Patent Description:
The development of technologies for exploration for and access to minerals in subterranean environments has made tremendous strides over past decades. While wells may be drilled and worked for many different reasons, of particular interest are those used to access petroleum, natural gas, and other fuels. Such wells may be located both on land and at sea. Particular challenges are posed by both environments, and in many cases the sea-based wells are more demanding in terms of design and implementation. A particular issue in drilling involves extreme levels of vibration that can be caused by interaction of.

Drill string vibrations are a significant concern during drilling operations, and are a common cause of downhole tool failures, failures of more sensitive equipment, such as components of a critical bottom hole assembly (BHA), or other part of the equipment. Drill string vibrations are typically categorized in three ways: axial (the drill string is v ibrating along the axis of drilling), lateral (the drill string is vibrating perpendicular to the axis of drilling), and torsional (the drill string is rotating along the axis of rotation). Vibrations are induced in a multitude of ways including at the drill floor, the drill bit cutting rock, rotating an imbalanced mass (sections of the BHA), etc..

There is a need in the art for improved ways of reducing such vibration, or for at least mitigating or localizing some of its effects.

<CIT> discloses a method and apparatus for drilling highly deviated wells. It is disclosed that a drilling assembly is attached to a drill string. The drilling assembly includes a bent sub, a pony collar attached to the bent sub, a motor with a bent housing, and a bit.

<CIT> discloses a method and apparatus which include drilling a bore hole in a horizontal direction with a drill bit, a bent housing portion, and a mud motor by rotating the drill bit, the bent housing portion, and the mud motor with drill pipe comprising an aluminum pipe section. The method and apparatus also include stopping rotation of the drill pipe and performing a slide by rotating the drill bit with the mud motor to advance the drill bit, the bent housing portion, the mud motor, and the drill pipe in the borehole so that the aluminum pipe section moves axially along the bore hole in the horizontal direction. The method and apparatus also include continuing to drill the bore hole by rotating the drill bit, the bent housing portion, and the mud motor with the drill pipe.

<CIT> discloses a method for drilling a well bore having a vertical portion, a curved kick-off portion, and a horizontal portion. The length of the horizontal portion is extended by using drill pipe having an aluminum tube and steel tool joints to reduce the weight of the pipe string in the horizontal portion and reduce the friction resisting movement of the drill pipe along the low side of the well bore. In addition, the length of the joints of aluminum drill pipe is reduced to between <NUM>-<NUM> metres (<NUM>-<NUM> feet) to substantially increase the buckling strength of each joint.

It is therefore the object of the present invention to provide an improved drill string and corresponding well system for reducing vibrations in drilling.

In accordance with certain aspects of the technology, a drill string comprises a vibration damping drill pipe section assembled at a location where vibration damping is desired, the vibration damping drill pipe section comprising a plurality of pipe segments made of a vibration damping material, and a further drill pipe section made of a different material less able to dampen vibration experienced by the drill string during drilling.

In accordance with a further aspect, the drill string comprises a drill bit, a bottom hole assembly adjacent to the drill bit, and a vibration damping drill pipe section adjacent to the bottom hole assembly opposite to the drill bit, the vibration damping drill pipe section comprising a plurality of pipe segments made of a vibration damping material. A further drill pipe section is disposed adjacent to the vibration damping drill pipe section opposite the bottom hole assembly and made of a different material less able to dampen vibration experienced by the drill string during drilling.

The techniques also provide a method for making a drill string, comprising assembling a drill bit and bottom hole assembly, assembling a vibration damping drill pipe section adjacent to the bottom hole assembly as drilling advances into a well, and assembling a further drill pipe section adjacent to the vibration damping drill pipe section opposite the bottom hole assembly and made of a different material less able to dampen vibration experienced by the drill string as drilling advances further into the well.

