Completing wells in unconsolidated formations

Abstract

A method of completing an unconsolidated formation by first injecting a curable resin into diametrically-opposed zones within the formation and then allowing the resin to set to form a consolidated mass in these zones. Once the resin has set, the consolidated zones are hydraulically fractured to establish fluid communication between the untreated area of the formation outside these zones and the wellbore. Preferably, the fracturing fluid carries resin-coated proppants which, when set, form a permeable mass within the fractures to thereby allow flow of fluids through the fracture while preventing flow of sand.

Description

DESCRIPTION

[0001] 1. Technical Field

[0002] The present invention relates to a method for completing a well in an unconsolidated formation and in one of its aspects relates to a method for completing a well in an unconsolidated formation wherein a zone within the formation is consolidated by injecting a curable resin and then fractured once the resin has set to thereby provide fluid communication between the untreated formation and the wellbore.

[0003] 2. Background of the Invention

[0004] In producing hydrocarbons or the like from loosely or unconsolidated subterranean formations, it is not uncommon to produce large volumes of particulate material (e.g. sand) along with the formation fluids. This “sand production” routinely causes a variety of problems which result in added expense and substantial downtime. For example, the produced sand may cause (1) severe erosion and premature wearing of the well tubing and other production equipment; (2) clogging of the flow from the well which requires a workover of the well; (3) extra processing of the produced fluids at the surface to remove and dispose of the sand; (4) caving of the formation, etc. Accordingly, it is extremely important to control the production of sand from such wells.

[0005] There are several techniques that are well known for controlling “sand production” from unconsolidated formations. One such known technique involves injecting a consolidating agent, e.g. curable resin, into the formation to stabilize the area of the formation which lies near the wellbore. The resin is injected, in its uncured state, through the wellbore into the near-wellbore area of the formation where it coats and bonds the grains of sand together to form a solidified matrix around the wellbore. In the prior art consolidated treatment, a postflush liquid is then injected into the formation to displace the resin from the pore spaces formed between the bonded grains of sand within the matrix, thereby restoring some permeability to the treated area through which the formation fluids can flow through the matrix and into the wellbore.

[0006] While such techniques have been widely used, unfortunately, they experience some major drawbacks. For example, since this type of consolidation treatment is usually carried out in a well having an “open hole” completion (i.e. wellbore is uncased adjacent formation to be treated), there is always uncertainty of whether or not the resin has uniformly penetrated into the formation which surrounds the wellbore. In other words, there is no assurance that the bulk of the resin did not merely flow into the formation at one point adjacent the wellbore (i.e. path of least resistance) while leaving the areas around the wellbore virtually untreated. This is obviously undesirable, if not unacceptable, since substantial amounts of sand may still be produced from the untreated areas of the formation abutting the wellbore thereby significantly defeating the overall benefits of the consolidation treatment.

[0007] Further, the actual amount of permeability which exists in the consolidated matrix once the resin has cured is difficult to predict and is often substantially less than expected and, in some cases, is not adequate for commercial production. In such instances, the treatment may have to be repeated or some other workover performed before the well will produce at satisfactory rates.

SUMMARY OF THE INVENTION

[0008] The present invention provides a method of completing an unconsolidated, subterranean formation by treating zones of the formation with a consolidating agent, e.g. curable resin, wherein (a) the injection of the resin is controlled to insure proper placement of the resin and (b) the final permeability of the consolidated zone is assured whereby flow of formation fluids can flow into the wellbore while flow of sand is prevented. Basically, in the present method, a curable resin is injected into selected zones and is allowed to set to form a consolidated mass within these zones. These zones are then hydraulically fractured to establish fluid communication between the untreated area of the formation and the wellbore and are propped by proppants, preferably resin-coated.

[0009] More specifically, a wellbore is drilled through the formation and is cased with a string of casing. Two sets of openings (e.g. perforations, slots, etc.) are formed in the casing diametrically-opposed to each other with each set of openings lying substantially adjacent the natural fracture plane of the formation. A consolidating agent, e.g. a curable resin, is injected down the wellbore and out into the formation through the opposed sets of openings in the casing and form two zones in the formation which lie adjacent the respective sets of openings. The resin is allowed to set and cure in these zones to become consolidated masses around the respective sets of openings. Preferably, the resin is a thermosetting resin which is cured by the temperature in the formation.

[0010] Once the resin has hardened, a fracturing fluid is pumped under pressure down the wellbore and out through the same respective sets of opposed openings in the casing to thereby create a fracture through the respective consolidated zones and thereby establish fluid communication between the untreated area of the formation outside of the zones and said wellbore. Preferably, the fracturing fluid contains proppants which are resin-coated so that once the proppants are placed in the fractures by the fracturing fluid, the resin on the proppants sets and cures to bind the proppants together into a consolidated, permeable mass within the fractures. This permeable mass of bonded proppants allows fluids from the untreated areas of the formation to flow into the wellbore while acting as a filter in preventing flow of sand therethrough.

[0011] By injecting the consolidating agent through diametrically-opposed openings in the well casing, its placement will be controlled so that it flows into those areas of the formation which are to be treated. Further, by subsequently fracturing only the treated zones within the formation, only the desired production fluids can flow from the untreated areas of the formation into the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The actual construction, operation, and apparent advantages of the present invention will be better understood by referring to the drawings which are not necessarily to scale and in which like numerals identify like parts and in which:

[0013] FIG. 1 is a plan, cross-sectional view of a cased wellbore at a point adjacent an unconsolidated formation to be completed illustrating an initial step of the method of the present invention;

[0014] FIG. 2 is the plan, cross-sectional view of FIG. 1 after an intermediate step of the present invention has been carried out; and

[0015] FIG. 3 is the plan, cross-sectional view of FIG. 2 after the formation has been completed in accordance with the present invention.

