PRODUCING DISCONNECTED PROPPED FRACTURES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present document is based on and claims priority to US Provisional

Application Serial No.: 62/635,876, filed February 27, 2018, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] In various well applications, the subterranean formation is stimulated to enhance recovery of hydrocarbon fluids such as oil and gas. One form of well stimulation is hydraulic fracturing which may be conducted in a wellbore following a drilling operation and an optional casing operation. Hydraulic fracturing operations initially were performed in single stage vertical or near vertical wells. To further improve productivity, however, hydraulic fracturing operations have trended toward use in generally horizontal wells. Although horizontal fracturing operations have improved productivity, current methods have limitations with respect to productivity and efficiency in certain types of subterranean environments and operations. Additionally, the total surface area of a propped fracture may not remain connected to the original borehole due to, for example, the presence of geological pinch points. SUMMARY

[0003] In general, the present disclosure provides a methodology and system for enhancing hydrocarbon fluid production. According to an embodiment, a primary borehole is oriented through a stimulation zone, and a secondary borehole is disposed through the stimulation zone at an angle with respect to the primary borehole. At least one tunnel, e.g. a plurality of tunnels, may be routed laterally from the secondary borehole and may extend at least partially within the stimulation zone. The arrangement can promote fluid conductivity through a potentially greater portion of the stimulation zone when the stimulation zone is fractured.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Certain embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate various

implementations described herein and are not meant to limit the scope of various technologies described herein, and:

[0005] Figure l is a schematic illustration of an example of a well system having a primary borehole extending through a stimulation zone, according to an embodiment of the disclosure;

[0006] Figure 2 is a schematic illustration showing an example of a stimulation zone with a pinch point barrier restricting flow along a fracture or fractures in the stimulation zone, according to an embodiment of the disclosure;

[0007] Figure 3 is a schematic illustration of an example of a well system having a secondary borehole and corresponding tunnels combined with the primary borehole to facilitate fluid conductivity, according to an embodiment of the disclosure; and [0008] Figure 4 is a schematic illustration showing an example of a stimulation zone with a pinch point barrier but with enhanced fluid conductivity via the secondary borehole and corresponding tunnels, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0009] In the following description, numerous details are set forth to provide an understanding of some illustrative embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or

methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.

[0010] The disclosure herein generally relates to a methodology and system for enhancing hydrocarbon fluid production. According to an embodiment, a primary borehole is oriented through a stimulation zone, and a secondary borehole is disposed through the stimulation zone at an angle with respect to the primary borehole. In some embodiments, the primary borehole and secondary borehole are generally perpendicular to each other although the primary borehole and secondary borehole may be arranged at various other angles with respect to each other. In some embodiments, the primary borehole and secondary borehole do not intersect each other but each extends through the stimulation zone (partially or fully through the stimulation zone).

[0011] At least one tunnel may be routed laterally from the secondary borehole and may extend at least partially within the stimulation zone. As used herein, the term “laterally” is intended to indicate a direction which is different from the direction of the corresponding borehole. In various applications, a plurality of tunnels, e.g. two tunnels, may extend laterally from the secondary borehole. In some embodiments, the primary borehole may be a deviated borehole, e.g. a generally horizontal borehole; the secondary borehole may be generally vertical; and the tunnel(s) may be oriented generally horizontally. However, various other arrangements and orientations of the primary borehole, secondary borehole, and tunnels may be utilized depending on, for example, the characteristics of the formation in which the stimulation zone resides. The arrangement is configured to promote fluid conductivity through a potentially greater portion of the stimulation zone upon fracturing of the stimulation zone. It should be noted the primary borehole may be a deviated portion of a wellbore drilled from the surface and then turned laterally and drilled to form a deviated borehole in the subterranean region/formation containing the stimulation zone.

[0012] The stimulation zone may be subjected to a stimulation treatment to facilitate production of oil and/or other hydrocarbons. For example, the stimulation zone may be subjected to a hydraulic fracturing operation to create large propped fractures that provide high conductivity via high surface area conduits formed through or proximate the stimulation zone. The high surface area conduits facilitate flow of fluid from a reservoir contained in the formation to a primary borehole, e.g. a deviated borehole. However, the total surface area of the propped fractures does not always remain connected to the primary borehole due to the presence of, for example, geological pinch points. The geological pinch points may comprise vertical pinch points which isolate portions of a fracture or fractures from the primary borehole and thus prevent the entire network of fractures from conducting hydrocarbon fluids to the primary borehole.

