Patent Application
20050173156
The present invention is directed toward drilling bores in earth formations, and more particularly to a horizontal bore cryogenic drilling method.
In many aquifers, the ability to produce water by traditional vertical wells is limited by several factors. In the case of thin aquifers, vertical wells do not allow a long enough section of screen to be installed across the productive formation. This limits the area of the seepage base that can transmit water into the well and reduces the amount of available drawdown that can be created to induce flow toward the well. Both of these factors prevent vertical wells from producing as much water as could be potentially extracted. In other cases, the most productive portion of the aquifer is located under a physical obstruction where a vertical well cannot be installed. These obstructions typically include rivers, lakes, wetlands, structures or other areas where a wellhead is not permitted or access for a vertical drilling rig is impractical.
Horizontal wells are often constructed near or under sources of groundwater recharge, such as rivers, lakes or wetlands. As used herein, “horizontal” well or bore means a well or bore that is not exclusively vertical, but has a substantially horizontal or sub-horizontal portion substantially parallel to the ground surface that allows the horizontal bore to access aquifers of limited depth or to access aquifers blocked from vertical access by obstructions as discussed above. Installing a screen under a source of recharge has the effect of inducing additional recharge to the aquifer. This can substantially increase the sustained yield of a horizontal well by capturing surface water.
Horizontal water supply wells have been traditionally constructed using radial horizontal collector wells, also known as Ranney® type wells. Radial horizontal collector wells are constructed with large vertical caissons, several feet to tens of feet in diameter, installed to the depth of interest. Well screens or casings are jacked or otherwise advanced horizontally from the caisson to the geologic formation. The well screens or casings form horizontal laterals that conduct water from the formation into the caisson where it is pumped to the surface. Building a radial horizontal collector well using this conventional construction technique is a difficult and lengthy undertaking. For this reason, radial horizontal collector wells are often several times the cost of a traditional vertical well. In addition, the laterals cannot generally be steered or directed other than by simple linear protection from the caisson. The method has limited ability to project laterals through boulders, cobbles or other obstruction or difficult drilling conditions.
An additional problem with this conventional construction technique is fluid invasion into the open face of the lateral cannot be controlled during construction. This creates a need to pump significant volumes of water to keep the caissons from flooding during construction. The lateral jacking process usually requires workers to be at the bottom of the caisson. This forces workers to endure wet conditions in a confined space below the water table with all the inherent risks and safety hazards that can occur under such conditions.
Horizontal directional drilling has been used to install utilities such as pipelines and cables, to extract geologic samples, and for various other purposes. These methods involve mud rotary drilling in which the bit enters the ground from a trench or shallow angle from the surface. The bit is directed horizontally as it is pushed from the surface via the drill string. In some recent manifestations, the drill bit can be steered down hole using several cutting heads on a down hole drilling motor. The bit can be steered to direct the bore hole vertically or horizontally. Directionally drilled horizontal holes can be drilled to a point of underground termination. The bit and drill string may then be removed and the well is completed from the opening of the bore hole at the surface. This type of horizontal hole is called a blind hole as the end of the hole is never seen. Horizontal bore holes can also be steered to the surface and terminated above ground. These two sided completions are commonly called continuous bores and allow materials to be introduced into the hole from either side in order to complete construction of, for example, a water supply well.
One known maker of horizontal directional drills is Vermeer Manufacturing Company of Pella, Iowa. Examples of their horizontal directional drills can be seen on their website.
All known existing horizontal directionally drilled bore holes use drilling mud to keep the hole from collapsing, prevent the invasion of large volumes of formation water, remove the cuttings from the bore hole as the drill string advances and provide power and cooling for the down hole drilling motor. The drill muds fall into two major categories, muds based on inorganic clay minerals, such as bentonite, or organic polymers known as biosolid muds. While the use of drilling mud is necessary for the construction of the bore hole, either type of mud produces undesirable effects on the formation around the bore hole. The drilling mud is kept under positive hydraulic head in the bore hole to keep the formation from collapsing. The hydraulic head causes the mud to exfiltrate from the bore hole into the adjacent formation. As it penetrates the formation, the mud creates a zone of invasion which reduces the permeability of the formation adjacent to the bore hole. This has the desirable effect of reducing infiltration of formation water into the bore hole during well construction, but also creates a zone of low permeability that limits the ability of water to flow into the bore hole after construction is completed.
