INDIRECT HYDRAULIC FRACTURING METHOD AND SYSTEM

Description

FIELD OF THE INVENTION

The present invention relates to methods and systems for indirectly fracturing subterranean wells and well laterals for increased production.

BACKGROUND OF THE INVENTION

Hydrocarbon fluids such as oil and natural gas are obtained from hydrocarbon-bearing subterranean formations by drilling wells that penetrate the formations. Hydraulic fracturing is a procedure used in hydrocarbon bearing formations, and in other formations, for improving well productivity by placing or extending channels from the wellbore into the formation.

When conducting a hydraulic fracturing operation, a hydraulic fracturing fluid is pumped into the subterranean formation under sufficient pressure to create, expand, and/or extend fractures in the formation and to thus provide enhanced recovery of the formation fluid. Hydraulic fracturing fluids typically comprise water and sand, or other proppant materials, and also commonly include various types of chemical additives.

A need exists for new and improved procedures and systems for fracturing shale fields and other types of formations which will reduce fracturing costs and will be more efficient for stimulating the formations and producing oil, gas, and/or other products. The improved hydraulic fracturing procedures and systems will preferably: (a) reduce the amount of fracturing fluid and the amount of proppant material required and (b) reduce other operational costs.

The improved hydraulic fracturing procedure and system will also preferably be effective for (i) indirectly fracturing adjacent wells, (ii) indirectly fracturing adjacent laterals of horseshoe wells, (iii) indirectly fracturing adjacent laterals in other types of wells having multiple laterals, (iv) indirectly fracturing new wells, (v) indirectly fracturing or refracturing old wells which may or may not have been shut-in and may or may not have been previously fractured, and (vi) producing fracture and flow interactions between adjacent wells, or within a pattern of wells, in a production field.

SUMMARY OF THE INVENTION

The present invention provides an indirect fracturing procedure and an indirect fracturing system which address the needs identified above. In the inventive indirect fracturing procedure and system, the amount of fracturing fluid, the amount of proppant, and the operational costs required for fracturing adjacent wells, or adjacent laterals of the same well, can be significantly reduced.

The inventive indirect fracturing procedure and system are also effective for (i) increasing the efficiency of producing hydrocarbon products from shale fields, (ii) increasing the efficiency of producing hydrocarbons, water, mineral solutions, or other products from other types of subterranean formations, (iii) indirectly fracturing new wells, (iv) indirectly fracturing or refracturing old wells which may have been shut-in and may or may not have been previously fractured, and (v) producing fracture and flow interactions between adjacent wells, or within a pattern of wells, in a formation or production field.

In one aspect, there is provided a method of indirect hydraulic fracturing which preferably comprises a step (a) of providing at least a first wellbore interval and a second wellbore interval, different from the first wellbore interval, in a subterranean formation. The first wellbore interval preferably has a casing or liner therein and one or more clusters of openings are provided through the casing or liner. The second wellbore interval is preferably positioned and oriented with respect to the first wellbore interval so that hydraulic fractures initiated through at least some of the openings of the one or more clusters of openings of the first wellbore interval will propagate toward and will at least reach the second wellbore interval. The hydraulic fractures which reach the second wellbore interval are interacting hydraulic fractures.

In another aspect, in addition to step (a), the method can also include the steps of: (b) isolating one or more longitudinal sections of a predicted interaction zone of the second wellbore interval in which it is predicted that the interacting hydraulic fractures initiated from the first wellbore interval will interact with the second wellbore interval, the one or more longitudinal sections being isolated by positioning a series of two or more isolation devices in the second wellbore interval; and (c) pumping a fracturing fluid into the first wellbore interval to produce the interacting hydraulic fractures and propagate the interacting hydraulic fractures at least as far as the second wellbore interval.

In another aspect, the method can optionally comprise: (i) the second wellbore interval being a wellbore interval of a well; (ii) the well having a wellhead for production from the well; and (iii) at least one of the isolation devices positioned in the second wellbore interval in step (b) being positioned in the well at a location between the predicted interaction zone of the second wellbore interval and the wellhead to prevent the fracturing fluid pumped into the first wellbore interval in step (c) from flowing from the second wellbore interval to the wellhead.

