System and method for fracturing a hydrocarbon producing formation

Abstract

A system and method for fracturing a hydrocarbon producing formation in which a tool assembly is inserted in a wellbore adjacent the formation, and fracturing fluid is introduced into the annulus between the tool assembly and the wellbore and flows to the formation.

Description

BACKGROUND

[0001] This invention relates to a system and method for fracturing a hydrocarbon producing formation with a fracturing system located in a wellbore adjacent the formation.

[0002] It is often necessary to selectively treat hydrocarbon zones, or formations, to extract hydrocarbons from the formation while isolating the formation from other intervals in a wellbore. Such treatments include perforating the well casing adjacent the formation and introducing a fracturing fluid through tubing into a tool assembly in the casing, and to a ported sub, or the like, connected in the tool assembly. The fluid discharges from the ported sub at a relatively high pressure and passes through the perforations in the well casing and into the formation to fracture it and promote the production of the hydrocarbons such as oil and/or gas. Often, the formation is isolated by setting packers above and below the ported sub to seal the zone during the fracturing operation.

[0003] However, these types of techniques are not without problems. For example, the use of a packer above the ported sub causes a high pressure differential between the formation and the area of the well above the packer, which may cause the packer to unset during operation, possibly resulting in unsuccessful fracture treatment, tool damage, and loss of well control.

[0004] Also, the introduction of fracturing fluid through the tubing and tool assembly creates additional problems, not the least significant of which is the fluid friction created by the passage of the fluid, which lead to mechanical failure of both the tubing and tool assembly. Thus, the diameter of the tubing must be optimized to allow maximum fluid rate and pressure subject to the constraints of weight, storage, and cost of large-diameter tubing.

[0005] Therefore, what is needed is a fracturing system and method that eliminates the above problems.

BRIEF DESCRIPTION OF THE DRAWING

[0006] The drawing is partial sectional/partial diagrammatic view of a system according to an embodiment of the invention.

DETAILED DESCRIPTION

[0007] Referring to the drawing, a tool assembly is referred to, in general, by the reference numeral 10 and is shown installed in a casing 12 disposed in a well. The casing 12 intersects a ground formation F which typically contains hydrocarbon fluids, and the tool assembly 10 is lowered to a predetermined depth in the casing 12 near the formation F and defines, with the casing 12, an annulus 14.

[0008] A packer 16 and a jet perforating sub 18 are connected in the tool assembly 10 in any conventional manner with the packer 16 extending downstream, or below, the sub 18. Although not shown in detail, it is understood that the packer 16 is adapted to form a seal across the annulus 14 and, as such, includes at least one packer element, which can be in the form of a torus fabricated from an expandable material surrounding a mandrel, and held in place in any conventional manner. The packer 16 also includes a mechanism or mechanisms to anchor the packer 16 in a position adjacent or near the formation F, after which the packer elements are expanded against the casing 12 to seal against axial fluid flow through the annulus 14 downstream of the packer 16. The packer 16 can be of any conventional design including those disclosed in assignee's U.S. Pat. Nos. 4,524,825, 4,590,995, 4,627,491, 4,697,640, 4,962,815, 5,701,954, and 6,056,052, all of which are incorporated in their entirety herein by reference.

[0009] The sub 18 contains a plurality of jet openings for discharging perforating fluid and fracturing fluid through the casing 12, through any cement between the casing 12 and the well, and into the formation F. The sub 18 can be of any conventional design including those disclosed in assignee's U.S. Pat. Nos. 5,499,678 and No. 5,765,642, both of which are incorporated in their entirety herein by reference.

[0010] Several other components, such as a blast joint, a centralizer, a release joint, and the like, can be provided in the tool assembly 10 upstream, or above, the sub 18 and between the sub 18 and a connector 20. Since these components are conventional, they are not shown, nor will they be described in detail. The connector 20 is connected to a section of coiled or jointed tubing 22 which is lowered in the well from the ground surface to locate the packer 16 and the sub 18 at a depth in the well in the vicinity of the formation F.

[0011] After the packer 16 and the sub 18 are positioned in the casing 12 in the above manner, they are set in a conventional manner so that the above-mentioned packer elements and anchor mechanisms engage the inner surface of the casing 12 to form a seal, as described above.

[0012] An abrasive fluid is then pumped from the ground surface, at a relatively high pressure, through the tubing 22. The abrasive fluid can include an abrasive particulate material, such as sand, suspended in a liquid, such as water, or chemically-treated water. The abrasive fluid flows to the sub 18 and discharges through the jet openings in the sub 18 and into the annulus 14 at a very high pressure and impacts against the inner surface of the casing 12 to form perforations 12a through the casing 12. It is understood that any cement extending between the casing 12 and the well will also be perforated in the above manner, and the perforations 12a thus created may penetrate into the formation F as well as forming indentation therein.

[0013] The flow of the abrasive fluid is then terminated, and the tool assembly 10 is cleaned in any conventional manner, such as by pumping cleaning fluid down the annulus 14 so that the cleaning fluid enters the lower portion of the tool assembly 10 and flows in a reverse direction upstream through the tool assembly 10, including the sub 18, and the tubing 22. In this context, it is understood that the sub 18 can be provided with a valve (not shown) that permits the flow of the abrasive fluid downstream through the sub and the jet openings as described above, but prevents the cleaning fluid that flows through the sub 18 in the opposite, or reverse, direction to discharge through the jet openings.

