Wellbore completion design to naturally separate water and solids from oil and gas

A wellbore completion design is provided, which creates a convective flow action that separates water and sand from hydrocarbons during production of the hydrocarbons from a subterranean formation. A deviated section of the wellbore creates the desired effect. The wellbore completion design may include a secondary bore, which intersects the deviated section of the wellbore at an acute angle, to accumulate the separated water and sand. An injection pump disposed in the toe section of the secondary bore can also be employed to pump the water back into the water containing portion of the subterranean formation. If solids are present in more than trace amounts, the toe section of the secondary bore may be formed at an acute angle to the remaining portion of the secondary bore to prevent blockage of the pump. Alternatively, a tertiary bore may be provided, so that the solids can accumulate in the secondary bore and the water can flow into the tertiary bore.

BACKGROUND

The present invention is directed generally to methods of separating water and solids from oil and gas and more particularly to a wellbore completion design that separates water and solids from oil and gas downhole in such a way that the water and solids remain downhole. These solids will usually consist of granular to very fine sized formation solids, or solids introduced into the well during drilling, completion, stimulation, or production operations.

One of the most burdensome aspects of producing hydrocarbons from a well for well operators is dealing with the presence of solids and water in the hydrocarbons. It is not desirous to have either of these by-products present in the hydrocarbons. Indeed, the presence of these elements in hydrocarbons only inhibits their recovery, often to the degree that economics will force an operator to suspend or even abandon well production. Accordingly, well operators have had to develop techniques for removing or separating the sand and water from the hydrocarbons as nature itself in most wells lends no assistance in this regard. Many of the techniques developed to deal with the removal of these elements, however, are cumbersome, expensive, not always environmentally friendly and often involve complex processes and equipment.

One conventional technique for removing sand from the hydrocarbons is to install sand screens at the end of the production pipe or inside the wellbore through the producing interval. These sand screens typically comprise multiple layers of wire mesh. The pore sizes of these screens are usually selected to filter out or remove as many granules of sand present in a particular formation as possible. Thus, the screens can be, and often are, customized for a particular application. Thus, one screen does not usually “fit all.” Accordingly, well operators are required to learn as much about the nature of the formations they will be producing from to insure that they select the right sand screen to filter out as much of the sand as possible.

There are two major drawbacks to using sand screens for removing sand from hydrocarbons. First, over time the sand screens begin to plug up. This causes a decrease in the amount of hydrocarbons being produced. Eventually, the sand screens plug up entirely, requiring either removal of the sand screen or invocation of an operation to clean the sand screens, downhole. Typically, either operations will require the well to be shut down, which in turn ceases the production of hydrocarbons, and causes an additional economic loss to the well owner. Another major drawback of using sand screens attached to the production tubing is that eventually sand bridges form between the sand screen and the wellbore wall. These sand bridges block the flow of remedial treatment fluids, which occasionally need to be pumped downhole through the annulus between the production tubing and the wellbore. To unblock the sand bridges, the well often has to be shut down so that the sand screen can be removed for cleaning. This again results in an economic loss to the well owner.

Another technique for removing sand and other debris from the hydrocarbons being produced from a well is to employ a device at the surface, known as a separator; in some cases, specifically a sand separator. This technique involves producing the sand with the hydrocarbons. A drawback of this approach, however, is that the separator devices take up space at the surface, which is often limited in off-shore applications. Furthermore, it reduces the producing rate of the well, requires repeated cleaning or maintenance, and may be a separate additional device needed additional to a water separator system.

Water is usually removed from the hydrocarbons at the surface using multi-phase separation devices. These devices operate to agglomerate and coalesce the hydrocarbons, thereby separating them from the water. A drawback of this approach, however, is that no separation process is perfect. As such, some amount of the hydrocarbons always remains in the water. This can create environmental problems when disposing of the water, especially in off-shore applications. Also, the multi-phase separation devices are fairly large in size, which is another disadvantage in off-shore applications, as space is limited as pointed out above. Another limitation is that this can require additional maintenance or repair if solids are part of the produced fluid stream.

