Method of drilling lateral wellbores from a slant well without utilizing a whipstock

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to systems and methods for the recovery of subterranean resources and, more particularly, to a method of drilling lateral wellbores from a slant well without utilizing a whipstock.

BACKGROUND OF THE INVENTION

Subterranean deposits of coal (typically referred to as “coal seams”) often contain substantial quantities of entrained methane gas. Limited production and use of methane gas from coal seams has occurred for many years because substantial obstacles have frustrated extensive development and use of methane gas deposits in coal seams.

One system of obtaining methane gas from coal seams is to drill lateral wellbores into the coal seams. This is typically accomplished by a drill bit at the end of a drill string that is disposed within a casing string having a deflecting member at the lower end thereof. The deflecting member, sometimes referred to as a “whipstock,” directs the drill bit such that a lateral wellbore may be drilled in the coal seam.

SUMMARY OF THE INVENTION

The present invention provides a wellbore sealing system and method that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods.

In accordance with one embodiment of the present invention, a method for drilling a lateral wellbore from a slant well includes drilling the slant well below the surface of the earth such that the slant well is angled toward a first horizontal direction that coincides with a desired drilling direction for the lateral wellbore. The slant well has a borehole wall that includes a high side portion closest to the surface, a low side portion farthest from the surface, and two side portions between the high side portion and the low side portion. The method further includes disposing a casing string in the slant well, disposing a drill string having a bent sub, a mud motor, and a drill bit coupled at a lower end thereof in the casing string, and positioning the drill bit adjacent either one of the side portions or the low side portion. The method further includes drilling, from either the side portion or the low side portion, an intermediate wellbore with the drill bit, and drilling, from the intermediate wellbore, the lateral wellbore in the desired drilling direction.

Some embodiments of the present invention may provide one or more technical advantages. These technical advantages may include more efficient drilling and production of methane gas and greater reduction in costs and problems associated with other drilling systems and methods. For example, a whipstock does not have to be used to direct a drill bit to drill a lateral wellbore. Another technical advantage is that underbalanced drilling may be performed along with the teachings of one embodiment of the present invention.

Other technical advantages of the present invention are readily apparent to one skilled in the art from the figures, descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like numerals represent like parts, in which:

FIG. 1 is a cross-sectional view of the earth illustrating an example slant well system for production of resources from one or more subterranean zones via one or more lateral wellbores;

FIG. 2 is a three-dimensional perspective view illustrating how a lateral wellbore is drilled from a slant well according to one embodiment of the present invention;

FIGS. 3A and 3B are different cross-sectional views of the perspective view of FIG. 2; and

FIG. 4 is a flowchart demonstrating an example method for drilling lateral wellbores from a slant well according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention and their advantages are best understood by referring now to FIGS. 1 through 4 of the drawings, in which like numerals refer to like parts.

FIG. 1 is a cross-sectional view of the earth illustrating an example well system 100 for production of resources from one or more subterranean zones 102 via one or more lateral wellbores 104. In various embodiments described herein, subterranean zones 102 are coal seams; however, other subterranean formations may be similarly accessed using well system 100 of the present invention to remove and/or produce water, gas, or other fluids. System 100 may also be used for other suitable operations, such as to treat minerals in subterranean zone 102 prior to mining operations, or to inject or introduce fluids, gasses, or other substances into subterranean zone 102.

Referring to FIG. 1, well system 100 includes an entry wellbore 105, slant wells 106, a plurality of lateral wellbores 104, and a cavity 108 associated with each slant well 106. Entry wellbore 105 extends from a surface 12 towards subterranean zones 102. Entry wellbore 105 is illustrated in FIG. 1 as being substantially vertical; however, entry wellbore 105 may be formed at any suitable angle relative to surface 12 to accommodate, for example, surface 12 geometries and/or subterranean zone 102 geometries.

Slant wells 106 extend from the terminus of entry wellbore 105 toward subterranean zones 102, although slant wells may alternatively extend from any other suitable portion of entry wellbore 105 or from surface 12. Where there are multiple subterranean zones 102 at varying depths, as illustrated in FIG. 1, slant wells 106 extend through the subterranean zones 102 closest to surface 12 into and through the deepest subterranean zones 102. There may be one or any number of slant wells 106.