[0013] Referring generally to Figure 1, an embodiment of a well system 20 is illustrated as extending into a subterranean region 22, e.g. a formation. The well system 20 enables a methodology for enhancing recovery of hydrocarbon fluid, e.g. oil and/or gas, from a well. In this embodiment, the well system 20 comprises a primary borehole 24, e.g. a primary wellbore, drilled down into the subterranean region 22. By way of example, the primary borehole 24 may be a deviated portion of a wellbore drilled from the surface and then turned laterally and drilled to form a deviated borehole, e.g.

horizontal borehole, in the subterranean region/formation 22.

[0014] In the example illustrated, the primary borehole 24 is disposed through a stimulation zone 26 located in the subterranean region/formation 22. In some

embodiments, the stimulation zone 26 may comprise a plurality of fracture zones or production zones 28 resulting from, for example, a multistage hydraulic fracturing job. The fracture zones 28 may comprise a network of fractures 30 which are propped open with a suitable proppant delivered during the hydraulic fracturing job. However, the stimulation zone 26 may be stimulated in a variety of ways other than (or in addition to) hydraulic fracturing to increase production from primary borehole 24. For example, stimulation zone 26 may be stimulated via various stimulation treatments including acid injection, acid fracturing, and/or hydraulic fracturing.

[0015] With additional reference to Figure 2, the total surface area of the propped fracture(s) 30 sometimes fails to remain fluidly connected to the primary borehole 24, e.g. horizontal wellbore section, due to the presence of a geological pinch point or points 32. The pinch point or pinch points 32 can isolate a fracture region 34 from the primary borehole 24 which reduces the fluid conductivity of the stimulation zone 26 and thus limits production of well fluid. Effectively, the pinch point(s) 32 separates the isolated fracture region 34 of stimulation zone 26 from a non-isolated fracture region 35 of stimulation zone 26 which surrounds the primary borehole 24. In some embodiments, the pinch points 32 are in the form of vertical pinch points which isolate fracture region 34 from non-isolated fracture region 35 and thus from primary borehole 24. The isolation of portions of the stimulation zone 26 prevents the entire network of fractures 30 from conducting hydrocarbon fluid to the primary borehole 24. The isolated fracture region 34 may comprise, for example, an ash bed layer, a clay-rich formation layer that can be destabilized by water, or other types of regions, as will be appreciated by those skilled in the art.

[0016] However, a secondary borehole 36 is formed at an angle with respect to the primary borehole 24 and may also be positioned to enter the stimulation zone 26 as illustrated in Figure 3. For example, the secondary borehole 36 may extend through (partially or fully) the stimulation zone 26. However, the secondary borehole 36 may be positioned outside and/or proximate the stimulation zone 26 in various applications. In some embodiments, the secondary borehole 36 may not intersect the primary borehole 24. For example, the secondary borehole 36 may be drilled in the vicinity of the primary borehole 24, e.g. within a portion of the length of propped fractures 30. According to one embodiment, the secondary borehole 36 may be drilled within a half length of the propped fractures 30. In some embodiments, the secondary borehole 36 is generally vertical but it may have a variety of orientations and angles with respect to the primary borehole 24. As further illustrated in Figure 4, the secondary borehole 36 may be oriented to extend through the geological pinch point(s) 32 to provide a fluid conduit from the isolated fracture region 34 of stimulation zone 26 to the non-isolated portion 35 of stimulation zone 26 which surrounds the primary borehole 24.

[0017] At least one tunnel 38 may be formed to extend from the secondary borehole 36 and is positioned at least partially in the stimulation zone 26. For example, a plurality of tunnels 38, e.g. two tunnels, may be formed to extend from the secondary borehole 36 while being positioned at least partially in stimulation zone 26. Tunnel 38 or a plurality of tunnels 38 may be positioned at a variety of angles in relation to the primary borehole 24 and secondary borehole 36. The tunnel(s) 38 may be milled, jetted, or otherwise formed to extend from the secondary borehole 36 so as to extend through at least a portion of the isolated fracture region 34. In this manner, the tunnel(s) 38 increase connectivity with a portion or portions of the propped fractures 30 that are isolated from the primary borehole 24 via the pinch point(s) 32. The tunnels 38 enable conveyance of, for example, hydrocarbon fluids from the isolated fracture region 34 to the secondary borehole 36, and then on to the non-isolated region 35 and primary borehole 24 in spite of the pinch points 32, as illustrated in Figures 3 and 4. In some embodiments, further stimulation operations, e.g. hydraulic fracturing, acid fracturing, and/or acid injection may be performed through one or more tunnels 38 to facilitate production of well fluids. However, production operations may be conducted without performing stimulation operations through the tunnel or tunnels 38.