SUMMARY

The present invention is directed to a wellbore configuration that separates water and solids from oil and gas downhole in such a way that the water and solids remain downhole.

In one embodiment, the present invention is directed to a method of separating other fluids and solids from hydrocarbons being produced from a subterranean formation. The method comprises the step of forming a primary wellbore having a deviated section in the subterranean formation, which stimulates convective separation of the other fluids and solids from the hydrocarbons during production of the hydrocarbons from the subterranean formation. The method may include the additional step of forming a secondary bore, which intersects the deviated section of the primary wellbore at an acute angle into which is accumulated one or more of the other fluids and solids separated from the hydrocarbons. The present invention may further comprise the step of drilling a tertiary bore, which intersects the secondary bore at an acute angle such that the solids accumulate in the secondary bore and the fluids accumulate in the tertiary bore. In yet another aspect of the present invention, perforations and/or fractures may be formed in either the secondary bore or the tertiary bore and a pump may be employed to pump the fluids back into the formation.

In another embodiment, the present invention is directed to an improved wellbore design, which is adapted to separate other fluids and solids from hydrocarbons being produced from the subterranean formation. The wellbore comprises a primary bore having a deviated section, which stimulates convected separation of the other fluids and solids from hydrocarbons during production of the hydrocarbons from the subterranean formation. The wellbore according to the present invention may further comprise a secondary bore, which intersects the deviated section of the primary wellbore at an acute angle and which accumulates one or more of the other fluids and/or solids separating the hydrocarbons. In yet another embodiment, the wellbore according to the present invention may further comprise a tertiary bore which intersects the secondary bore at an acute angle and a pump for pumping the fluids back into the formation.

The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the exemplary embodiments that follows.

DETAILED DESCRIPTION

The present invention is directed to a wellbore completion design that separates water and solids from oil and gas downhole in such a way that the water and solids remain downhole.

The details of the wellbore completion design in accordance with the present invention will now be described with reference to the accompanying drawings. Turning toFIG. 1, one embodiment of a wellbore configuration is shown generally by reference numeral10. The wellbore10comprises a primary bore12and a secondary bore14. The primary bore12in turn comprises a vertical section16, deviated section18and a horizontal section20. The secondary bore14is deviated from the deviated section18or the horizontal section20and intersects the deviated section18or the horizontal section20at an acute angle.

The wellbore10is formed in subterranean formation22by conventional drilling or equivalent techniques. Subterranean formation22in turn comprises an inactive or dead zone24, a producing zone26, and a water containing zone28. As can be seen fromFIG. 1, the vertical section16of the primary bore12is most often formed in a zone24of the subterranean formation22that is non-productive, or not being produced, a highly deviated section18, which may or may not be within the producing section, and horizontal section20formed in the producing zone26of the subterranean formation. The secondary bore14transverses into both the producing zone26and the water containing zone28. The deviated and horizontal sections18and20of the primary bore12and the secondary bore14are formed by conventional directional drilling or equivalent techniques.

The vertical section16of the primary bore12of the wellbore10may be lined with a casing string30, which may be cemented32to the dead zone24of the subterranean formation22. This step can be accomplished using conventional casing techniques. The deviated section18of the primary bore12and the horizontal section20of the primary bore12may also be lined with a casing string, which may also be cemented to the subterranean formation22. Those of ordinary skill in the art will appreciate the circumstances under which the various sections of the primary bore12should be lined with a casing string and whether the casing string should be cemented to the subterranean formation22.

