottom of the cement is about 100 feet above the ports. In a preferred embodiment, the 27/8 inch tubing has a smooth external surface even at the joints so that a cementing sealing plug may be positioned between the water and the cement. Gas continues to flow through the 27/8 inch tubing until the cement hardens, at which time the well is shut in. 
     It is an object of this invention to provide method and apparatus for the completion of wells at depths such that the bottom hole pressures exceed the burst strength of existing external casing packers. 
     It is another object of this invention to provide method and apparatus for the cementing of a well having high pressures so that the gas will not permeate the cement. 
     It is a further object of this invention to provide method and apparatus for the completion of such a well by providing for the controlled flow of gas out of the well at all times until it is desired to shut in the well. 
     Other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which like reference characters refer to the same parts through the various views. The drawings are approximately to scale, illustrating principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a view partially in section of some of the components in the upper portion of a conventional well; 
     FIG. 2 is a view partially in section illustrating components located above those in FIG. 1; 
     FIG. 3 is a view partially in section at a lower portion of the well; 
     FIG. 4 is a view partially in section of some of the components at the bottom of the well; 
     FIG. 5 is a view illustrating a completion rig in place; and 
     FIG. 6 is a view partially in section of the cement in place. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Some of the components in the upper portion of a well are illustrated in FIG. 1. The casing head 2 of the 20 inch casing 4 is fixed in position such as being cemented in a 24 inch hole. The slips 6 for the 133/8 inch casing 8 are set in the casing head 2; the slips 10 for the 95/8 inch casing 12 are set in the casing head 14 of the casing 12; and the slips 16 of the 51/2 inch casing 18 are set in the casing head 20 of the casing 12. Bleed lines 22 divert gas from the 95/8 inch casing 12 to a blooie line. The blooie line is connected to a pit located about 200 feet or more from the rig and the gas is burned as it exits into the pit (not shown). In the preferred embodiment of the invention to be described below, the 95/8 inch casing 12 has been installed to a depth of about 11,500 feet and the 51/2 inch casing has not been installed. 
     As illustrated in FIG. 2, on top of the casing head 20, there are two ram type blow out preventers 26 and 28 and above them an annular type blow out preventer 30. Above the preventer 30, there is located the slip insertion spool 32, for a purpose to be described below. The rotating head 34 is above the insertion spool 32 and an exit 36 connected to a blooie line. 
     Suitable apparatus (not shown) is moved through and out of the 95/8 casing 12 and an 81/2 inch hole 38 is drilled below the 95/8 inch casing 12. The drilling of the hole is continued until the pay zone is reached and the desired commercial flow of gas is coming up between the drill bit and the 95/8 inch casing 12, such as a flow rate of 20 MMCFGD. At this time, the drilling is stopped and the drilling apparatus withdrawn from the well. 
     The next operation is to strip a 51/2 inch casing 18 into the well through the rotating head 34. The lower portion 38a of the 51/2 inch casing 18 is sealed, such as by filling the first two joints with cement. An external casing packer 40 is located at a predetermined position on the outer surface of the 51/2 inch casing 18. Although only one external casing packer 40 is illustrated, it is to be understood that a plurality of external casing packers may be used. The external casing packer 40 is located a predetermined distance above the pay zone. The external casing packer 40 illustrated in FIG. 2 comprises an expandable sleeve 42 the ends 44 of which are firmly sealed to the outer surface of the 51/2 inch casing 18. A plurality of holes 46 are made in the 51/2 inch casing 18 between the ends 44 of the sleeve 42 through which the fluid used to expand the sleeve 42 will pass. The 51/2 inch casing 18 is provided with a plurality of cementing ports 48 filled with a suitable material 50 capable of being blown out at suitable pressures, as described below. 
     As the 51/2 inch casing 18 is being stripped into the hole through rotating head 34, gas is flowing out of the exit 36 to a blooie line and out of the bleed line 22 to the blooie line. When the predetermined amount of 51/2 inch casing 18 has been stripped into the hole, the rubbers in the annular blow out preventer 30 are inflated so that the gas flow is only through the blooie line. The rotating head is lifted so that the slip insertion spool 32 is accessible. The slip insertion spool 32 is opened and the slips 16 are attached to the 51/2 inch casing 18. The slip insertion spool 32 is reassembled and the rotating head moved back into position and the rubbers of the annular blow preventer 30 are deflated so that some gas is again flowing out of exit 36. The 51/2 inch casing 18 is lowered until the slips are seated in the casing head 20 so that the gas from the drill hole 38 is flowing through the annular space between the outer surface of the 51/2  inch casing 18 and the inner surface of the 95/8 inch casing 12 and out through bleed line 22 to the blooie line. The use of the slip insertion spool is the preferred embodiment of the invention. However, under some conditions, the slips 16 of the 51/2 inch casing 18 can be attached and then moved through the rubbers in the rotating head. 