[0018] As illustrated, the secondary borehole 36 may serve as a conduit for fluid flowing along tunnels 38 to cross over pinch point barrier 32 and into the region 35 of stimulation zone 26 readily able to conduct fluid to primary borehole 24. The tunnels 38, in cooperation with secondary borehole 36, also may be used to promote fluid conductivity between disconnected parts of fractures 30 in the stimulation zone 26. For example, the system may be used to facilitate flow from unpropped portions of the fracture system which may still be fluidly conductive and/or to facilitate flow along fractures created using, for example, acid frac methodologies.

[0019] However, the construction, configuration, and operation of well system 20 may vary depending on the parameters of the subterranean region 22 and of the hydrocarbon fluid to be produced. In some embodiments, the tunnels 38 may be created, e.g. drilled, and allowed to conduct fluid received from the stimulation zone 26, such as from the network of fractures 30. In some embodiments, the tunnels 38 may be created and stimulated to enhance the connection between tunnels 38 and, for example, pre- existing propped fractures. Additionally, multiple tunnels 38, e.g. multiple pairs of tunnels, may be formed to extend from the secondary borehole 36 to engage multiple layers of formation 22 isolated from the primary borehole 24 by separate pinch points 32. The pairs of tunnels 38 facilitate conveyance and/or production of hydrocarbon fluid flow from the stimulation zone 26, towards the secondary borehole 36, and, optionally, on to the primary borehole 24.

[0020] With respect to construction of well system 20, the primary borehole 24 may be a horizontal borehole formed and stimulated prior to drilling of the secondary borehole (or boreholes) 36 which may be vertically oriented. However, the primary borehole 24 also may be formed and/or stimulated after drilling of the secondary borehole 36. Additionally, the tunnel or tunnels 38 may be created prior to creating and/or prior to stimulating the primary borehole 24.

[0021] Furthermore, the time period between the stimulation treatment of the primary borehole 24 (primary well) and the creation of tunnels 38 on the secondary bore(s) 36 can vary. In some applications, the time period may be relatively short and the stimulation treatment and tunnel formation can be done nearly simultaneously. However, the time period can vary substantially, e.g. zero days to 100 years. In some applications, for example, the primary borehole 24 may be obtained via an abandoned horizontal well which may be plugged using hardware tools, cement, or other isolating techniques. The secondary borehole(s) 36, e.g. vertical wells, can be drilled at a specific location or locations selected to enhance well productivity. In some applications, existing wells can be used for the secondary boreholes 36.

[0022] Depending on parameters of a given application, the secondary borehole or boreholes 36 may be generally vertical or deviated. In a variety of embodiments, the secondary borehole(s) 36 are arranged generally vertically through the production zones 28, e.g. where the fractures 30 extending from the primary borehole 24 are located and where the tunnels 38 are to be located. With respect to the tunnels 38, the tunnels 38 may be created using various methods including drilling, milling, jetting, abrasive jetting, electrical treatment, laser treatment, or other suitable techniques. In some embodiments, the tunnels 38 may be created at a generally 90° angle with respect to the direction of the secondary borehole 36. However, the tunnels 38 also may be formed at other suitable angles with respect to the secondary borehole 36 to facilitate, for example, enhanced productivity.

[0023] Also, in some embodiments the tunnel 38 or plurality of tunnels 38 may have a complex geometry such that the tunnel(s) 38 may extend from the secondary borehole 36 at a selected deviation angle and then such deviation angle may gradually change. For example, the deviation angle between the secondary borehole 36 and at least one of the tunnels 38 may gradually change from 0° to 90° (or other suitable angle) during propagation of the tunnel 38 into the stimulation zone 26. In other embodiments, the deviation angle between at least one of the tunnels 38 and the secondary borehole 36 may remain the same along the entire length of the tunnel 38. For example, at least one of the tunnels 38 may be created and propagated at a 90° angle relative to the secondary borehole 36.