In another aspect, the method can optionally comprise: (i) the one or more clusters of openings provided through the casing or liner of the first wellbore interval being a longitudinal series of two or more of the clusters of openings; (ii) there being a cluster spacing distance between each adjacent pair of the clusters of openings in the longitudinal series of two or more clusters of openings in the first wellbore interval; (iii) at least one said cluster spacing distance between an adjacent pair of the clusters of openings being a maximum cluster spacing distance; (iv) the series of two or more isolation devices positioned in the second wellbore interval in step (b) being a series of at least three of the isolation devices; and (v) no adjacent ones of the isolation devices in the series of at least three isolation devices being spaced a distance apart which is more than the maximum cluster spacing distance.

In another aspect, the method can optionally comprise pumping an amount of the fracturing fluid into the first wellbore interval in step (c) sufficient to propagate hydraulic fractures from and beyond the second wellbore interval in a direction away from the first wellbore interval.

In another aspect, the method can optionally comprise: (i) providing a proppant material in one or more of the one or more longitudinal sections of the second wellbore interval which are isolated in step (b) and (ii) the proppant material provided in the one or more sections of the second wellbore interval being carried by the fracturing fluid into the hydraulic fractures which are propagated from and beyond the second wellbore interval in the direction away from the first wellbore interval.

In another aspect, the method can optionally comprise: (i) also providing a third wellbore interval, different from the first wellbore interval and the second wellbore interval, in the subterranean formation and (ii) the third wellbore interval being positioned and oriented with respect to the second wellbore interval so that at least some of the hydraulic fractures propagated from and beyond the second wellbore interval in a direction away from the first wellbore interval propagate toward and at least reach the third wellbore interval, the hydraulic fractures which reach the third wellbore interval being secondary interacting hydraulic fractures.

Further aspects, features, and advantages of the present invention will be apparent to those in the art upon examining the accompanying drawings and upon reading the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a first embodiment of the indirect fracturing system of the present invention which includes a directly fractured first wellbore interval 14 and an indirectly fractured second wellbore interval 18.

FIG. 2 schematically illustrates a second embodiment of the indirect fracturing system of the present invention which further includes an indirectly fractured third wellbore interval 40.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of a well system 2 in which the inventive indirect fracturing procedure and system are used is illustrated in FIG. 1. The well system 2 is a deviated or horizontal horseshoe-type well comprising: an above-ground wellhead assembly 4 provided at a surface location; a vertical section 5 of a wellbore 6 which extends downwardly form the wellhead assembly 4 to a subterranean formation 8; and a deviated or horizontal lateral section 10 of the wellbore 6 which deviates and extends from the bottom of the vertical section 5 of the wellbore 6 (i.e., from the heel 12 of the deviated well 2) into the subterranean formation 8. The deviated or horizontal lateral section 10 of the horseshoe well 2 can be at any angle from vertical and preferably has a U shape.

The horseshoe-shaped lateral section 10 of the well 2 preferably comprises: (i) a first wellbore interval 14 which extends in a first direction 16 away from the vertical wellbore 5; (ii) a second wellbore interval 18, spaced apart from the first wellbore interval 14, which extends in a second direction 20 which is preferably substantially opposite the first direction 16; and (iii) a curved or U-shaped wellbore interval 22 which extends from the distal end of the first wellbore interval 14 to the proximal end of the second wellbore interval 18.

In the inventive method and system, a hydraulic fracturing procedure will be performed in the first wellbore interval 14 which will both (a) directly stimulate the first wellbore interval 14 and (b) indirectly fracture the second wellbore interval 18. In order to indirectly fracture the second wellbore interval 18, the second wellbore interval 18 will be positioned and oriented with respect to the directly fractured wellbore interval 14 such that at least some hydraulic fractures 24 initiated in and emanating from the directly fractured wellbore interval 14 will propagate toward, and will extend at least as far as and interact with the indirectly fractured wellbore interval 18. These hydraulic fractures 24 are referred to herein as the interacting hydraulic fractures.

