1. Field of the Invention
The invention disclosed and claimed in this application relates to the treatment of oil and/or gas wells. One example of such treatment is commonly referred to as fracturing the formulation around an oil or gas well. Fluid with certain chemical additives and a proppant are injected into the formation surrounding either a vertical or horizontal well to form cracks or passageways in the formation to stimulate the production of the well.
2. Description of Related Art
Currently there are several techniques utilized to stimulate producing of a well by fracing. Typically a packer or plug is utilized to isolate a particular portion of the well and the fracing fluid is injected into the isolated portion under high pressure. Once a given portion of the well is treated in this manner, a second zone uphole of the first zone is isolated by a second packer or plug that cuts off flow to the downhole portion of the well that has been treated.
U.S. Pat. No. 7,322,417 discloses a plurality of vertically spaced production layers 1 and a plurality of valves 14. A ball is captured on a valve seat 94 which will cause an increase in pressure to open valve 14. This allows fracturing fluids to enter the annular region that surrounds the valve. The balls may be formed of a dissolvable or frangible material, which allows the ball to be dissolved or eroded to open up communication upstream through the casing.
U.S. Pat. No. 7,134,505 discloses a similar system in which a plurality of spaced apart packers 20a-n and a plurality of valve bodies 26c-n that capture balls of varying diameters to selectively open ports 16c-e to allow fracturing fluids to flow into the isolated zones.
Stage frac methods include the use of pump down bridge plugs, perforating guns, and sliding sleeves. The current pump down method requires a drill out phase after frac with coiled tubing or jointed pipe. This is an expensive and time consuming process which involves additional risk of the coil tubing getting stuck in the wellbore. This time and operational risk is a significant impact item on the overall economics of oil and gas projects.
Sliding sleeves require that their exact position needs to be known as the casing is run into the well. The number of frac initiation points is limited and the cost is significant for each sleeve. Sleeves may malfunction either during opening or closing. Higher risk comes from incomplete frac distribution and limited reservoir drainage.
The present invention overcomes the difficulties with the prior art as described above by using proven concepts and a simplified approach. An expansible valve seat or stop member that can be run on wireline (pump-down, tractor, tubing or coiled tubing) is positioned at predetermined locations along the casing and is expanded for example by a shaped charge or with a mandrel extrusion process. A disintegrating or dissolvable ball can be dropped in the valve seat to isolate a portion of the well to allow for fracturing of the isolated portions of the well. The seat may be made of the same material as the ball so that the drill out step is completely eliminated.
The ball and valve seat become the frac plug that would normally be pumped down in a conventional horizontal pump-down process.
The casing can be perforated as in the pump down method and fracing can be initiated once the ball seals on the valve seat. A dart may be used in lieu of a ball. Balls, darts, seats or sleeves may be soluble, dissolvable or frangible.
As described below, the invention of this application is directed to a novel process of fracturing a plurality of zones in the formation surrounding a horizontal or vertical well without the use of multiple bridge plugs or frac plugs that require drill out after the fracturing process is complete prior to the production stage.
This is accomplished in the following manner. After the well has been drilled (51) and the casing has been fully positioned (52), an expansible sleeve such as shown in
Expansible sleeve 10 may be precisely positioned within the casing by any suitable known technique such as a line counter or collar locator. Once positioned within the desired location of the casing, the cord is detonated causing the sleeve to expand outwardly against the inner surface of the casing (54). In so doing, the sleeve forms a seat 12 as shown in
Once the tube 11 and seat have been set in place, the casing and cement (if present) in the first frac zone can be perforated (55) in the conventional way by a perforating gun on the same tool-string as the expansible sleeve. At this point the tool-string can be removed, and the fracing process can be initiated by pumping down (56) a ball or dart to rest against seat 12. This will prevent the fracing fluid from flowing downhole and will cause the fracing fluid under pressure (57) to enter the formation surrounding the perforations in the casing and thus commence the fracing process.
Once the process is completed for the first zone, a second expansible sleeve can be placed (58) to isolate a second zone and the process can be repeated (59-62) for as many zones as desired as indicated in
Another embodiment of the expansible sleeve is illustrated in
An additional embodiment of the expansible sleeve is illustrated in
The expandable sleeve may be formed of steel for example J-55 or similar steel. The wall thickness may vary from approximately 0.095 inches to about 0.25 inches. The diameter of the sleeve is selected to be slightly smaller than that of the well casing so for example if the casing is 5½ inch casing, the sleeve may have an outside diameter of 4.5 inches.
Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.