Horizontally directionally drilled bore holes are most commonly used to install cables and pipelines. In these applications, mud invasion of the formation is not a significant concern. However, recently horizontally directionally drilled bore holes have been used to install well screens for environmental remediation wells and for high capacity water supply wells. In these applications, the zone of low permeability created by mud invasion significantly reduces the production capacity of the well. To date, efforts to remove the drilling mud from the invaded zone have proven to be expensive and of only limited effectiveness.
Additional limitations of horizontal directionally drilled borings using drilling muds are commonly encountered. The method has limited ability to prevent collapse of the bore hole in formations containing cobbles and loose gravel. This can cause the formation to collapse on the drilling string. In addition, there is a tendency for cuttings to settle out of the mud forming an obstruction on the bottom of the horizontal portion of the hole. This can also trap the drill string in the hole. Finally, a curved radius of the bore hole is used as a fulcrum to bend the drill string from sub-horizontal to horizontal. In many applications, the formations lack the structural integrity to withstand the stress as the drill rod is forced into the formation at the top of the bore hole. This results in an irregularly shaped bore hole known as a key seat. Key seats can trap the bit in the hole for blind well installations. As a result, grouted casings must be installed across the curved radius of the sub-horizontal portion of the bore hole for longer blind well completions or when dealing with soft formations. This increases the cost and complexity of the drilling operation.
In the drilling of vertical wells, problems of contamination of the area adjacent the well bore by drilling muds has been recognized. Also, where vertical wells have been drilled in earth formations having a high water content, problems have been experienced in extracting water fast enough to effectively advance the drill. In addition, particularly in places where certain shales swell or hydrate in the presence of an influx of water into the well bore, problems have been encountered with the shale becoming loosened and sloughing into the hole necessitating large quantities of shale and cuttings to be lifted out of the well bore. Indeed, if enough shale is loosened, the drill string may even become stuck.
One solution to these problems that has been proposed is using cryogenic gas or liquids as a drilling mud to form a frozen boundary around the vertical bore as it is drilled. Vertical cryogenic drilling methods are described in Maguire, U.S. Pat. No. 3,612,192 and Weaver, U.S. Pat. No. 3,774,701. However, there is no suggestion in these references of the desirability of using vertical cryogenic well drilling techniques for the construction of horizontal bores.
Rebhan, U.S. Pat. No. 4,516,876, describes a tunnel construction technique wherein a pair of vertical caissons are installed at opposite ends of a horizontal tunnel segment. A pilot hole is then drilled between the caissons. A freezing pipe is inserted into the hole and a cooling agent is supplied to the hole to freeze soil adjacent the freeze pipe. Upon creating a freeze zone of sufficient diameter a rotary excavating device rotates around the freezer work pipe to excavate the tunnel. Upon completing excavation of the lengthwise segment of the tunnel, the freezer work pipe is advanced to create a further length of freeze zone and casings can be installed in the newly excavated tunnel. The technique of Rebhan does not allow for construction of cryogenic horizontal wells from the ground surface, nor does it allow the use of directionally controlled drilling equipment.
The present invention is directed toward overcoming one or more of the problems discussed above.
A first aspect of the invention is a method of forming a horizontal bore in an earth formation. A pilot hole is formed of a first select diameter along a desired path of the horizontal bore. A grindable casing, preferably a high-density polyethylene casing, is inserted into the pilot hole. A cryogenic fluid is flowed through the grindable casing to form a freeze zone of frozen moisture adjacent to the grindable casing having a second selected diameter. A primary bore is formed having a third select diameter greater than the first select diameter and less than the second select diameter within the freeze zone along the desired path of the horizontal bore with the grindable casing in place. The second diameter is selected to be sufficiently greater than the third select diameter to prevent collapse of the freeze zone.