It will also be understood that although the first wellbore interval 14 is described herein as being directly fractured and the second wellbore interval 18 is described as being indirectly fractured, the procedure could be reversed, at least in some types of wells, such that first wellbore interval 14 rather than the second wellbore interval 18 is indirectly fractured.

Although other positioning arrangements can alternatively be used, the directly fractured wellbore interval 14 and the indirectly fractured wellbore interval 18 will preferably be positioned together in a plane of symmetry corresponding to, and which takes advantage of, the stress planes or other dominant fracturing characteristics of the subterranean formation 8. The stress planes and/or other dominant geological features of the formation 8 can be determined prior to drilling using, e.g., data obtained from a pilot well or from a previous well, core samples, sonic logs, microseismic data, imaging tools such as image logs, or fiber-base micro-seismic, or tiltmeter data. The indirectly fractured wellbore interval 18 will most preferably be substantially parallel to the directly fractured wellbore interval 14 such that directly fractured wellbore interval 14 and the indirectly fractured wellbore interval 18 are on opposite sides of and are equidistant from an axis of symmetry 26.

Although the directly fractured wellbore interval 14 and the indirectly fractured wellbore interval 18 are depicted in FIG. 1 as being wellbore intervals formed on opposite sides of the U-shaped lateral 10 of a single horseshoe well 2, it will be understood that the directly fractured wellbore interval 14 and the indirectly fractured wellbore interval 18 can alternatively be adjacent wellbore intervals located in other types of wells or laterals. By way of example, but not by way of limitation, the directly fractured wellbore interval 14 and the indirectly fractured wellbore interval 18 can alternatively be, or can be included in, (i) adjacent, spaced apart laterals which extend from the same vertical wellbore, (ii) adjacent, spaced apart laterals which extend from a common wellbore lateral, (iii) vertical wellbore intervals of two separate vertical wells, or (iv) wellbore intervals of two separate deviated or horizontal wells.

It will also be understood that the either or both of the directly fractured wellbore interval 14 and the indirectly fractured wellbore interval 18 can be a wellbore interval which is located in (i) a new well, (ii) an existing well which is currently in operation, or (iii) an existing well which was shut-in. In addition, the directly fractured wellbore interval 14 and/or the indirectly fractured wellbore interval 18 can be a wellbore interval which has, or has not, been previously fractured. Preferably, the directly fractured wellbore interval 14 will not have been previously fractured and most preferably neither the directly fractured wellbore interval 14 nor the indirectly fractured wellbore interval 18 will have been previously fractured.

For the direct fracturing operation in the first wellbore interval 14, the wellbore interval 14 will preferably have a casing or liner therein wherein one or more clusters of perforations, slots, or other openings have been formed through the casing or liner for discharging the fracturing fluid into the subterranean formation 8. As one example, if a cemented casing is used in the directly fractured wellbore interval 14, the perforations or other openings will be formed through both the casing and the cement. As another example, if a slotted liner is used, a pair of swell-packers or other exterior isolation devices can be positioned between the exterior of the liner and the wall of the borehole at the opposing ends of each fracturing stage in order to isolate the exterior of the liner in the fracturing interval during the fracturing operation.

The directly fractured wellbore interval 14 can be fractured in one or more fracturing stages 30a, 30b. For each fracturing stage 30a or 30b, usually after the fracture treatment, the interior of the casing or liner at the upper and/or lower ends of the fracturing stage 30a or 30b can be isolated or blocked as needed using, e.g., reverse flow-through plugs, cast-iron bridge plugs, solid non-flow-through plugs, or sand plugs. In conducting the fracturing operation in the directly fractured wellbore interval 14, the fracturing fluid can be delivered to each fracturing stage 30a, 30b using, e.g., bullhead pumping or coil-tubing operations.

The clusters of openings provided through the casing or liner of the directly fractured wellbore interval 14 will preferably comprise a longitudinal series of two or more clusters wherein each adjacent pair of clusters will be spaced apart by a cluster spacing distance 32. For a series of three or more clusters, the cluster spacing distances 32 between the adjacent pairs of clusters can be the same or different. One or more or all of these cluster spacing distances 32 will be a maximum cluster spacing distance, which is the longest distance between any adjacent pair of the clusters. In addition, the average of all of cluster spacing distances 32 will be referred to herein as the average cluster spacing distance. By way of example, but not by way of limitation, the distance between any given pair of adjacent clusters of openings in the directly fractured wellbore interval 14 will preferably be in the range of from about 10 feet to about 40 feet. As used herein and in the claims, the term “about” means±10%.