[0014] Fracturing is then commenced by pumping a conventional fracturing fluid, at a relatively high pressure, from ground surface down the annulus 14 in any conventional manner until the fracturing fluid penetrates the formation F, and, more particularly, the above-mentioned indentations in the formation F, to fracture the formation F and facilitate the extraction of oil and/or gas. The seal formed by the packer 16 permits this flow upstream of its location but prevents any fluid flow downstream.

[0015] Upon completion of this fracturing treatment, the flow of the fracturing fluid is terminated and the tool assembly 10 is again cleaned by pumping cleaning fluid down the annulus 14 so that the fluid enters the lower portion of the tool assembly 10 and flows upstream through the tool assembly 10, including the sub 18, and the tubing 22 in the manner described above.

[0016] Once the above operation is completed, the packer 16 can be released from its set position as described above, and the tubing 22, and therefore the tool assembly 10, can be moved axially in the casing 12 to another formation where the above method can be repeated. In this context, it is understood that the tool assembly 10 can include a circulation port to allow fluid circulation from the annulus 14 to the interior of the tool assembly 10 and the tubing 22 to promote the cleaning of the tool assembly 10. The preferred method for treating multiple formations is to sequentially treat the formations intersected by the well beginning with the lowest formation.

[0017] Flowing the fracturing fluid down the annulus and eliminating the use of an upper packer located above the sub 18 avoids the above-mentioned problems associated with introducing the fracturing fluid through a tubing and tool assembly utilizing an upper packer.

Variations and Equivalents

[0018] It is understood that variations may be made in the foregoing without departing from the scope of the inventions. For example, the type of packer and jet perforating sub can be varied. Also, the abrasive fluid, after perforating the casing, can flow to the formation F at very high pressure and form indentations, in the form of openings, bores, cracks, or the like, in the formation F to assist in the fracturing process. Further, the system described above is not limited to vertical wells, but is equally applicable to wells that deviate from the vertical. Moreover, the perforations in the casing can be formed by other methods, such as by using explosive charges. Still further, spatial references, such as “above”, “below”, “upper”, “lower”, “outer”, “over”, “between”, “inner”, and “vertical” are for the purpose of illustration only and do not limit the specific orientation or location of the structure or flow paths described above.

[0019] Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many other modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims.

Claims

1-21. (canceled)

22. A method for fracturing a formation adjacent a well having a casing disposed therein, comprising:

inserting a tool assembly in the casing to form an annulus between the tool assembly and the casing, the tool assembly including a plurality of jet openings;

forming a seal across the annulus below the jet openings to prevent fluid flow in the annulus downstream of the seal;

passing an abrasive fluid into the tool assembly for discharge through the jet openings and towards the casing to form perforations in the casing;

introducing a fracturing fluid into the annulus above the seal for flowing through the perforations and into the formation for fracturing the formation; and

introducing a cleaning fluid into the annulus for passing into the tool assembly for cleaning same.

23. The method of claim 22 wherein the cleaning fluid is introduced after the step of passing and before the step of introducing the fracturing fluid.

24. The method of claim 22 wherein the cleaning fluid is introduced after the step of introducing the fracturing fluid.

25. The method of claim 22 wherein the cleaning fluid is introduced after the step of passing and before the step of introducing the fracturing fluid; and further comprising introducing additional cleaning fluid into the annulus after the step of introducing the fracturing fluid.

26. The method of claim 22 wherein the cleaning fluid passes into the tool assembly through circulation ports formed in the lower portion of the tool assembly.

27. The method of claim 22 wherein the step of forming the seal comprises connecting a packer to the tool assembly, and setting the packer.

28. The method of claim 22 wherein the step of passing the abrasive fluid comprises the steps of:

connecting a sub to the tool assembly, the sub having the jet openings;

introducing the abrasive fluid to the sub; and

discharging the abrasive fluid through the jet openings towards the casing.

29. The method of claim 22 further comprising:

releasing the seal;

moving the tool assembly to another location in the well;

forming another seal across the annulus below the jet openings to prevent fluid flow in the annulus downstream of the seal;

passing additional abrasive fluid through the tool assembly and towards the casing to form perforations in the casing;

introducing additional fracturing fluid into the annulus for flowing through the perforations and into the formation at the new location for fracturing the formation; and

introducing cleaning fluid into the annulus for passing into the tool assembly for cleaning same.

30. A system for fracturing a formation adjacent a well having a casing disposed therein, the system comprising:

a tool assembly adapted to be located in the casing to form an annulus between the tool assembly and the casing;

a seal disposed on the tool assembly and adapted to extend across the annulus to prevent fluid flow in the annulus downstream of the seal;

means for passing an abrasive fluid through the tool assembly and towards the casing for forming perforations through the casing;

means for introducing a fracturing fluid into the annulus for flowing through the perforations and into the formation for fracturing the formation; and

means for introducing a cleaning fluid into the annulus for passage through the tool assembly for cleaning the tool assembly.

31. The system of claim 30 further comprising ports provided in the lower portion of the tool assembly for receiving the cleaning fluid.

32. The system of claim 30 wherein the tool assembly comprises a sub having jet openings through which the abrasive fluid is discharged.

33. The system of claim 30 wherein the seal is a packer.

34. The system of claim 33 wherein the packer can be set to form the seal and can be released to permit the tool assembly to be moved to another location in the well after which it is reset.