Gas lift utilizing a liquefiable gas introduced into a well

Claim 2

A gas lift method for lifting a well fluid from a well comprising first and second well conduits leading to a downhole region of the well, the conduits being in communication with each other in a downhole region and the second well conduit being in communication with well fluid in the well, the method comprising feeding a liquid lifting medium under pressure into the first well conduit to maintain a liquid column of liquid lifting medium in the first well conduit to provide a significant liquid column pressure at the downhole region of the first well conduit for lifting medium to pass into the second well conduit, the composition of the liquid lifting medium being such in relation to the temperature prevailing in the first well conduit, that the lifting medium will be heated above its critical temperature in a downhole vaporization region of the first well conduit for the lifting medium to change into a gas phase below the liquid column in the first well conduit, and the lifting medium being miscible with the well fluid to mix with well fluid and cause vaporization for the lifting of well fluid in the second well conduit.

Claim 3

A method according to claim 1, in which the pressure in the downhole region of the first well conduit is controlled by controlling the effective length of the liquid column.

Claim 4

A method according to claim 2, in which the effective length of the liquid column is controlled by controlling the level at which the upper level of the liquid column is maintained.

Claim 5

A method according to claim 2 or claim 3, in which the effective length of the liquid column is controlled by controlling the level at which the lower level of the liquid column is maintained.

Claim 6

A method according to claim 1, claim 2 or claim 3, in which the pressure in the downhole region is controlled by controlling the introduction pressure at which the liquid lifting medium is introduced into the first well conduit for the introduction pressure to supplement the pressure provided by the liquid column.

Claim 7

A method according to claim 4, in which the level of the lower level is controlled by controlling the composition of the liquid lifting medium to provide a boiling temperature range such that the geothermal temperature in the well will cause the liquid lifting medium to be heated above its boiling temperature range at the required level in the first well conduit.

Claim 8

A method according to claim 4, in which the level of the lower level of the liquid column is controlled by controlling the composition of the working medium such that it will be heated above the critical temperature by the geothermal heat in the first conduit at the required level to thereby establish the lower level of the column.

Claim 9

A method according to claim 1, in which the lifting medium comprises a hydrocarbon medium.

Claim 10

A method according to claim 8, in which the lifting medium comprises a mixture of C 2 and higher hydrocarbons mixed in suitable proportions to provide a boiling temperature range for the lifting medium appropriate for pressure and temperature conditions prevailing in the well.

Claim 11

A method according to claim 1, in which the two well conduits are the annulus and tubing string of the well, and in which the first well conduit is separated from well fluid by a packer located therein.

Claim 12

A method according to claim 1, which comprises recovering well fluid and lifting medium produced in the second well conduit, separating the lifting medium from the well fluid, and condensing the lifting medium for re-use.

Claim 13

A gas lift method for lifting a well fluid from a well comprising first and second downhole zones, the downhole zones being in communication with each other in a downhole region and the second downhole zone being in communication with well fluid in the well, the method comprising: (a) introducing a liquid working medium under pressure into the first downhole zone, the working medium comprising a liquefied gas and being miscible with the well fluid; (b) maintaining a column of liquid working medium in the first downhole zone to provide a downhole pressure in the first downhole zone which is sufficient to cause working medium to flow from the first downhole zone into the second downhole zone to mix with well fluid and form a well fluid mixture; and (c) the working medium having a composition which is such in relation to the downhole zone that the working medium will be heated above its critical temperature in the first downhole zone for a gas phase working medium to be produced in the first downhole zone, and which has a composition such that when it is heated by downhole heat and mixes with the well fluid it forms a well fluid mixture which is capable of boiling at the downhole temperature and pressure in the second downhole zone for the well fluid mixture to lift from the well.

Claim 14

A gas lift method for lifting a well fluid from a well comprising first and second downhole zones, the downhole zones being in communication with each other in a downhole region and the second downhole zone being in communication with well fluid in the well, the method comprising: (a) introducing a liquid working medium under pressure into the first downhole zone, the working medium comprising a liquefied gas and being miscible with the well fluid; (b) maintaining a column of liquid working medium in the first downhole zone to provide a downhole pressure in the first downhole zone which is sufficient to cause working medium to flow from the first downhole zone into the second downhole zone to mix with well fluid and form a well fluid mixture; and (c) the working medium having a composition which is such in relation to the downhole zone that the working medium will be heated above its critical temperature in the first downhole zone for a gas phase working medium to be produced in the first downhole zone, and which has a composition such that when it is heated by downhole heat and mixes with the well fluid it forms a well fluid mixture which is capable of boiling at the downhole temperature and pressure in the second downhole zone for the well fluid mixture to lift from the well.

Claim 15

A method according to claim 12, in which the downhole pressure which is provided in the first downhole zone is controlled by controlling the effective length of the liquid column.

Claim 16

A method according to claim 13, in which the effective length of the liquid column is controlled by controlling the level at which the upper level of the liquid column is maintained.

Claim 17

A method according to claim 13 or claim 14, in which the effective length of the liquid column is controlled by controlling the level at which the lower level of the liquid column is maintained.

Claim 18

A method according to claim 12 or claim 13, in which the pressure in the downhole region is controlled by controlling the introduction pressure at which the liquid lifting medium is introduced into the first well conduit for the introduction pressure to supplement the pressure provided by the liquid column.

Claim 19

A method according to claim 15, in which the level of the lower level of the liquid column is controlled by controlling the composition of the working medium such that it has a boiling temperature range for the geothermal temperature in the well to heat the working medium above its boiling temperature range for boiling to commence in the first downhole zone at the required level and thereby establish the lower level of the liquid column.

Claim 20

A method according to claim 12, in which the working medium comprises a mixture of C 2 and higher hydrocarbons mixed in suitable proportions to provide a boiling temperature range for the lifting medium appropriate for pressure and temperature conditions prevailing in the well.

Claim 21

A method according to claim 12, in which the first and second downhole zones are provided by the annulus and tubing string of the well respectively, and in which the annulus is separated from well fluid below it by means of a packer.

Claim 22

A method according to claim 12, which comprises recovering the well fluid and working medium produced from the well, and liquefying the working medium for re-use.