The systems and methods described allow for significantly reduced vibration of drill strings and particularly of portions of the drill strings in the region of sensitive equipment, such as the BHA. The techniques may be based upon the use of low modulus and low density materials in a system that can dampen vibrations, and that can be applied to an oil and gas drilling environment with the use of aluminum drill pipe, titanium drill pipe, or composite drill pipe that compliments conventional steel pipe. In some embodiments materials that may be used may include ductile iron, which may provide vibration damping due to its microstructure. For example, the low modulus and density of aluminum can reduce both the duration and severity of torsional vibrations in a stick-slip type dysfunction. The reduction in severity of uncontrolled torsional oscillations will reduce the additional strain on threaded connections throughout the BHA and drill string, as well as the impact caused by lateral vibrations, and the amplitude of axial vibrations. This overall reduction in vibrations can have the benefit of increasing the life of sensitive downhole components (and the drill string elements themselves), and increasing the efficiency of drilling operations.

Turning now to the drawings, and referring first to <FIG>, a well system is illustrated and designated generally by the reference numeral <NUM>. The system is illustrated as an onshore operation located on the earth's surface <NUM> although the present techniques are not limited to such operations, but may be used in offshore applications, in which the drilling and service equipment and systems described would be located on a vessel or platform, and the well would be located below a body of water. In <FIG>, the underlying ground or earth is illustrated below the surface such that well equipment <NUM> is positioned near or over one or more wells. One or more subterranean horizons <NUM> are traversed by the well, which ultimately leads to one or more horizons of interest <NUM>. The well and associated equipment permit, for example, accessing and extracting the hydrocarbons located in zones of interest, depending upon the purpose of the well. In many applications, the horizons will hold hydrocarbons that will ultimately be produced from the well, such as oil and/or gas. The well equipment may be used for any operation on the well, such as drilling, completion, workover, and so forth. In many operations the installation may be temporarily located at the well site, and additional components may be provided. However, in the present context, the tubular strings described are drill strings used to access the horizons by cutting or grinding rock and other subterranean formations as they are traversed.

In the illustration of <FIG>, equipment is very generally shown, but it will be understood by those skilled in the art that much this equipment is conventional and is found in some form in many such operations. For example, a derrick <NUM> allows for various tools, instruments and tubular strings to be assembled and lowered into the well, traversing both the horizons <NUM> and entering or traversing the particular horizons of interest <NUM>. Well or surface equipment <NUM> will typically include draw works, a rotary table, generators, instrumentations, and so forth. Control and monitoring systems <NUM> allow for monitoring all aspects of drilling, completion, workover or any other operations performed, as well as well conditions, such as pressures, flow rates, depths, rates of penetration, and so forth.

In accordance with the present disclosure, many different tubular stocks (e.g., drill pipe) may be provided and used by the operation, and these may be stored on any suitable racks or other storage locations. In <FIG> a first of these is designated tubular <NUM> storage <NUM>, and the second is designated tubular <NUM> storage <NUM>. As will be appreciated by those skilled in the art, such tubular products may comprise lengths of pipe with connectors at each end to allow for extended strings to be assembled, typically by screwing one into the other, or two tubular products connected via a single coupling. Different tubular stocks are used here to allow the operation to balance the technical qualities and performance possibilities of each against their costs. That is, one material may be selected for its relative strength but lower cost (e.g., steel), while the other is selected based upon its superior ability, such as low density and modulus, to be inserted into extended portions of the well for vibration damping, although it may be more costly than the first material. In presently contemplated embodiments, this second tubular stock may comprise, aluminum alloys, for example, but possibly also certain titanium alloys, composite materials, or metal matrix alloys. As discussed below, the operation judiciously selects which material to use based upon the nature of the well, the well position and geology, and the desire to reduce vibration during drilling.

In the illustration of <FIG>, a drill string comprises a first, generally vertical section <NUM> that extends through the upper horizons <NUM>, and an off-vertical section <NUM> that extends through at least a portion of the zone of interest <NUM>. The vertical section is formed to access the horizon of interest, and may extend to any desired depth, such as <NUM>, <NUM> metres (<NUM>,<NUM>) feet to <NUM>, <NUM> metres (<NUM>,<NUM> feet). The off-vertical section may extend at any desired angle from the vertical section, which may be generally perpendicular to the vertical section, although other angles for this section may be used. In practice, a well or a well system may access a number of locations in one or more horizons of interest by directional drilling to create one or more such off-vertical sections. The overall drill string <NUM> is illustrated as already deployed in the well for furthering the well bore through various formations and ultimately to the one or more of the formations of particular interest.

