Downhole gas separation method and system

A method of separating a multi-component fluid in a wellbore in fluid communication with one or more subterranean, fluid-producing zones and one or more disposal zones, comprising the steps of:

• (a) incorporating in the wellbore at least one fluid separation membrane having a feed side in contact with the membrane at a feed pressure and a permeate side at a permeate pressure, said membrane having a retentate stream being withdrawn from the feed side and a permeate stream being withdrawn from the permeate side;
• (b) passing the multi-component fluid from the producing zone to the feed side of the membrane;
• (c) separately removing the permeate stream and the retentate stream from contact with the membrane;
• (d) determining the pressure of the multi-component fluid on the feed side of the membrane and the pressure of the permeate on the permeate side of the membrane;
• (e) determining a pressure differential across the membrane;
• (f) if the pressure differential is less than a desired value, decreasing the pressure of the permeate on permeate side of the membrane;
• and
• (g) injecting the permeate into one or more disposal zones.

A method of separating a multi-component fluid in a wellbore in fluid communication with a subterranean, fluid-producing zone and a disposal zone, comprising the steps of:

• (a) providing in the wellbore a membrane having a feed side and a permeate side and being selective for one or more components of the multi-component fluid;
• (b) passing the multi-component fluid from the producing zone across the feed side at a feed pressure;
• (c) maintaining a pressure on the permeate side of the membrane lower than the pressure on the feed side of the membrane, thereby yielding a permeate containing increased quantity of the more permeable fluid and decreased quantity of the less permeable fluid and a retentate containing decreased quantity of the more permeable fluid and increased quantity of the less permeable fluid components;
• (d) recovering a retentate stream;
• and
• (e) disposing of the permeate by injecting it into the disposal zone.

A method of disposing of at least one component of a multi-component fluid mixture produced into a fluid-containing subterranean formation penetrated by a wellbore, comprising the steps of:

• (a) separating in the wellbore the multi-component fluid into a first stream rich in at least one component and a second stream depleted of the at least one component, said first and second streams being separated from each other;
• (b) directing to the earth's surface the second stream;
• (c) injecting into the wellbore a third stream comprising and co-mingling the first stream and third stream in the wellbore to produce a co-mingled stream, the hydrostatic head of the third stream providing compression of the co-mingled stream;
• and
• (d) injecting the co-mingled stream into a subterranean disposal zone penetrated by the wellbore.

A method of separating a multi-component gas in a wellbore in fluid communication with a subterranean, gas-bearing formation, comprising the steps of:

• (a) incorporating in the wellbore a gas separation membrane to provide a permeate gas enriched in more readily permeable gas components and a non-permeate gas depleted of the more readily permeable gas components;
• (b) subjecting the gas separation membrane to the multi-component gas;
• (c) withdrawing the non-permeate gas from one side of the membrane and withdrawing permeate gas from the other side of the membrane;
• (d) maintaining the pressure of the permeate on the permeate side of the membrane at a pressure below the feed pressure;
• and
• (e) placing the permeate stream into the disposal zone.

A method of separating a multi-component fluid in a wellbore in fluid communication with a subterranean, fluid-producing zone and a subterranean disposal zone, comprising the steps of:

• (a) incorporating in the wellbore one or more fluid separation membranes having a feed side and a permeate side;
• (b) passing across the membrane on the feed side at a feed side pressure a flowing stream of the multi-component fluid obtained from the producing zone;
• (c) withdrawing from the feed side a retentate stream depleted in at least one component compared to the multi-component fluid;
• (d) withdrawing from the permeate side a permeate stream at a permeate pressure, said permeate stream being enriched in at least one component compared with the multi-component fluid;
• (e) regulating the pressure of the permeate on the permeate side of the membrane at a pressure below the feed pressure;
• (f) passing the retentate stream to a treatment unit outside the wellbore;
• (g) in the treatment unit, separating from the retentate stream one or more non-hydrocarbon components;
• (h) pressurizing the one or more non-hydrocarbon components to a higher pressure;
• (i) co-mingling the pressured non-hydrocarbon components with a pressurized aqueous liquid and introducing the co-mingled mixture into the wellbore;
• (j) passing the co-mingled mixture down the wellbore and across the permeate side of the membrane, thereby causing the permeate to co-mingle with the co-mingle mixture flowing across the permeate side;
• and
• (k) placing the mixture resulting from step (j) into the disposal zone.

A fluid separation system for installation within a wellbore in fluid communication with a subterranean formation containing a multi-component gas, comprising:

• (a) a membrane separator having a feed side and a permeate side, said membrane separating one or more permeable gas components from one or more less permeable gas components;
• (c) a pressurizing means in the wellbore for receiving permeate gas from the separation membrane and pressurizing the permeate gas to a higher pressure;
• (d) means for conveying the multi-component gas to the feed side of the membrane separator;
• (e) means for conveying the non-permeate gas to the earth's surface as a product stream;
• and
• (f) means for conveying the permeate gas to the pressurizing means and means for conveying the gas pressurized by the pressurizing means to a discharge zone within the wellbore that is in fluid isolation from the feed side of the separation membrane.

A downhole fluid separation system comprising:

• (a) a casing having an interval that communicates with a gas producing zone so that gas from the producing zone enters the casing and a gas disposal zone so that waste gas separated from the gas enters the disposal zone;
• (b) a seal disposed in the casing wherein the seal is configured to separate the disposed zone from the producing zone;
• (c) a tubing string having at least one membrane module incorporated therein, said module having a feed side and a permeate side and being selective for one or more components of the multi-component fluid;
• (d) a monitoring device in the wellbore for detecting the pressure of the feed stream and the pressure of the permeate on the permeate side of the membrane;
• and
• (e) a pump for withdrawing gas from the permeate side and pressurizing the permeate gas to a pressure suitable for injection of the pressurized permeate gas into the disposal zone, said pump adjusting or reducing the pressure in response to the monitored and/or sensed pressure in the wellbore.