As illustrated, if slant wells 106 are formed from an entry wellbore 105, then they may extend away from entry wellbore 105 at an angle designated α, which may be any suitable angle to accommodate surface topologies and other factors similar to those affecting entry wellbore 105. If multiple slant wells 106 are formed, as illustrated, then they may be spaced in relation to each other at an angular separation of β degrees, which may be any suitable angle, such as 60 degrees. However, slant wells 106 may be separated by other angles depending likewise on the topology and geography of the area and location of a targeted subterranean zone 102. As described in further detail below, each slant well 106 is angled toward a horizontal direction that coincides with the drilling direction for at least one lateral wellbore 104. Slant wells 106 may also include cavity 108 located at a terminus of each slant well 106 to collect fluids from subterranean zones 102.

Lateral wellbores 104 extend from each slant well 106 into an associated subterranean zone 102. Lateral wellbores 104 are shown in FIG. 1 to be substantially horizontal; however, lateral wellbores 104 may be formed in other suitable directions off of slant wells 106 and may have a curvature associated therewith. Any suitable systems and/or methods may be used to drill lateral wellbores 104; however, a particular method for drilling lateral wellbores 104 according to one embodiment of the present invention is described below in conjunction with FIGS. 2 through 3B.

FIG. 2 is a three-dimensional perspective view illustrating the drilling of lateral wellbore 104 from slant well 106 according to one embodiment of the present invention. According to the teachings of one embodiment of the present invention, lateral wellbore 104 is drilled from slant well 106 without utilizing a whipstock by first drilling an intermediate wellbore in a direction that is different from a desired drilling direction 203 of lateral wellbore 104. The drilling of intermediate wellbore 200 is described in further detail below.

FIGS. 3A and 3B are various cross-sectional views of the perspective view of FIG. 2. Referring to FIGS. 2, 3A and 3B, slant well 106 is shown to be drilled at an angle toward a first horizontal direction 202 that coincides with desired drilling direction 203 of lateral wellbore 104. Note that the arrow representing first horizontal direction 202 in FIG. 3A is coming out of the page. Slant well 106 may be drilled using any suitable drilling methods.

To drill lateral wellbore 104, a casing string 300 may be first disposed in slant well 106, as shown best in FIG. 3A. A drill string 302 may then be disposed in casing string 300, also shown in FIG. 3A. In the illustrated embodiment, drill string 302 includes a bent sub 306 at a lower end thereof, a mud motor (not explicitly shown), and a drill bit 304. In previous methods of drilling lateral wellbores, the casing string that is disposed in a slant well has a whipstock at a lower end thereof to direct the drill bit laterally so that a lateral wellbore 204 may be drilled. This is illustrated in FIG. 2, in which lateral wellbore 204 is illustrated in hidden lines. Lateral wellbore 204 is drilled in the same direction as desired drilling direction 203 for lateral wellbore 104, except that the drilling of lateral wellbore 204 is with the use of the whipstock, whereas the drilling of wellbore 104, according to the teachings of the present invention, is utilized without a whipstock.

Lateral wellbore 204 is typically not able to be drilled without a whipstock because drill bit 304 is not able to penetrate a borehole wall 107 of slant well 106 near a point 205 on a high side portion 321 (FIG. 3B) of slant well 106, as shown in FIGS. 2 and 3B. This is because drill bit 304 is working against gravity and, when trying to penetrate borehole wall 107 of slant well 106 near point 205, drill bit 304 may deflect off borehole wall 107 because there is not enough force to penetrate or “bite into” borehole wall 107. This is one reason that intermediate wellbore 200 is drilled to create lateral wellbore 104 without the use of a whipstock, as described in further detail below. The deflecting of a drill bit off of a borehole wall is not a problem when utilizing a whipstock because a whipstock is configured in such a manner that it not only directs a drill bit toward a desired drilling direction but forces the drill bit to penetrate or “bite into” a wall of a borehole in spite of any gravity that may be encountered.

To avoid having to work against gravity and to be able to penetrate borehole wall 107 of slant well 106 without using a whipstock, drill bit 304 is initially positioned at a drill point on borehole wall 107 such that penetration of borehole wall 107 may be achieved. Intermediate wellbore 200 may then be drilled in a direction 207, as best illustrated in FIG. 3A. In the illustrated embodiment, intermediate wellbore 200 is essentially drilled from a “side portion” of slant well 106, in which direction 207 is at an angle of approximately ninety degrees offset from desired drilling direction 203 of lateral wellbore 104 in a generally horizontal plane. This is most clearly illustrated in FIG. 3B. Any suitable angle may be formed between desired drilling direction 203 and direction 207, as long as drill bit 304 is able to penetrate borehole wall 107 of slant well 106 without the use of a whipstock.