In this illustrated embodiment, the overall drill string <NUM> extends into a generally vertical section <NUM> of the wellbore, and into a generally horizontal section <NUM>, as the wellbore is advanced by action of the drill bit <NUM>. The drill string <NUM> extends a length <NUM> through the vertical section <NUM> of the well and through a length <NUM> of the off-vertical section <NUM>, ultimately to the advancing bit <NUM>. The drill string comprises a tubular string (e.g., pipe) that is run into the well during drilling. Such strings may comprise any suitable length of tubular products, and the number, size, and materials used for these will depend upon a number of factors, but typically the location of the horizon of interest (e.g., its depth and the length of the off-vertical section, if any), the distance to a location of interest, the depth of the water, if offshore, and so forth. In the illustrated embodiment, a bottom hole assembly or BHA <NUM> is positioned immediately adjacent to the bit <NUM>. A length of vibration damping drill pipe <NUM> is then positioned adjacent to or near the BHA to aid in reducing vibrations in the drill string.

The drill string <NUM> and will typically be assembled by the well equipment, drawing from the tubular materials stored as discussed above. That is, various tools (e.g., drill bit, connectors, BHA with its associated instrumentation) are first assembled and placed into the well, followed by lengths of drill pipe by taking the pipe sections from the storage, threading them end-to-end, and deploying them progressively into the well. In presently contemplated embodiments, some of the drill string is made of vibration damping materials, such as aluminum alloy, for example, or another material that enables the drill string to attenuate the levels or effects of vibration (e.g., titanium alloy, composite material, metal matrix alloys). The other sections of drill pipe may be made of conventional materials, such as steel. As noted above, vibration damping materials suitable for use in the present techniques may include ductile iron, at least partially due to the damping abilities of its microstructure. The tubular sections assembled in this way may comprise, for example, multiple sections of standard length (e.g., <NUM> or <NUM> metres (<NUM> or <NUM> foot) sections) each having industry standard end connectors to facilitate their assembly. By way of example only, while the vertical section of the well may extend as much as <NUM> to <NUM> or more metres (<NUM>,<NUM> to <NUM>,<NUM> or more feet) vertically into the earth (note that the "vertical" section need not be strictly vertical, but may be inclined in at least a part of the well), the off-horizon section may extend another <NUM>,<NUM> metres to <NUM>,<NUM> metres (<NUM>,<NUM> to <NUM>,<NUM> feet). In some embodiments, as discussed below, the vibration damping sections may be placed closest to the BHA, although other sections may be placed at other locations in the drill string.

Axial vibrations are typically manifestations of compressive waves that travel along the axis of the drill string. Also called "bit bounce," these vibrations cause the cutters on the drill bit to lose depth, reducing effectiveness of the drilling operations. In extreme cases, the drill bit loses all contact with the formation, and re-engages at a high velocity. This can cause undesirable damage to the bit.

Torsional vibrations are sometimes referred to as "stick-slip" vibrations. These are variations in the rotational speed in the drill string. In extreme cases (full stick-slip), the drill bit will stop rotating entirely, allowing for torsional energy to build up in the drill string. This torsional energy unwinds in an extremely high angular velocity release. This build up and release of the torsional energy causes high stress cycles on the drill string, and on the threaded connections in particular. These vibrations are most severe closer to the drill bit, which is typically also where the majority of sensitive components are located.

More particularly, torque is applied from the rig floor and transferred via the drill string to the drill bit. This turning force, along with the weight of the drill string, allows the drill bit to cut through subsurface geologic formations. The drill bit is impregnated with hardened inserts, or cutters, that are angled such that when an axial force and rotational moment are applied, will shear off small sections of rock called cuttings. The cuttings are traditionally carried to the surface via a thickened fluid called "drilling mud" which is pumped from the surface through drill string, and moves back to surface through the annulus formed between the outside of the drill pipe and the newly cut wellbore. This process allows the drill string to advance through the formation.