Forming of the pilot hole is preferably accomplished using a directionally controlled drill string driven by a cryogenic fluid or conventional drilling mud. Preferably, the bore is constructed from a ground surface overlying the earth formation and the horizontal bore includes a transverse portion transverse the ground surface and a horizontal portion substantially parallel to the ground surface. Preferably, for a water well completion, a screen or screen and gravel pack is installed in the horizontal portion of the primary bore while the freeze zone remains sufficiently frozen to prevent collapse of the primary bore. A casing is installed between the ground surface and the screen. A submersible pump may be installed in either the transverse portion or the horizontal portion. Alternatively, a vertical shaft may be provided between the ground surface and the horizontal portion of the bore and a pump may be provided proximate an intersection between the vertical shaft and the horizontal portion of the bore. In a highly preferred embodiment, the second select diameter defines a freeze zone of sufficient structural integrity to withstand mechanical forces of a directional drill string used in forming the primary bore as the primary bore transitions from the transverse portion to the horizontal portion without collapse of the primary bore.
A second aspect of the present invention is a method of forming a horizontal bore in an earth formation which includes providing a drill string having a conduit communicating with a cutting tool for engaging the earth formation. A cryogenic fluid is flowed through the conduit and the cutting tool to drive the cutting tool and remove cuttings from a bore formed by the cutting tool. The cutting tool is directed into an earth formation and a freeze zone is formed in the earth formation in advance of the cutting tool by the cryogenic fluid flowing through the cutting tool. The cutting tool is then advanced into the earth formation to form the horizontal bore at a rate enabling continued formation of a freeze zone in advance of the cutting tool of sufficient diameter to prevent collapse of the bore as the cutting tool is advanced.
The method may further include initially directing the cutting tool into the earth formation at a ground surface above the formation and advancing the cutting tool to form a transverse portion of the horizontal bore transverse to the ground surface and a horizontal portion of the horizontal bore substantially parallel to the ground surface. The freeze zone is preferably formed to have a large enough diameter that it has sufficient structural integrity to withstand mechanical forces of the drill string as the bore transitions from the transverse portion to the horizontal portion without collapse of the bore. The method may further include installing a well screen or well screen and gravel pack within the horizontal portion of the bore while the freeze zone remains sufficiently frozen to prevent collapse of the horizontal portion of the bore. A casing is installed to connect the screen to the surface. A submersible pump may be installed in one of the transverse portion or the horizontal portion of the well bore. Alternatively, a vertical shaft may be provided between the ground surface and the horizontal portion of the bore. A vertical line shaft or submersible pump is then provided proximate to an intersection between the vertical shaft and the horizontal portion of the bore. The horizontal bore cryogenic drilling method in accordance with the present invention eliminate the need to use conventional drilling muds which can both pollute the earth formations around a well screen and plug the formation to prevent the efficient flow of water into a horizontal well bore. The cryogenic fluid further allows freezing of formation around the bore hole which allows the earth formation to take on the character of hard rock. This not only improves the structural integrity in the vicinity of the bore, but it eliminates infiltration of formation fluid and eliminates exfiltration of drilling fluids. The cryogenic technique further provides a solid formation which enables the use of drilling hammers as an alternative to rotary drills which can speed construction of the bore. In addition, the frozen cuttings act like dry powdered rock, which can be more efficiently removed from a bore by a cryogenic drilling fluid. The technique also eliminates the need to install grouted casings across the radius of the bore hole where it transfers from transverse to horizontal, thus further speeding and simplifying construction of the bore. In addition, the cryogenic technique renders irrelevant encountering cohesive soils such as clay which might otherwise form problematic clay balls. Finally, physical changes to the formation around the bore hole created by the cryogenic method are temporary. The formation will revert to its natural conditions shortly after circulation of the cryogenic fluid is stopped. By way of contrast, mud rotary methods require elaborate well development processes to remove the mud invasion from the formation and these processes have proven unsatisfactory.
