Top drive method and system for oil production
View Patent ↗Described herein are methods and systems for enhanced oil recovery (EOR). The methods and systems are especially suitable for enhancing oil recovery in bottom-water drive producing formations having a gas cap where coning of bottom water is a problem. An external gas such as natural gas is injected into the gas cap. This essentially eliminates the bottom water drive and replaces it with top gas drive. The amount of gas delivered is calculated to replace the volume of oil produced from the well and maintain a constant pressure at the gas-oil interface, which maintains horizontal thrust to the production point and maintains a stable oil-water interface, preventing coning. The methods expand the area of oil recovery.
1 . A method of recovering oil from a producing formation in the earth, wherein the producing formation is abutted on top by a gas cap and on bottom by an aquifer, the method comprising:
providing a production well extending through the producing formation,
providing a gas injection well extending into the gas cap,
injecting an external gas into the gas cap via the gas injection well at a controlled rate correlated to oil production such that (i) an injected gas volume at gas-cap conditions replaces the volume of produced oil and (ii) a gas-cap pressure is maintained within a predetermined threshold of an initial gas-cap pressure measured upon completion of the gas injection well, thereby providing sustained top-gas drive and maintaining horizontal hydraulic thrust across the producing formation, and
producing the oil via the production well at a production rate limited to a reservoir oil-transfer rate to perforations of the production well so as to maintain a stable oil-water interface and prevent bottom-water coning.
2 . The method of claim 1 , wherein the external gas comprises natural gas.
3 . The method of claim 1 , wherein the gas injection well is located about 40 to about 150 feet from the production well.
4 . The method of claim 1 , wherein the gas injection well terminates above an interface between the gas cap and the producing formation.
5 . The method of claim 1 , wherein the production well comprises:
a casing,
a production tubing configured within the casing,
a packer configured within an annulus between the casing and the production tubing, and
perforations in the casing providing fluid communication between the producing formation and the annulus.
6 . The method of claim 5 , wherein the perforations are configured within a bottom third of the producing formation.
7 . The method of claim 5 , wherein the perforations comprise upper perforations and lower perforations configured below the upper perforations.
8 . The method of claim 7 , wherein the packer is affixed to the production tubing and wherein the production tubing is configurable in a first position wherein the packer does not block the upper perforations and in a second position wherein the packer blocks the upper perforations.
9 . The method of claim 8 , wherein producing oil comprises:
producing oil for a first duration with the tubing in the first position,
switching the tubing from the first position to the second position, and
producing oil for a second duration with the tubing in the second position.
10 . The method of claim 7 , wherein the lower perforations are located about 12 to about 18 inches above an oil-water interface between the producing formation and the aquifer.
11 . The method of claim 1 , wherein injecting the external gas comprises injecting an amount of external gas adequate to provide lift of oil within the producing formation.
12 . The method of claim 1 , wherein producing the oil comprises producing the oil at a rate that eliminates bottom-water coning.
13 . The method of claim 1 , wherein the injected gas volume is determined by:
measuring an initial gas-cap pressure when the gas injection well is completed;
monitoring a volume of oil produced from the producing formation over a production interval; and
injecting an amount of external gas into the gas cap, at gas-cap conditions, calculated to equal the volume of oil produced during the production interval so as to maintain the gas-cap pressure within a predetermined threshold of the initial gas-cap pressure.
14 . The method of claim 1 , wherein maintaining the gas-cap pressure comprises:
measuring a gas-cap pressure when the gas injection well is completed to establish an initial gas-cap pressure;
monitoring gas-cap pressure during oil production; and
controlling injection of the external gas into the gas cap such that the monitored gas-cap pressure is maintained within a predetermined threshold of the initial gas-cap pressure throughout production.
15 . The method of claim 1 , wherein producing the oil at the production rate limited to the reservoir oil-transfer rate comprises:
determining a rate of migration of oil within the producing formation to the production perforations based on reservoir characteristics; and
controlling a production rate of the production well to not exceed the determined oil-migration rate so as to maintain a stable oil-water interface within the producing formation and inhibit upward movement of water from the aquifer toward the production perforations.
16 . The method of claim 1 , wherein producing the oil at the production rate limited to the reservoir oil-transfer rate comprises:
monitoring a position of an oil-water contact within the producing formation over time; and
adjusting the production rate of the production well in response to the monitored oil-water contact position such that the oil-water contact remains stationary relative to the production perforations, thereby inhibiting bottom-water coning.