When drilling normally, the rotation of the drill bit is steady and predictable. A dysfunction can occur where the cutters momentarily get stuck, or "stick," on a section of rock. Regardless of any sticking or stopping of the bit the drilling rig is still turning the drill string at the surface, which causes torsional energy to build up in the drill string. After enough time, the increased torsional energy allows for the drill bit to destroy the rock that it was stuck on, and be released, or "slip. " The built up torsional energy dissipates through the bit in the form of increased rotational speed for a short period of time, until the excess torsional energy is exhausted. This dysfunction can occur repeatedly during drilling operations. When this happens, the drill bit and tools in the drill string are forced to accelerate at a rate beyond typical operations. This change in rotational speed also affects the amount of rock that is cut during each rotation of the bit, slowing down the operations as a whole. These uncontrolled torsional oscillations of the drill string reduce the effectiveness of the drilling operations and cost the operator time and money. There are various ways to reduce these vibrations, including momentarily pausing drilling operations to allow for the vibrations to dampen and dissipate naturally.

Lateral vibrations are caused by rotating elements of the drill string, particularly elements with a mass imbalance, coupled with friction against the wellbore wall. This causes the drill string to oscillate up and down the wellbore wall, and can cause the drill string to break contact with the wellbore, and reengage at a high velocity. Typically these vibrations are categorized as "forward whirl," where the oscillation of the drill string in the borehole is the same rotational direction as the drill string, and "backward whirl," where the oscillation is opposite of the rotation of the drill string. A third form, "chaotic whirl," occurs when the oscillations are not in a pattern which correlates with the drill string rotation. These vibrations can cause damage to sensitive internal components. □Lateral movement is also caused by torsional vibrations. When the torsional energy is released, drill string elements forcibly shake in the wellbore and can impact the wellbore walls at a high velocity.

In particular, all drilling activity causes movement of the tubulars perpendicular to the axis of the drill string. During rotation of the drill string friction is generated between the wellbore wall and the tubulars because of this rotation. This friction forces the tubular to ride up one side of the wellbore, and along with other forces including mass imbalances in some of the drilling tools, causes the drill string to oscillate up and down the well bore wall. In some cases, this movement can become erratic. The vibrations resulting from the "whirl" mentioned above are generally referred to as "lateral vibrations" and in extreme cases, these vibrations, particularly backward whirl, cause the drill string to make contact with the wellbore walls with a high velocity and acceleration, called shock, which can cause damage or premature failure to drilling tools.

Mechanical connections affected by the vibration become fatigued far more quickly than what would be expected under normal operations. Sensitive electronic or mechanical components in a measuring while drilling (MWD) tool are especially prone to damage with this type of vibration. These vibrations also cause energy intended to be transferred to the bit for the purpose of cutting rock to be expelled prematurely throughout the drill string, reducing the rate at which the drill bit cuts rock.

Once this vibratory pattern has been realized in the drill string, measures are often taken to resolve it as quickly as possible. These measures can include again momentarily stopping the drilling operations completely and allowing for the vibrations to dampen and subside on their own. This solution is not ideal as it reduces the overall effectiveness of the operations. If a sensitive component breaks downhole, the operator is forced to either continue drilling "blind" or without the information this tool provides, or do a "trip" in which the drill string is pulled to surface so the broken tool can be fixed or replaced. These scenarios will likely reduce the quality of the hole being drilled, and cost the operator additional time and money.

More generally, all such vibration reduces the efficiency of the drilling operation. That is, ideally, all energy input to the drill string should result in cutting or removal of the underground formations and advancement of the drill string. Vibration ultimately consumes a portion of this energy, reducing the efficiency of the operation. Any reduction in the amount or effects of the vibration should improve this drilling efficiency.