In addition to determining the relative locations of the first and second wellbore intervals 14 and 18 for the indirect fracturing procedure, the locations of the stress planes and other geological data and information gathered for the subterranean formation 8 will also be used to determine a predicted interaction zone 34 for the indirectly fractured wellbore interval 18. The predicted interaction zone 34 is the segment or portion of the indirectly fractured wellbore interval 18 in which it is predicted that the interacting hydraulic fractures initiated from the directly fractured wellbore interval 14 will interact with the indirectly fractured wellbore interval 18.

The indirectly fractured wellbore interval 18 can be an open wellbore interval with no casing or liner therein. Alternatively, the indirectly fractured wellbore interval 18 can have a slotted liner therein or a perforated casing.

The indirectly fractured wellbore interval 18 will preferably have a liner therein wherein one or more sections of slots or other openings are provided through the wall of the liner. The slots intervals or perforated intervals in the indirectly fractured wellbore interval 18 can be aligned with the plane of the fracture in the indirectly fractured interval 18 with higher shot density in the region where an intersection is expected.

Prior to the indirect fracturing procedure, if a liner is used in the indirectly fractured wellbore interval 18, two or more exterior isolation devices, depending upon the number of indirect fracturing stages used in the indirectly fractured wellbore interval 18, will preferably be positioned between the exterior of the liner and the wall of the borehole of the wellbore interval 18 in order to block fluid flow in the annulus outside of the liner. Examples of suitable exterior isolation devices include, but are not limited to, swell-packers and blast joints. The exterior isolation devices will preferably be swell-packers.

For a single indirect fracturing stage, two swell-packers will preferably be used. One of the swell-packers will preferably be positioned at or beyond a first longitudinal end of the one or more sections of slots or other openings provided through the wall of the liner in the indirect fracturing interval. The other swell-packer will preferably be positioned at or beyond a second longitudinal end, opposite the first longitudinal end, of the one or more sections of slots or other openings provided through the wall of the liner in the indirect fracturing interval.

In addition to any swell-packers or other exterior isolation devices which may be required in the case of a liner, one or more interior longitudinal sections 35 of the liner, casing, or open borehole in the predicted interaction zone 34 of the indirectly fractured wellbore interval 18 will also preferably be isolated by positioning a series of two or more interior isolation devices 36 in the indirectly fractured wellbore interval 18. Examples of interior isolation devices 36 suitable for use in the second wellbore interval 18 include, but are not limited to, hard plugs, sand plugs, bridge-plus reverse flow through plugs, or cast-iron bridge plugs. The isolation devices 36 will preferably be hard plugs. These can, for example, be run with casing during casing operations.

The series of interior isolation devices 36 and the series of isolated wellbore sections 35 formed therebetween will preferably extend along the entire length of the predicted interaction zone 34 or beyond but can alternatively extend along just a portion or at least most of the predicted interaction zone 34. The number of the isolated wellbore sections 35 in the indirectly fractured wellbore section 18 can be less than, equal to, or greater than the number of the clusters of openings in the directly fractured wellbore interval 14—but will preferably be equal to the cluster spacing.

The longitudinal length of the isolated wellbore sections 35 in the second wellbore interval 18 can be the same or different. The longitudinal length of each isolated wellbore section 35 can be less than, equal to, or greater than the maximum cluster spacing distance in the first wellbore interval 14. However, the longitudinal length of each isolated wellbore section 35 (i) will preferably be less than or equal to the maximum cluster spacing distance and (ii) will more preferably be equal to the cluster spacing.

