Completing wells in deep reservoirs containing fluids that are hot and corrosive

Claim 2

A well completing process which comprises: drilling a borehole into a relatively deep, hot, highly pressurized subterranean reservoir which contains fluid which, at the reservoir conditions, is corrosive to low alloy steel; installing in the borehole a casing string assembly in which the bottom portion has a corrosion resistant composition capable of resisting corrosion by the reservoir fluid at the reservoir conditions, with said bottom portion being at least about 20 feet long and being arranged to extend substantially into or through the reservoir interval; equipping the borehole with wellhead components inclusive of a tubing string hanger capable of suspending and sealing around a tubing string extending within the casing string; suspending a tubing string having a composition capable of resisting corrosion by the reservoir fluid at the reservoir conditions from the tubing hanger so that the tubing string extends into the corrosion resistant portion of the casing string; establishing at least one path of fluid communication between the reservoir and the interiors of the tubing and casing strings; circulating fluids within the tubing and casing strings to the extent required to establish a hydrostatic pressure within the bore-hole, at depth of the reservoir, which is less than the fluid pressure within the reservoir; producing fluid from the reservoir by allowing an outflow of fluid through the top of the tubing string while injecting fluid into the top of the casing string-tubing string annulus at a rate and pressure sufficient to confine substantially all of the reservoir fluid that enters the borehole within the tubing string and the corrosion resistant portion of the casing string; and as reservoir fluid flows up through the tubing string to a point beyond the tubing hanger, mixing substantially each portion reaching that location with a corrosion inhibitor effective for substantially preventing its corroding of a low alloy steel.

Claim 3

The process of claim 1 in which: a corrosion resistant upward facing conical sealing ledge is connected into the corrosion resistant portion of the casing string; a corrosion resistant downward facing conical sealing ledge adapted to mate with the ledge in the casing string is connected into the tubing string; and the length of the tubing string is arranged so that, when the average temperature of the tubing string is near that of the formations overlying the reservoir, the sealing ledges are separated, but when the average temperature of the tubing string is near the reservoir temperature the expansion of the tubing string engages the sealing ledges and holds them in substantially fluid-tight engagement.

Claim 4

The process of claim 2 in which: the downhole sealing ledges are subsequently disengaged by terminating the upflow of reservoir fluid and allowing the average temperature of the tubing string to decrease; and fluid is circulating within the tubing and/or casing string to the extent required to position a selected fluid within the borehole at the depth of the reservoir.

Claim 5

The process of claim 1 in which all of the reservoir fluid-contacted surfaces of the corrosion resistant tubing string and bottom portion of the casing string are composed of highly alloyed, super austinitic strength steels having yield strengths in the range of 150 to 250 KSI.

Claim 6

The process of claim 4 in which substantially all of the remaining portions of the tubing and casing string assemblies are composed of low alloy steels having strength and corrosion resistance properties at least substantially equivalent to those of an AISI 4130-4146 steel in the 75-135 KSI minimum yield category.

Claim 7

A well completing and operating process which comprises: drilling a borehole into a relatively deep, hot, highly pressurized subterranean reservoir which contains fluid which at reservoir conditions is corrosive to low alloy-steel; installing in the borehole a casing string assembly in which the bottom portion has a corrosion resistant composition capable of resisting corrosion by the reservoir fluid at reservoir conditions, with said bottom portion being at least about 20 feet long and being arranged to extend substantially into or through the reservoir interval; equipping the borehole with wellhead components inclusive of a tubing string hanger capable of suspending and sealing around a tubing string extending within the casing string; suspending a tubing string having a composition capable of resisting corrosion by the reservoir fluid at reservoir conditions from the tubing hanger so that the tubing string extends into the corrosion resistant portion of the casing string; establishing at least one path of fluid communication between the reservoir and the interiors of the tubing and casing strings; circulating fluids within the tubing and casing strings to the extent required to establish a hydrostatic pressure within the borehole at depth of the reservoir which is less than the fluid pressure within the reservoir; producing fluid from the reservoir by allowing an outflow of fluid through the top of the tubing string while injecting fluid into the top of the casing string-tubing string annulus at a rate and pressure sufficient to confine substantially all of the reservoir fluid that enters the borehole within the tubing string and the corrosion resistant portion of the casing string; as reservoir fluid flows up through the tubing string to a point beyond the tubing hanger, mixing substantially each portion reaching that location with a corrosion inhibitor effective for substantially preventing its corroding of a low alloy steel; and subsequently circulating fluids within the tubing and casing strings to the extent required to establish a hydrostatic pressure within the tubing and casing strings which is more than the fluid pressure within the reservoir.