     The ram type blow preventers 26 and 28, the annular type blow preventer 30, the slip insertion spool 32 and the rotating head are removed and the completion rig is moved into position. The 27/8 inch tubing 54 is run in with apparatus, as described below, and including the christmas tree 52, illustrated in FIG. 5, is positioned on the casing head 20. The 51/2 inch casing 18 is cut prior to the positioning of the christmas tree 52. A perforating gun 56 is secured to the lower end 18 of the 27/8 inch tubing. An external packer 58 is secured to the outer surface of the 27/8 inch tubing 54 at a predetermined location so that the external packer 58 is located below the external packer 40 secured to the outer surface of the 51/2 inch casing 18. The external packer 58 can be of any conventional design. A perforated collar 60 is secured to the 27/8 inch tubing between the external packer 58 and the perforating gun 56 to provide a passageway for the gas from the pay zone into the 27/8 inch tubing after the perforating gun has been discharged. After all of the 27/8 inch tubing 54 has been installed, the external packer 58 is expanded so as to provide a seal between the outer surface of the 27/8 inch tubing 54 and the inner surface of the 51/2 inch casing 18. Although only one external packer 58 is illustrated, it is to be understood that a plurality of external packers 58 may be utilized. The apparatus is now in position so that the well may be completed as described below. 
     A suitable detonator (not shown) is dropped down the 27/8 inch tubing 54 to discharge the perforating gun 56 to make openings in the 51/2 inch casing 18. Gas from the pay zone moves through the openings formed by the blast from the perforating gun. Since the external packer 58 has formed a seal between the 27/8 inch tubing 54 and the 51/2 inch casing 18, as described above, the only exit for the gas entering into the 51/2 inch casing 18 is through the 27/8 inch tubing 54. Gas is also continuing to flow upwardly in the annulus between the 51/2 inch and 95/8 inch casings. Valves 62 control the flow of gas through the 27/8 inch tubing. 
     Water (KCl) is now fed through valve 64 into the annulus between the 27/8 inch tubing 54 and the 51/2 inch casing 18. The external packer 58 will limit the movement of the water so that hydrostatic pressure will start building. When the hydrostatic pressure has reached a predetermined amount, such as about 4000 psi, the external packer sleeve 42 will start to expand and will continue to expand until it is in sealing engagement with the wall 66 of the 81/2 inch hole 38. Additional water is added until the hydrostatic pressure reaches a predetermined amount, such as about 4500 psi, at which pressure, the material 50 is blown out of the cement ports 48. Water is continued to be added and flows out through the ports 48 and then upwardly in the annulus between the 51/2 inch casing 18 and the 95/8 inch casing 12. The addition of the water is continued until the well is full of water. 
     Cement is introduced into the annulus between the 51/2 inch casing 18 and the 95/8 inch casing 12. A predetermined amount of cement is introduced and is moved down the annulus until the bottom of the cement is at a desired point above the cement ports 48. The location of the bottom of the cement may be readily determined by knowing the amount of water displaced out of the annulus between the 27/8 inch tubing 54 and the 51/2 inch casing 18. During all these operations, gas continues to flow through the 27/8 inch tubing 54. The cement is allowed to set until it has reached a predetermined hardness. The foregoing procedures allow the cement to be introduced and set with no contact between the cement and the deleterious gases at the high pressures prevailing in the well. After the cement has set, the flow of gas through the 27/8 inch tubing 54 is stopped by shutting in the well. 
     In another embodiment, the 27/8 inch tubing 54 is provided with internal joints so that its complete external surface is smooth. A cement sealing plug 68 is positioned in the annulus between and in contact with the 27/8 inch tubing 54 and the 51/2 inch casing 18. Cement 70 is then introduced and forces the cement sealing plug to move downwardly. When the desired amount of cement has been introduced, another cement sealing plug 72 is installed and water or other means is used to force the cement sealing plugs 68 and 72 and the cement 70 to move downwardly until they are in the desired location. 
     It is to be understood that dimensions of the various components may be chosen for different types of wells. 
     While the preferred embodiments of the invention have been illustrated and described herein, it may be otherwise embodied and practiced within the scope of the following claims.