Using a series of interior isolation devices 36 spaced apart in this manner to divide the interaction zone 34 of the indirectly fractured wellbore interval 18 into a corresponding longitudinal series of isolated sections 35 beneficially operates to ensure that the fracturing fluid which reaches the indirectly fractured wellbore interval 18 will then produce a greater number of subsequent fractures which continue to propagate from the other side of the indirectly fractured wellbore interval 18. Without the presence of the series of isolation devices 36 and the isolated sections 35, the fracturing fluid that reaches the indirectly fractured wellbore interval 18 at all locations along the interacting zone 34 would be allowed to flow together in the undivided wellbore interval 18. The resulting combination of all of the fracturing fluid from all of the incoming fractures in the indirectly fractured wellbore interval 18 would typically result in the production of fewer fractures, and potentially even only a single fracture, which would continue to propagate from the other side of the indirectly fractured wellbore 18.

At least one of the isolation devices 36, or a different isolation device, will preferably be positioned cither at or just beyond the end of the interacting zone 34 of the indirectly fractured wellbore interval 18 which is closest to the wellhead assembly 4 which serves the wellbore interval 18. This isolates the upper end of interaction zone 34 to (i) prevent fracturing fluid from uselessly flowing up the well and (ii) prevent pressure loss. In addition, in the case where the direct and indirect wellbore intervals 14 and 18 are located in two different wells, this prevents the fracturing fluid which is pumped into the directly fractured wellbore interval 14 and received by the indirectly fractured wellbore interval 18 from flowing out of, and being recovered from, the wellhead of the second well.

In the inventive indirect fracturing procedure, a fracturing fluid will be pumped via the wellhead assembly 4 into the directly fractured wellbore interval 14, under pressure, to thereby produce the interacting fractures 24 which propagate toward and are received in the interacting zone 34 of the indirectly fractured wellbore interval 18. Initially, the fracturing fluid can optionally include sand or other proppant material but will preferably be a non-viscosified or viscosified fluid, or other fluid system such as, e.g., typically utilized in the particular reservoir in question to maximize fracture length. If sand or other proppant material is not initially included in the fracturing fluid, it will subsequently be added, preferably when sufficient geometry has been created in the formation 8 to enable proppant admittance.

To monitor the indirect fracturing procedure and detect when the fracturing fluid reaches and is received in the indirectly fractured wellbore interval 18, various types of sensors and tools can be used. For example, one or more pressure sensors can be placed in the indirectly fractured wellbore interval 18 to detect, in real time, pressure increases or decreases caused by the arrival or other actions of the fracturing fluid. As another example, microseismic imaging can be used to view what is happening in the indirectly fractured wellbore interval 18 in real time. As another example, temperature or hydrocarbon degradable fibers can be placed in proppant stages so that the fibers are picked up by the fracturing fluid and the arrival of the fibers in the indirectly fractured wellbore interval 18 will cause a decrease in temperature which is detected, in real time, by temperature sensors located in the wellbore interval 18. As another example, acoustic measurements of the incoming hydraulic fractures can be taken using distributed acoustic sensors and used to quantify the intersection of the hydraulic fractures. As another example, although not providing information in real time, tracers can be used to confirm the arrival of the fracturing fluid in the indirectly fractured wellbore interval 18. As another example, fiber measurements can be utilized to identify the incoming fractures and understand the impact of the plug spacing on the outgoing fractures.

When the fracturing fluid reaches the indirectly fractured wellbore interval 18, the pumping of the fracturing fluid into the directly fractured wellbore interval 14 will preferably be continued at a pressure sufficient to cause the fracturing fluid to flow out of the isolation sections 35 of the indirectly fractured wellbore interval 18, on the side of the wellbore interval 18 which generally faces away from the directly fractured wellbore interval 14, to propagate further fractures 38 in the subterranean formation 8 from and beyond the indirectly fractured wellbore interval 18.

To assist in forming and supporting the fractures 38 propagating from and beyond the indirectly fractured wellbore interval 18, plugs of sand or other proppant material can be placed in the isolated sections 35 of the indirectly fractured wellbore interval 18 using coiled tubing or other techniques. The sand or other proppant material placed in the isolated sections 35 of the indirectly fractured wellbore interval 18 will be picked up by the fracturing fluid to thereby replace the proppant which was removed from the now depleted fracturing fluid as it traveled from the first wellbore interval 14 to the second wellbore interval 18.