The techniques described allow for reduction, damping, attenuation, or reduction of the effect of some or all of these forms of vibration. In particular, introducing into the drill string a specified length of drill pipe made of a vibration damping material (e.g., aluminum) can reduce the magnitude and duration of both torsional and lateral vibrations. Due to the low modulus and low density of such alloys, the material is able to absorb vibrations that would otherwise be transmitted to other components in the drill string. A relatively small amount of aluminum drill pipe may suffice relative to the length of the entire drill string. Currently this length is theorized to be between <NUM> and <NUM> metres (<NUM> and <NUM>,<NUM> feet) in a drill string that can be between <NUM>,<NUM> and <NUM>,<NUM> metres (<NUM>,<NUM> and <NUM>,<NUM> feet) overall. In some embodiments, the length of a vibration damping section may be reduced to one stand (typically three <NUM> metres (<NUM> foot) joints, or <NUM> metres (<NUM> feet)). Introducing the aluminum drill pipe would reduce delays in drilling operations and avoid damage done to sensitive components, significantly increasing the effectiveness of the drilling operations.

<FIG> illustrates a section of a drill string assembled to reduce vibration. In this illustration, the drill bit <NUM> is shown adjacent to the BHA <NUM>. The vibration damping drill string section or stand <NUM> is shown as comprising <NUM> segments of pipe <NUM>, with screwed connections <NUM> between them and at ends of the section. At the upper end of the vibration damping section <NUM> begins a section of conventional drill pipe <NUM>. The vibration damping section extends over a desired length <NUM> selected to provide the desired vibration damping. Presently contemplated lengths <NUM> may between <NUM> and <NUM> metres (<NUM> and <NUM>,<NUM> feet) in length, and may be made up of pipe segments of <NUM> or <NUM> feet (standard lengths). By comparison, the BHA may be some <NUM>-<NUM> metres (<NUM>-<NUM> feet) in length, while the overall drill string will typically be many thousands of feet long.

In some embodiments and environments it may be useful to provide more than one vibration damping section. <FIG> illustrates such a drill string. In this case, a first vibration damping section <NUM> is again provided near the BHA <NUM>, with a section of conventional steel pipe <NUM> connected above it. Then above that section, another length of vibration damping pipe <NUM>' if provided, followed by another section of conventional drill pipe <NUM>'. Further sections of vibration damping pipe may also be provided further along the drill string. It should be noted, as well, that vibration damping sections may be placed anywhere along the string, with multiple such sections being separated by conventional tubular products. In some embodiments, for example, it may be useful to place vibration damping sections every two or more thousand feet. Such placement may depend upon such factors as the size of the tubular product, the loads encountered, the well conditions, and so forth.

In certain well and borehole profiles and trajectories, such vibration damping sections may be judiciously located to provide desired damping in regions where such vibration is anticipated to be particularly troublesome. <FIG> illustrates an application in which a wellbore has vertical and off-vertical sections <NUM> and <NUM> as discussed above, with a heel section <NUM> transitioning between the two. A vibration damping drill pipe section <NUM> is here again positioned adjacent to the BHA <NUM>. But to help reduce anticipated vibration above the heel section <NUM> of the wellbore, the drill string has a further vibration damping section <NUM>' that may be added to the drill string in a location that will be deployed at, around, or above the heel section.

It is believed that the presence of the vibration damping drill pipe sections, even in relatively short sections as compared to the overall drill string may significantly affect the vibration experienced by the drill string, and particularly by those components near the vibration damping sections, such as the BHA and/or the drill bit. <FIG> is a graphical representation <NUM> of anticipated effects on vibration at such locations. In this illustration, vibration magnitude <NUM> is shown by a vertical axis over time along a horizontal axis <NUM>. The dashed trace <NUM> represents a vibration profile of a conventional drill string at a location of the BHA or drill bit. Significant peaks <NUM> can be anticipated at a frequency corresponding to the dynamics of movement of the end of the drill pipe during drilling. A vibration profile of a drill string having at least one vibration damping section adjacent to this location is represented by the solid trace having significantly reduced peaks, and ultimately settling into a higher frequency, lower peak, and lower variability dynamic region <NUM>.