Claim 8

A well completing and operating process which comprises: drilling a borehole into a relatively deep, hot, highly pressurized subterranean reservoir which contains fluid which at reservoir conditions is corrosive to low alloy-steel; installing in the borehole a casing string assembly in which the bottom portion has a corrosion resistant composition capable of resisting corrosion by the reservoir fluid at reservoir conditions, with said bottom portion being at least about 20 feet long and being arranged to extend substantially into or through the reservoir interval; equipping the borehole with wellhead components inclusive of a tubing string hanger capable of suspending and sealing around a tubing string extending within the casing string; suspending a tubing string having a composition capable of resisting corrosion by the reservoir fluid at reservoir conditions from the tubing hanger so that the tubing string extends into the corrosion resistant portion of the casing string; establishing at least one path of fluid communication between the reservoir and the interiors of the tubing and casing strings; circulating fluids within the tubing and casing strings to the extent required to establish a hydrostatic pressure within the borehole at depth of the reservoir which is less than the fluid pressure within the reservoir; producing fluid from the reservoir by allowing an outflow of fluid through the top of the tubing string while injecting fluid into the top of the casing string-tubing string annulus at a rate and pressure sufficient to confine substantially all of the reservoir fluid that enters the borehole within the tubing string and the corrosion resistant portion of the casing string; as reservoir fluid flows up through the tubing string to a point beyond the tubing hanger, mixing substantially each portion reaching that location with a corrosion inhibitor effective for substantially preventing its corroding of a low alloy steel; and subsequently circulating fluids within the tubing and casing strings to the extent required to establish a hydrostatic pressure within the tubing and casing strings which is more than the fluid pressure within the reservoir.

Claim 9

The process of claim 6 in which: a corrosion resistant upward facing conical sealing ledge is connected into the corrosion resistant portion of the casing string; a corrosion resistant downward facing conical sealing ledge is connected into the corrosion resistant portion of the casing string; a corrosion resistant downward facing conical sealing ledge adapted to mate with the ledge in the casing string is connected into the tubing string; and the length of the tubing string is arranged so that when the average temperature of the tubing string is near that of the formations overlying the reservoir the sealing ledges are separated, but when the average temperature of the tubing string is near the reservoir temperature the expansion of the tubing string engages the sealing ledges and holds them in substantially fluid-tight engagement.

Claim 10

The process of claim 6 in which: the downhole sealing ledges are subsequently disengaged by terminating the upflow of reservoir fluid and allowing the average temperature of the tubing string to decrease; and fluid is circulating within the tubing and/or casing string to the extent required to position a selected fluid within the borehole at the depth of the reservoir.

Claim 11

The process of claim 6 in which all of the reservoir fluid-contacted surfaces of the corrosion resistant tubing string and bottom portion of the casing string are composed of highly alloyed, super austinitic strength steels having yield strengths in the range of 150 to 250 KSI.

Claim 12

The process of claim 9 in which substantially all of the remaining portions of the tubing and casing string assemblies are composed of low alloy steels having strength and corrosion resistance properties at least substantially equivalent to those of an AISI 4130-4146 steel in the 75-135 KSI minimum yield category.