[0016] While the invention will be described in connection with its preferred embodiments, it will be understood that this invention is not limited thereto. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents which may be included within the spirit and scope of the invention, as defined by the appended claims.

BEST KNOWN MODE FOR CARRYING OUT THE INVENTION

[0017] Referring more particularly to the drawings, FIG. 1 illustrates a cross-sectional, plan view of wellbore 10 which has been drilled from the surface (not shown) through an unconsolidated production formation 11. As will be understood by those skilled in the art, wellbore 10 has been cased and cemented with casing 12 and cement 13 through formation 11. In carrying out the method of the present invention, openings 14 are formed through casing 12 and cement 13 at point(s) adjacent formation 11 to thereby provide fluid communication between the formation and wellbore 10. Openings 14 comprise two set of openings which are formed diametrically-opposed from each other in casing 13 and are positioned to lie substantially on the natural fracture plane of the formation.

[0018] Preferably, these openings are perforations which are formed by a standard 180° perforating gun which, in turn, has been oriented with respect to the fracture planes of formation 11 by commercially-available techniques. Alternatively, the sets of opposed openings 14 can be slots formed by standard, known hydrojetting techniques. The forming of the opposed openings 13, either by perforating or by hydrojetting, will also aid in initiating a single bi-wing fracture when the formation is subsequently hydraulically-fractured as will be more fully explained below.

[0019] Next, a consolidating agent is injected down a workstring (not shown) within wellbore 10 and into formation 11 through openings 14 in casing 13. The consolidating agent may be any substance which can be placed in its liquid state and then hardens to bond the sand grains of the formation into a solid-like mass. Preferably, the consolidating agent is a curable resin, e.g. thermo-setting epoxy, phenolic, furan, polyurethane, or the like and a curing agent, if necessary, as is known in the art. The resin flows out through the opposed openings 14 and coats the sand grains into zones 15 of formation 11 on either side of casing 13 as shown in FIG. 2. When the desired volume of resin has been injected, it is allowed to set and cure (e.g. under the influence of the formation temperature) to thereby form a consolidated mass within zones 15 which lie adjacent said openings 14.

[0020] Once the resin has cured, a typical fracturing fluid, e.g. cross-linked polymer gel, is pumped down a workstring (not shown) and out into zones 15 through openings 14 in casing 13 to “hydraulically fracture” zones 15. The fracturing fluid is pumped at a pressure sufficient to create the bi-winged fracture 16 in the respective zones 15 on either side of the casing as illustrated in FIG. 3. It is preferred that the fracturing fluid carry particulate material (e.g. large grain sand having 8-60 mesh size) which act as proppants to keep fractures 16 open when the fracturing pressure is relieved.

[0021] Further, preferably, the particulate material is resin-coated proppants, either pre-coated or “coated on-the-fly”, so that once placed in the fractures 16, the resin on the proppants sets and cures to bind the proppants together into a consolidated, permeable mass within the fractures 16. This permeable mass of bonded proppants serves to fluidly connect the untreated, unconsolidated areas of formation 11 outside of consolidated zones 1b to the wellbore 11 by allowing flow of fluids therethrough while acting as a filter in preventing flow of sand therethrough.

Claims

1. A method of completing an unconsolidated, subterranean formation through a wellbore, said method comprising:

injecting a consolidating agent through said wellbore and into at least one zone within said formation to form a consolidated mass therein; and

fracturing said consolidated mass with a fracturing fluid to establish fluid communication between the area of said formation outside of said zone and said wellbore.

2. The method of claim 1 wherein said consolidating agent is a curable resin.

3. The method of claim 2 wherein said resin is selected from the group consisting of thermo-setting epoxy, phenolic, furan, and polyurethane.

4. The method of claim 1 wherein said fracturing fluid contains proppants.

5. The method of claim 4 wherein said proppants are resin-coated.

6. A method of completing an unconsolidated subterranean formation through a wellbore, said method comprising:

casing said wellbore with a casing;

forming openings in said casing adjacent said formation;

injecting a consolidating agent down said wellbore into said formation through said openings in said casing;

allowing said consolidating agent to set to form consolidated zones within said formation which lie adjacent said openings in said casing; and

injecting a fracturing fluid through said openings in said casing to fracture said consolidated zones and thereby establish fluid communication between the untreated area of said formation outside said consolidated zones and said wellbore.

7. The method of claim 6 wherein said openings comprise:

two sets of openings formed in said casing and spaced diametrically-opposed from each other.

8. The method of claim 7 wherein said two sets of openings are positioned adjacent the natural fracture plane of said formation.

9. The method of claim 7 wherein said openings are perforations through said casing.

10. The method of claim 7 wherein said openings are slots through said casing.

11. The method of claim 7 wherein said consolidating agent is a curable resin.

12. The method of claim 11 wherein said resin is selected from the group consisting of thermo-setting epoxy, phenolic, furan, polyurethane

13. The method of claim 11 wherein said curable resin is injected into said formation through each of said two sets of openings in said casing to form respective consolidated zones in said formation adjacent said sets of openings.

14. The method of claim 13 wherein said fracturing fluid contains proppants.