The present is invention contemplates the use of standard horizontal directional drilling equipment with only minor modifications to accommodate the cryogenic fluid. One representative manufacturer of horizontal directional drills is the Vermeer Manufacturing Company of Pella, Iowa. These horizontal directional drills allow the formation of bores having an initial portion transverse a surface of the earth which then transitions to a horizontal portion of a horizontal bore.
As mentioned above, use of cryogenic fluids may require modifications to standard horizontal directional rigs. For example, it will likely be necessary to provide a substitute material for low carbon steel used in conventional drill strings because the low carbon steel may become too brittle at cryogenic temperatures. For vertical drill strings, use of aluminum drill pipe or steel pipe containing 9% or more nickel has been suggested. Weaver, U.S. Pat. No. 3,774,701, at column 2, line 68-73. Use of cryogenics may also require modification of conductor pipe, casing head, bits, rotary hose and circulating head gaskets used in conventional flow horizontal drilling systems.
As used herein, cryogenic fluid means chilled gas, liquefied gasses or cryogenic brine solutions. Representative chilled gasses may include nitrogen, natural gas, carbon dioxide, methane, propane, neon and the like. Liquefied gases may include liquefied nitrogen, propane, carbon dioxide, methane, natural gas and the like. Obviously, modifications to conventional horizontal directional drill equipment will be a function of a particular cryogenic fluid selected.
Weaver, U.S. Pat. No. 3,774,701, the contents of which are expressly incorporated herein by reference, discloses use of compressed air as a cryogenic gas, steps to remove moisture from the air and modification of a vertical drill bit for use with chilled compressed air. Maguire, U.S. Pat. No. 3,612,192, which is also expressly incorporated by reference herein, similarly teaches a vertical cryogenic drill system using chilled gas such as air.
A first horizontal cryogenic drilling method is disclosed with reference to
The grindable casing or freeze tube may be made of any material having sufficient structural integrity to be axially inserted into pilot bore, sufficient structural integrity at cryogenic temperatures to reliably flow cryogenic fluid to the pilot bore and yet be soft enough to be drilled up with conventional drilling equipment. A plastic casing such as one made of high density polyethylene (HDPE) or other suitable plastics may be preferred. For blind bore construction, the grindable casing may consist of an outer pipe and an inner pipe having an annular space between the two pipes to conduct the cryogenic fluid to or from the drill bit. For continuous well construction, the grindable casing may consist of a single pipe.
Referring next to
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In the embodiment illustrated in
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In an alternative design illustrated in
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Another aspect of the present invention is a single pass horizontal bore cryogenic drilling method. This method can be illustrated with reference to
In constructing the horizontal bore, the cutting tool is directed into an earth formation and the cryogenic fluid begins forming the freeze zone. A freeze zone of sufficient structural integrity to prevent collapse of the bore is formed. The cutting tool is then advanced along a select path into the earth formation to form the bore at a rate which enables continued formation of the freeze zone in advance of the cutting tool as illustrated in
The horizontal bore cryogenic drilling methods described above allow for expedient and economic drilling of water supply wells where horizontal wells are of particular advantage. The cryogenic techniques eliminate the need for drilling muds which cannot only contaminate water formations, but lead to plugging of the well bore/earth formation interface wall and thus inhibiting of efficient operation of the horizontal well. The freeze wall formed during the cryogenic horizontal well drilling method prevents collapse of the drilling hole during drilling and further allows for installation of gravel packs, screens and casings without collapse of the bore hole. These many advantages can be provided by relatively simple modifications of preexisting directional horizontal drilling equipment.
While the particular embodiments herein are primarily described for use in forming horizontal water supply wells, the methods may also be employed in any application where preventing invasion of drilling muds into earth formations is desired. For example, in the construction of environmental horizontal wells for remediation or construction of groundwater basin recharge wells, geotechnical borings, dewatering wells, borings above the zone of saturation, or injection wells of various types. This invention specifically contemplates horizontal to sub-horizontal borings used to install instrumentation and equipment for a variety of geotechnical purposes, to temporarily stabilize ground for a variety of purposes, or to collect samples of soil or in-situ formation fluids in a stabilized solid form.