The horizontal section20of the primary bore12is the main section from which the hydrocarbons will be drawn from the subterranean formation. This can be accomplished through several well known techniques. For horizontal wellbores, the most common method currently is to leave the drilled wellbore in this section as an open hole without casing or liner; or by using a liner where the annulus between the formation and the liner is not cemented. This allows the free flow of formation fluids into the openhole. In some wells, the deviated section18and the horizontal section20have a cemented casing. If a non-cemented liner is used, at least some portions of this liner may contain sections of the pipe that are pre-slotted or have pre-drilled perforations, as is well understood by those skilled in the art. In the case of using a solid liner or a cemented casing, after placement into sections18and20, the liner or the casing and cement sheath will usually be connected to the reservoir26by forming a plurality of perforations along the length of the horizontal section20(and possibly deviated section18also) of the primary bore12. This can be accomplished by any one of a number of techniques, including, e.g., but not limited to, conventional explosive charge perforating techniques or by hydrajetting the perforations. In some cases, this may be followed by conventional damage removal or stimulation techniques such as acidizing or hydraulic fracturing. It may be desirable that all or a substantial portion of the deviated section18of the primary bore12not be perforated or fractured. Indeed, it is in this section that the convective separation of the hydrocarbons from other fluids and solids can most easily take place. The presence of perforations and/or fractures in this region may interfere with this process. To facilitate this convective separation, which will be explained immediately below, at least a significant length (possibly about one hundred feet (100 ft)) of the deviated section18of the primary bore12should not be perforated. Furthermore, to facilitate the separation process, the deviation section18of the primary bore12, should be oriented at an acute angle α to the horizontal, which is designated by reference number34. The horizontal line34generally forms an approximate right angle with the vertical section16. The acute angle α is desirably within the range of about 20° to about 70°, and more desirably about 30° to about 60°.

The convective separation process in accordance with present invention is best illustrated inFIG. 2. The hydrocarbons, primarily oil and gas, mixed with other fluids and solids, primarily water and formation particles or fracturing proppants, are forced in a upward direction by either the action of a downhole pump or the reservoir pressure of the formation. Because the water and solids are heavier than the hydrocarbons, i.e., they have a higher specific gravity than the hydrocarbons, they have a tendency to separate from the hydrocarbons and fall to the bottom of the deviated section18of the primary bore12, which because of its inclined nature creates a convective flow, as indicated by the arrow A. The opening of the secondary bore14in turn “catches” the heavier elements, namely the water and solids, into the secondary bore, which operates to accumulate these components, as indicated by the arrow B.

It may be desirable to line the secondary bore14with a section of casing string36, which may be cemented38to the subterranean formation22as required, so as to prevent the seepage of additional water into the secondary bore14. It may also be desirable to form perforations40and possibly also fractures42in the subterranean formation22, which intersect, and thereby communicate, with the secondary bore14, as shown inFIG. 3. An injection pump44could possibly be installed in the toe section46of the secondary bore14. The injection pump operates to pump the separated water back into the water containing formation, and thereby remove it from the system. The injection pump44may operate on a continual or intermittent basis depending upon the amount of water or solids present in the produced hydrocarbons.

The embodiment of the present invention shown inFIG. 4may be a more desirable configuration to use when solids are present in the produced fluids in more than trace amounts. This is because if the solids entering the secondary bore14accumulates excessively (builds up), they may plug the intake on the injection pump44, which is placed directly in the flow path of the water/sand mixture. The embodiment shown inFIG. 4is intended to prevent this from happening when there are more than trace amounts of sand in the production. In this embodiment, the toe section46of the secondary bore14is aligned at an acute angle β from the centerline of the secondary bore. The angle β is desirably between about 5° and about 45°, and more desirably about 15°. The injection pump44is thus placed at an angle to the remaining “straight” section of the secondary bore14. The solids can therefore build up in the straight section of the secondary bore14. It is possible to form a bridge in this section and therefore is not likely to build up in the upward angled toe section46of the secondary bore14, where it could plug the intake to the injection pump44. Accordingly, the solids can partially accumulate in the straight section of the secondary bore14, while the water is pumped back into the water containing formation28via the injection pump44. As with the previously described embodiments, once the sand builds up to the point that it starts to interfere with the flow of the separated hydrocarbons, the sand will need to be removed. This can be done using several techniques well known to those skilled in the art.

