Wells – Processes – Producing the well
Reexamination Certificate
1999-05-17
2001-01-16
Tsay, Frank (Department: 3672)
Wells
Processes
Producing the well
C166S373000, C166S308400
Reexamination Certificate
active
06173783
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of drilling for hydrocarbons such as oil and gas. More specifically, this invention relates to a method for completing and producing hydrocarbons through the use of extreme overbalance pressure followed by an underbalance surge.
BACKGROUND OF THE INVENTION
When drilling for hydrocarbons such as oil and gas in a subterranean formation, a wellbore is drilled into the formation for the purpose of gaining access to the hydrocarbons. Drilling mud is often used to assist in the drilling process and to hydrostatically suppress the flow of fluids into the well from a pressurized formation. A casing is installed and cemented to the face of the wellbore. During this process the drilling mud is, for the most part, replaced with water. The casing blocks the flow of fluid from the formation into the wellbore. Charges are then detonated so as to cause perforations in the well casing and cement. These perforations extend into the formation and permit the influx of the hydrocarbons into the well. The perforation is typically carried out using a perforating gun.
Perforation can be conducted in “overbalanced” conditions where the well pressure is greater than the pressure at which the formation will fracture. The term “underbalance” is used to refer to a situation where the pressure of liquid in the wellbore is less than the pressure existing in the formation.
After the perforations have been created, the drilling mud is gradually displaced by the influx of hydrocarbons and the hydrocarbons eventually flow into the wellbore and then up to the surface.
Conventional drilling methods and assemblies suffer from certain disadvantages. For example, it can be problematic to clean the perforations of mud filtrate, cement contaminates and perforation debris. In standard extreme overbalance perforating applications it is not possible to surge the well prior to flowing the well back to surface.
These and other deficiencies in the prior art have been addressed by the present invention.
SUMMARY OF THE INVENTION
In a first aspect, the present invention provides a method of completing and producing hydrocarbons in a well, the well having a casing string extending into a wellbore and penetrating a hydrocarbon-bearing formation, a tubing string extending downhole into the casing string, the strings forming an annulus between them which annulus is sealed in one portion by a packer, the tubing string having a bore and ports in its surface located downhole of the packer, the tubing string having valve means located downhole of the ports for selectively trapping or releasing pressure in the tubing string downhole of the valve means, means for perforating the casing string being located at the tubing string's lower end and downhole of the valve means, the casing string initially blocking communication of the hydrocarbons with the wellbore, the method comprising: blocking the ports in the tubing string so as to prevent fluid communication between the casing string and the tubing string; creating a fluid column in the tubing string's lower end; adding a sufficient volume of a gas to the fluid column to achieve a predetermined downhole pressure which will exceed the fracture gradient of the formation; perforating the casing at the hydrocarbon-bearing formation so as to fracture the formation; maintaining pressure below the packer through the use of the valve means; removing sufficient volumes of the gas from the well so that it is in an underbalanced state; opening the ports so as to release the pressure below the packer and allow it to surge into the tubing string, thus permitting a mixture of hydrocarbons and gas to surge up the tubing string to the surface.
The gas used may be nitrogen, carbon dioxide or any other suitable gas. The valve may comprise a flapper valve. If desired, an additional volume of gas may be pumped into the tubing string after perforation to further fracture the formation.
REFERENCES:
patent: 3613792 (1971-10-01), Hyde et al.
patent: 3706344 (1972-12-01), Vann
patent: 3800705 (1974-04-01), Tamplen
patent: 4554981 (1985-11-01), Davies
patent: 5971069 (1999-10-01), Stoy et al.
Abbott-Brown John
Zemlak Jim
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