In another aspect of the inventive indirect fracturing procedure and system which is illustrated in FIG. 2, a new or existing third wellbore interval 40 can also be provided, for indirect fracturing, in the subterranean formation 8 adjacent to the downstream fracturing side of the second wellbore interval 18 (i.e., adjacent the side of the second wellbore interval 18 which is opposite the first wellbore interval 14). The third wellbore interval 40 can be an interval of a different well or can be a different interval of the same deviated, horizontal, horseshoe, or vertical well as the first wellbore interval 14 and/or the second wellbore interval 18. As illustrated in FIG. 2, the third wellbore interval 40 is positioned and oriented with respect to the second wellbore interval 18 so that at least some of the hydraulic fractures 38 propagated from and beyond the second wellbore interval 18 propagate toward and at least reach the third wellbore interval 40. The hydraulic fractures 38 from the second wellbore interval 18 which reach the third wellbore interval 40 are referred to herein as secondary interacting hydraulic fractures.

In every respect, the third wellbore interval 40 can and will preferably be located, prepared, and configured for indirect fracturing downstream of the second wellbore interval 18 in the same manner, as described above, that the second wellbore interval 18 was located, prepared, and configured for indirect fracturing downstream of the directly fractured wellbore interval 14. Prior to the propagation of hydraulic fractures 38 from and beyond the second wellbore interval 18, one or more longitudinal sections 42 of a predicted interaction zone 44 of the third wellbore interval 40 (i.e., the zone 44 in which it is predicted that the secondary interacting hydraulic fractures 38 from the second wellbore interval 18 will interact with the third wellbore interval 40) will preferably be isolated by positioning a series of two or more hard plugs or other isolation devices 46 in the third wellbore interval 40.

As with the second wellbore interval 18, at least one of the isolation devices 46, or a different isolation device, will preferably be positioned cither at or just beyond the end of the interacting zone 44 of the third wellbore interval 40 which is closest to the wellhead assembly which serves the third wellbore interval 40. This isolates the upper end of interaction zone 44 to (i) prevent fracturing fluid from uselessly flowing up the well and (ii) prevent pressure loss. In addition, in the case where the third wellbore interval 40 is located in a different well, this prevents the fracturing fluid which is pumped into the directly fractured wellbore interval 14 and received by the third wellbore interval 40 via the second wellbore interval 18 from flowing out of, and being recovered from, the wellhead assembly associated with the third wellbore interval 40.

The third wellbore interval 40 can also be monitored in any manner as described above for the second wellbore interval 18 to detect the arrival of the fracturing fluid in the interacting zone 44 of the third wellbore interval 40. When the fracturing fluid reaches the indirectly fractured third wellbore interval 40, the pumping of the fracturing fluid into the directly fractured wellbore interval 14 will preferably be continued at a pressure sufficient to cause the fracturing fluid to flow out of the isolation sections 42 of the third wellbore interval 40, on the side of the wellbore interval 40 facing away from the second wellbore interval 18, to propagate further fractures 48 in the subterranean formation 8 from and beyond the indirectly fractured third wellbore interval 40.

It will also be understood that the inventive indirect fracturing procedure and system can be used to indirectly fracture a fourth or any number of additional wellbore intervals which are within range of the indirect fracturing capability of the fracturing system which is used for directly fracturing the first wellbore interval 14. In addition, depending on the orientation of the fracturing planes or other geological characteristics of the subterranean formation 8, a plane of symmetry in which the two, three, or more wellbore intervals 14, 18, 40 are located can be horizontal or vertical or oriented at any other angle. Further, it will be understood that different or the same portions of any of the indirectly or directly fractured wellbore intervals can be directly fractured or directly refractured to further stimulate the wellbore interval in question and/or to indirectly stimulate or indirectly restimulate one or more adjacent wellbore intervals. It will also be understood that a directly fractured wellbore interval can be used to indirectly, and simultaneously if desired, fracture wellbore intervals which are on opposite sides of the directly fractured wellbore interval or at other locations.

Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those in the art. Such changes and modifications are encompassed within the invention as defined by the claims.