Another wellbore completion design in accordance with the present invention is illustrated inFIG. 5. This design is similar to the embodiment shown inFIG. 3. The embodiment ofFIG. 5, however, includes a tertiary bore48. The tertiary bore48intersects, and communicates with, the secondary bore14at an acute angle γ, which is desirably between about 5° and about 45° and more desirably about 15°. In this embodiment, the injection pump44is disposed in the toe section50of the tertiary bore48. The tertiary bore48may also be lined with a section of casing string52, which may be cemented54to the subterranean formation. The section of casing string52prevents the seepage of water into the tertiary bore48. In this embodiment, the perforations56and fractures58(if present) desirably intersect with the tertiary bore48. In this embodiment, the secondary bore14accumulates the solids, which are heavier than the water, and therefore settles in the lower of the two lower bores of the wellbore10. Indeed, the convective effect also occurs in the secondary bore14wherein flow of the lighter element, water, rises to the top part of the secondary bore14and flow of the heavier element, solids, falls to the bottom part of the secondary bore. The water flowing in the top half of the secondary bore14is then directed into the tertiary bore48, wherein the injection pump44forces it back into the subterranean formation22via perforations56and (if present) fractures58. As those of ordinary skill in the art will appreciate the wellbore design shown inFIG. 5can easily be modified such that the tertiary bore48intersects the primary bore12in the deviated section18. In this embodiment, the secondary bore14would operate in the same way but would intersect the tertiary bore48at a point below where the tertiary bore48intersects deviated section18.

In another embodiment of the present invention, the deviated section18of the wellbore10serves both to separate the water and sand from the oil and gas and also to accumulate the water and sand. There is no secondary bore14or tertiary bore48in this embodiment. In order to effectively accumulate the water and sand in this configuration, therefore, it is desirable that the deviated section18of the wellbore10be unperforated and unfractured. This will thereby prevent the seepage of water and other elements into the wellbore10, which may interfere with the production of the hydrocarbons and the accumulation of the separated elements. In one exemplary version of this embodiment, the deviated section18of the wellbore is about one hundred feet (100 ft) or more, as noted above. It is particularly important that the unperforated portion of the deviated section18of the wellbore, which is used for the separation of the water and sand from the hydrocarbons, be of sufficient length that it does not become plugged before desired. Furthermore, as also noted above, the deviated section18of the wellbore10is desirably formed at an acute angle α to the horizontal34, which is desirably within the range of about 30° to about 60°, and more desirably about 45°.

FIG. 6illustrates this embodiment as incorporated into five different potential conventional wellbore configurations. The conventional wellbore configurations are identified by the dashed lines and labeled with the designations I-V. The wellbore configurations according to the present invention, which are modifications to the conventional designs that incorporate the unperforated deviated section18, are indicated by the solid black lines and labeled with the designations I′-V′. The Type V conventional design has two modifications in accordance with the present invention shown, namely Type V′ and Type V″. The circles shown inFIG. 6indicates a desirable location of a production pump or production assembly tip. As can be seen fromFIG. 6all the pumps or production assembly tips in the conventional wellbore designs are located in the production zone26. The production pumps or production assembly tips in the wellbore configurations in accordance with the present invention, however, are all located above the production zone26, namely in the non-producing zone24. Furthermore, the production pumps or production assembly tips in the wellbore configurations in accordance with the present invention are all located in the unperforated portion of the deviated section18of the wellbore10. The separation of the water and solids from the hydrocarbons will occur, via the convective separation phenomenon described above, below the pumps or production assembly tips, so that the only fluid that encounters the pumps or production assembly tips is a mixture of essentially hydrocarbons with no or very little water or solids.

As those of ordinary skill in the art will appreciate, the present invention has application in virtually any type of well. For example, it can be used in multilateral wells and wells with fish bones as well as other wells not mentioned herein. Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. While numerous changes may be made by those skilled in the art, such changes are encompassed within the spirit of this invention as defined by the appended claims