Referring to FIG. 3B, a horizontal cross-section of slant well 106 illustrates borehole wall 107 being divided into four approximately equal portions, as denoted by lines 320 in FIG. 3B. The four portions include high side portion 321 that is closest to surface 12, a low side portion 323 that is farthest from surface 12, and two side portions 322 disposed between high side portion 321 and low side portion 323. In one embodiment, drill bit 304 is positioned at a drilling point on borehole wall 107 of slant well 106 such that the drill point is within either side portions 322 or low side portion 323. Thereafter, drill bit 304 is used to drill intermediate wellbore 200 from that drill point before making a turn toward desired drilling direction 203 to drill lateral wellbore 104. Intermediate wellbore 200 includes any turns that may be formed before drilling lateral wellbore 104. As shown in FIG. 3B, the drill point is located in a side portion 322; however, other suitable drill points may be utilized. For example, the drilling point may be located at low side portion 323. If so, then intermediate wellbore 200 may first turn toward side portion 322 before turning toward desired drilling direction 203.

Under-balanced drilling may also be performed using the teachings of the present invention. As such, an inner annulus 310 is formed between the inner surface of casing string 300 and the outer surface of drill string 302, and an outer annulus 308 is formed between an outside surface of casing string 300 and the wall of slant well 106. Inner annulus 310, outer annulus 308, and drill string 302 may be used to perform under-balanced drilling. As one example, a first fluid may be circulated down drill string 201, such as drilling mud or other suitable drilling fluids, and a second fluid is circulated down inner annulus 310, such as air, nitrogen, or other relatively light fluid. Both first and second fluids then mix and flow up outer annulus 308. The purpose of the second fluid is to lighten the weight of the first fluid such that the hydrostatic head of the first fluid does not force the first fluid into the subterranean formation. As a variation, the second fluid may be circulated down outer annulus 308 and the mixture of the first and second fluids may flow up inner annulus 310.

In operation of the embodiment of the system shown in FIGS. 2 through 3B, slant well 106 is drilled using a suitable drilling method. Casing string 300 is inserted into slant well 106 and drill string 302 is then inserted within casing string 300. Once at a desired depth, drill bit 304 is then positioned at a drill point on the wall of slant well 106 so that intermediate wellbore 200 may be drilled. Since a whipstock is not included in casing string 300, there is no deflecting member to direct drill bit 304 in desired drilling direction 203. Therefore, to be able to penetrate borehole wall 107 of slant well 106, drill bit 304 is positioned at a drill point on borehole wall 107 so that penetration may be achieved. In one embodiment, the drill point is positioned against a side portion 322 of borehole wall 107. Intermediate wellbore 200 is then drilled using drill bit 304. This includes directing drill bit 304 such that drill bit 304 is oriented toward desired drilling direction 203. When drill bit 304 is oriented in desired drilling direction 203, then drill bit 304 is used to drill lateral wellbore 104, as most clearly shown in FIG. 3B.

FIG. 4 is a flow chart demonstrating an example method for drilling lateral wellbores 104 from slant well 106 according to one embodiment of the present invention.

The method begins at step 400 where slant well 106 is drilled below surface 12 of the earth. Slant well 106 is angled toward first horizontal direction 202 that coincides with desired drilling direction 203 for lateral wellbore 104. Casing string 300 is disposed in slant well 106 in step 402, and drill string 302 is disposed in casing string 300 at step 404. Drill string 302 has bent sub 306, a mud motor, and drill bit 304 coupled at a lower end thereof. Once drill bit 304 is at a desired depth, drill bit 304 is positioned adjacent to one of two side portions 322 (or low side portion 323) of borehole wall 107 at step 406. Then intermediate wellbore 200 is drilled from side portion 322 (or low side portion 323) at step 408 with drill bit 304. At step 410, lateral wellbore 104 is drilled in desired drilling direction 203 from intermediate wellbore 200. Drilling intermediate wellbore 200 before drilling lateral wellbore 104 facilitates the drilling of lateral wellbore 104 without having to utilize a whipstock at the end of casing string 300. Intermediate wellbore 200 is drilled in a direction that is different from the desired drilling direction 203 so that drill bit 304 may penetrate borehole wall 107 of slant wall 106. This is because drill bit 304 cannot penetrate borehole wall 107 when working against the force of gravity in this direction and, therefore, intermediate wellbore 200 must be drilled from either side portion 322 or low side portion 323 before drilling lateral wellbore 104 in desired drilling direction 203. This ends the method as outlined in FIG. 4.

Although the present invention is described with several embodiments, various changes and modifications may be suggested to one skilled in the art. The present invention intends to encompass such changes and modifications as they fall within the scope of the appended claims.