[0024] Additionally, the tunnels 38 may be formed to penetrate through several formation layers or to stay within one formation layer. Depending on parameters of a given application, the tunnels 38 may be open hole, completed with casing, completed with perforated or slotted liners, and/or completed with filters. The tunnels 38 may have uniform orientations or they may be positioned chaotically, e.g. in a variety of different orientations. In various applications, the tunnels 38 are oriented in a direction of minimum horizontal in situ stress and/or in a direction of maximum horizontal in situ stress and/or in a common horizontal direction with the secondary borehole 36. The number of tunnels 38 can vary substantially, e.g. 1 to 10,000 tunnels. The lengths of the tunnels 38 can vary from, for example, 5 feet to 10,000 feet. In some embodiments, the lengths of the tunnels vary from 10 feet to 1000 feet and in some applications the tunnels vary from 30 feet to 500 feet, as disclosed in US Patent Application Publication No. 2018/0023375, the entirety of which is incorporated by reference herein.

[0025] In some embodiments, the secondary borehole or boreholes 36 and/or primary borehole 24 may be completed with completion(s) 40 enabling control over production from various groups of tunnels 38 (see Figure 3). For example, a given completion 40 may be constructed to enable production from specific groups of tunnels 38 and from specific secondary boreholes 36. In this manner, production from different groups of tunnels 38 may be done collectively, separately, and/or at various rates. The tunnels 38 also may be used for different functions, e.g. production and injection. For example, some of the tunnels 38 may be used for producing hydrocarbons and some of the tunnels 38 may be used for injecting various fluids into the formation 22, e.g. into the network of fractures 30 extending from the primary borehole 24.

[0026] In one type of operational embodiment, hydrocarbon fluids flow along fractures 30, located in isolated fracture region 34, until entering tunnels 38. The hydrocarbon fluids are then able to flow along tunnels 38 until entering secondary borehole 36. The secondary borehole(s) 36 is oriented to extend through the one or more geological pinch points 32 so as to provide a flow conduit from the isolated fracture region 34 to the non-isolated fracture region 35 of stimulation zone 26 which surrounds the primary borehole 24. The hydrocarbon fluids flow along the secondary borehole(s) 36 and into the non-isolated fracture region 35 from which they are then able to migrate to the primary borehole 24 via the fractures 30 extending from the primary borehole 24. By orienting the secondary borehole 36 through the geological pinch point or points 32, otherwise isolated portions of the stimulation zone 26 are provided with a flow path to primary borehole 24. The resulting fluid conductivity through a greater portion of the stimulation zone 26, upon fracturing of the stimulation zone 26, ensures enhanced recovery of the hydrocarbon fluids located in the overall stimulation zone 26.

[0027] The well system 20, e.g. primary borehole 24, may be stimulated using propped hydraulic fracturing, acid fracturing, propellant fracturing, or other stimulation techniques based on creating pressure in at least a portion of the reservoir above the level of the fracturing pressure of the given formation 22. The primary borehole 24 also may be completed with various types of completion equipment. The completion techniques may comprise casing and completing the borehole, using an open hole completion, using a multi-stage fracturing completion, and/or using other types of completion equipment. Additionally, the stimulation treatment, e.g. hydraulic fracturing job, may be performed on at least a portion of the primary borehole 24 a period of time before, e.g. more than one year before, the formation of the first tunnel 38. In some applications, the primary borehole 24 may even have been abandoned before formation of the first tunnel 38 from secondary borehole 36. Also, the secondary borehole 36 may be created before or after the primary borehole 24.

[0028] Furthermore, desired stimulation operations may be performed at various times. For example, the stimulation zone 26 may be stimulated prior to creation of the tunnel or tunnels 38 and may be stimulated using, for example, acid injection, acid fracturing, and/or hydraulic fracturing. In some embodiments, the tunnels 38 also may be stimulated using such techniques, although other applications may omit stimulation of the tunnels 38. In some applications, formation of the primary borehole 24 and/or stimulation of the stimulation zone 26 around primary borehole 24 may be performed substantially before creation of the tunnels 38. However, other applications may perform stimulation operations of the tunnels 38 and/or secondary borehole 36 at times proximate the formation of primary borehole 24 or at other suitable times depending on the approach employed for recovery of well fluids. [0029] Although a few embodiments of the system and methodology have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.