Similar attenuations are anticipated for drill strings having more than one vibration damping sections, as illustrated in <FIG>. Here, a drill string similar to that of <FIG> is shown along with vibration profile comparison graphs <NUM> and <NUM> at locations adjacent to the vibration damping sections.

The material properties believed to be of particular interest in reducing vibration include modulus of elasticity, density, and damping characteristics. Regarding the modulus of elasticity, conventional steels used for well tubulars have a modulus typically on the order of <NUM> GPa (<NUM> Mpsi), with typical ranges of <NUM> to <NUM> GPa (<NUM> to <NUM> Mpsi). Aluminum alloy tubulars suitable for the present techniques have a modulus typically on the order of <NUM> GPa (<NUM> Mpsi), with typical ranges of <NUM> to <NUM> GPa (<NUM> to <NUM> Mpsi). Titanium tubulars contemplated for the present techniques, on the other hand, have a modulus typically on the order of <NUM> GPa (<NUM> million psi), with typical ranges of <NUM> to <NUM> Gpa (<NUM> to <NUM> Mpsi). Suitable composites can be made to have a very low modulus, such as on the order of <NUM> GPa (<NUM> Mpsi) if required. Regarding the relative density of such materials, typical steel has a density of <NUM>,<NUM>/m^<NUM> (<NUM> pounds per cubic inch), aluminum has a typical density of <NUM>,<NUM>/m^<NUM> (<NUM> lbs. /in^<NUM>), titanium has a typical density of <NUM>,<NUM>/m^<NUM> (<NUM> lbs. /in^<NUM>), and composites can have densities ranging from less than <NUM>,<NUM>/m^<NUM> (<NUM> lbs. /in^<NUM>) to more than <NUM>,<NUM>/m^<NUM> (<NUM> lbs. /in^<NUM>).

Other properties may also be of interest, including properties related to the ability or tendency for such materials to convert vibrational movement to heat, thereby wasting or dissipating energy that could otherwise be used to advance the well. For example the internal friction and damping capacity of the material may be considered in the selection.

Regarding the specific materials that may be used, presently contemplated tubulars may be selected from aluminum tubulars, for example, from <NUM>, <NUM>, and <NUM> series alloys, while titanium tubulars may be selected from so-called Alpha, Alpha-Beta and Beta alloy families. Suitable composites may include carbon fiber compositions or metal matrix alloys. As noted above, ductile iron products may also be usefully employed.

Claim 1:
A drill string (<NUM>) to be advanced in a well by a torque applied from a rig floor (<NUM>), the drill string (<NUM>) comprising:
a drill bit (<NUM>);
a bottom hole assembly (<NUM>) adjacent to the drill bit (<NUM>);
an extended string assembly (<NUM>, <NUM>'; <NUM>, <NUM>') adjacent to the bottom hole assembly (<NUM>) opposite to the drill bit (<NUM>), comprising a plurality of tubular products, each tubular product comprising a pipe section (<NUM>) with screw connectors (<NUM>) at each end, the plurality of tubular products being connected to each other to form the extended string;
wherein a first set of the plurality of tubular products is made of vibration damping material, and wherein a second set of the plurality of tubular products is made of a different material less able to dampen vibration experienced by the drill string during drilling,
wherein a plurality of vibration damping drill pipe sections (<NUM>, <NUM>') is formed, each vibration damping drill pipe section (<NUM>, <NUM>') being formed from a plurality of tubular products from the first set of tubular products, and
wherein a plurality of further drill pipe sections (<NUM>, <NUM>') is formed, each further drill pipe section (<NUM>, <NUM>') being formed from a plurality of tubular products from the second set of tubular products,
wherein the plurality of vibration damping drill pipe sections (<NUM>, <NUM>') and the plurality of further drill pipe sections (<NUM>, <NUM>') are alternately arranged starting with a first one of the plurality of vibration damping drill pipe sections (<NUM>, <NUM>') provided near or adjacent to the bottom hole assembly (<NUM>), and
wherein the plurality of vibration damping drill pipe section (<NUM>, <NUM>') has a length of less than about <NUM>% of the overall length of the drill string (<NUM>).