Not applicable.
1. Field of the Invention
The present invention relates to a system for producing hydrocarbons from multiple stages in a hydrocarbon production well. More specifically, the present invention relates to a multistage production system that associates a flapper valve assembly with each production valve assembly in the multistage system.
2. Description of the Related Art
During stimulation of a production zone (e.g., fracing) using a system incorporating multiple selectively-openable valve assemblies, the valve assembly furthest downwell is opened first with a shifting tool and a fracing material thereafter forced into the surrounding formation. The valve assembly is then closed and positive-pressure tested to insure system integrity before repeating the operation at the next upwell stage of the system. Positive pressure testing insures that the kinetic energy of the fracing material (i.e., fluid velocity) is concentrated at a single stage rather than egressing through another open (or partially open) stage. Focusing the kinetic energy of the fracing material at a single stage allows the fracing material to penetrate deeper into the formation, which results in greater effectiveness.
This process is repeated at each stage (i.e., through each valve) until the regions of the formation adjacent each of the stages have been stimulated. After this zonal stimulation, a shifting tool is again run through the production tubing and the valve assemblies are opened for production. This process, however, is time-consuming, and therefore expensive.
The present invention is a system and method for more efficiently and quickly producing from a production string. The present invention comprises production tubing; at least one selectively-openable valve assembly located inline with the production tubing; and at least one flapper valve assembly located inline with the production tubing. One flapper valve assembly is associated with each selectively-openable valve assembly. The flapper valve assembly is orientated to impede fluid flow in the downwell direction when closed.
A number of selectively-openable sliding valve assemblies 28a-28c and flapper valve assemblies 30a-30c are positioned inline with the production tubing 24. Each of the flapper valve assemblies 30a-30c is associated with and positioned upwell from one of the corresponding sliding valve assembly 28a-28c—that is, the first flapper valve assembly 30a is associated with and positioned upwell from the first sliding valve assembly 28a, the second flapper valve assembly 30b is associated with and positioned upwell from the second sliding valve assembly 28b, and the third flapper valve assembly 30c is associated with and positioned upwell from the third sliding valve assembly 28c. Each of the flapper valve assemblies 30a-30c is orientated to block fluid flow in the downhole direction when closed. While the preferred embodiment discloses three sliding valve assemblies 28a-28c, more or fewer sliding valve assemblies may be used. The entire production tubing 24, sliding valve assemblies 28a-28c, and flapper valve assemblies 30a-30c are surrounded with cement 32. Each of the selectively-openable sliding valve assemblies 28a-28c is mechanically actuatable with a shifting tool. U.S. Pat. No. 7,267,172 (issued Sep. 10, 2007) to Hofman describes one such specific embodiment of a mechanically actuatable shifting tool.
To initiate zonal stimulation, a shifting string 34 is run down the production tubing 24 with a first tool 36 adapted for actuating the flapper valve assemblies 30a-30c and a shifting tool 38 for opening the sliding valve assemblies 28a-28c. Prior to running the shifting string 34, each of the flapper valve assemblies 30a-30c is closed. The first tool 36 actuates the first flapper valve assembly 30a (see
After stimulation of the adjacent region 42 causing fracturing 44 of the production zone 14 proximal to the third valve assembly 28c, the shifting string 34 is positioned upwell to the second sliding valve assembly 28b. (
The present invention is described in terms of preferred embodiments in which a specific system and method are described. For example, while the present invention is described with respect to a cemented open lateral hole, the present invention can also be used in a cased vertical hole. Those skilled in the art will recognize that alternative embodiments of such system, and alternative applications of the method, can be used in carrying out the present invention. Other aspects and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims. Moreover, the recited order of the steps of the method described herein is not meant to limit the order in which those steps may be performed.
This application claims the benefit of U.S. provisional application Ser. No. 61/305,325 filed Feb. 17, 2010 and entitled Multistage Production System and Method, which is incorporated by reference herein.
Number | Date | Country | |
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61305325 | Feb 2010 | US |