Patent Application
20090260878
The present invention relates generally to well drilling operations and, more particularly, to well drilling operations using magnetic ranging to drill wells in specified orientations with respect one another, wherein the wells may include wells to be completed open hole and/or wells to be completed with equipment disposed therein and hindering access to the wellbore.
It is often desirable to position wells close together. For example, in certain oilfield applications, drilling wells close together may facilitate extraction of heavy oil. Indeed, heavy oil is generally too viscous in its natural state to be produced from a conventional well. Accordingly, to produce heavy oil, multiple wells, such as a pair of Steam Assisted Gravity Drainage (SAGD) wells, may be employed. A SAGD well pair typically includes two substantially parallel horizontal wells that are positioned relatively close together in a stacked orientation, and that use superheated steam to heat heavy oil until its viscosity is low enough to be produced. The upper well in a SAGD well pair may be referred to as an injector well. The lower well in a SAGD well pair may be referred to as a producer well. In operation, the injector well typically injects superheated steam into a heavy oil zone formation, creating a steam chamber to heat the heavy oil contained therewithin. When the heated heavy oil becomes less viscous, gravity pulls the oil into the producer well, which facilitates extraction of the oil.
When wells are drilled close to one another, there are typically spacing requirements that are essentially impossible to meet using conventional surveying techniques. For example, in a SAGD well pair, it may be desirable for the injector well and the producer well to be drilled such that they maintain a target separation distance, such as an approximately constant vertical separation distance (e.g., 4 to 6 m) over a horizontal distance (e.g., 500 m to 1500 m). Conventional measurement while drilling (MWD) survey data, which may only include inclination and azimuth data, does not provide sufficient accuracy to maintain a consistent separation distance between the injector well and the producer well. Accordingly, conventional spacing techniques may employ conventional magnetic ranging to facilitate drilling two or more wells within a specified distance from each other. For example, such conventional magnetic ranging techniques may be utilized to drill the second of the two wells of a SAGD well pair in an appropriate location with respect to the first well.
Conventional magnetic ranging techniques involve placing wireline equipment in a first well while a second well is drilled a specified distance from the first well. In operation, a magnetic field between the wireline equipment in the first well and a drilling bottom hole assembly (BHA) in the second well may enable the BHA in the second well to maintain an accurate vertical separation distance between the first and second wells of the SAGD pair. For example, the wireline equipment may include a solenoid configured to generate a known magnetic field, as is done with a Magnetic Guidance Tool (MGT), and the field may be detected to facilitate guiding the BHA. In another example, a wireline magnetometer may be used to measure a magnetic field generated by permanent magnets in the BHA of the second well, as is done with Rotating Magnet Ranging (RMR) systems, to facilitate guiding the BHA. However, when the wells are horizontal, these conventional magnetic ranging techniques require a wireline tractor to push the wireline tool down the length of the first horizontal well as the second well is being drilled. This can be an expensive procedure in a typical cased-hole tractor operation. Further, such a procedure may be even more difficult, expensive, and risky for an openhole tractor operation.
Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
In accordance with one embodiment, a method of drilling a well includes leaving a drill string in position within a primary well, and drilling a secondary well using the drill string as a target for magnetic ranging while drilling such that the secondary well is positioned with a specified orientation relative to the drill string.
Advantages of embodiments of the invention may become apparent upon reading the following detailed description and upon reference to the drawings in which:
One or more specific embodiments of the present invention are described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
In well drilling operations, it may be desirable to place wells close together or in specific orientations relative to one another. Indeed, in SAGD operations, for example, well pairs are generally positioned parallel and close together to facilitate production of heavy oil. Additionally, it may be desirable in other drilling operations to position a series of wells in a specific orientation relative to one another. For example, it may be desirable to drill a number of parallel wells in a row. Well drilling operations, such as SAGD operations and the like, typically have a criterion for spacing that requires the use of some type of ranging technique, other than conventional MWD surveying techniques that only report inclination and azimuth, to establish orientations and distances between the wells. It is now recognized that the ability to perform such ranging techniques may become an issue when a well is completed openhole or with equipment positioned in the well that prevents wireline equipment from accessing the well.
Embodiments of the present invention are directed to systems and methods for drilling two or more wells while maintaining a positional relationship between the wells, such as a specific angular orientation of less than 90 degrees or a distance of a few meters between the walls of each well. In particular, present embodiments are directed to drilling two or more respectively positioned wells that are to be completed openhole (i.e., without casing or liner), or that are to be completed with equipment positioned therein that prevents other equipment from being present in the wellbore. With regard to openhole completions, present embodiments may avoid difficulties associated with properly positioning wireline equipment within a well that does not include casing. For example, by providing a magnetic ranging technique that avoids the use of wireline equipment, present embodiments may avoid undesirable operations that may involve the use of wireline tractors in horizontal, openhole wells. Further, with regard to wells completed with equipment disposed therein, present embodiments may avoid accessibility issues associated with such wells. For example, heating elements (e.g., electrical wires or resistive elements) disposed in a completed well may prevent wireline equipment, such as a wireline tractor, from accessing the wellbore. Present embodiments may avoid such accessibility issues by facilitating magnetic ranging while drilling without requiring the positioning of a wireline specifically for ranging purposes in the wellbore.
The technique referred to as “magnetic ranging while drilling” relates to drilling two or more wells in positions or orientations relative to one another in accordance with present embodiments. Specifically, magnetic ranging while drilling facilitates drilling a well in a specific orientation with respect to a previously drilled well without requiring the use of a wireline tool specifically designed for such a purpose. Though an overview of magnetic ranging while drilling is discussed below, a detailed description of magnetic ranging while drilling is available in published application US 2007/012426 A1, which is incorporated herein by reference.
Turning to the specific features illustrated in
In accordance with one embodiment of the invention, either the first well 12 or the second well 14 is initially drilled and the well drilled subsequently is positioned based on the existing well. For example, the first well 12 may be drilled first, and present embodiments may facilitate drilling the second well 14 in a controlled orientation relative to the first well 12. In some embodiments, multiple wells may be drilled simultaneously with one well acting as the guide. For example, once a portion of the first well 12 has been drilled, the second well 14 may be drilled relative to the position of the first well 12.
As illustrated in
In the illustrated embodiment, the BHA 26 for each set of drilling equipment 20, 22 is equipped to perform magnetic ranging while drilling. In other embodiments only one of the sets of drilling equipment 20, 22 (the set for the subsequently drilled well) may be configured to perform magnetic ranging while drilling. Specifically, in the illustrated embodiment, the BHA 26 includes a drill bit 28 for drilling through the formation 16 and a steerable system 30 to set the direction of the drill bit 28. Further, the BHA 26 includes an electric current driving tool 32, which may be a component of a measurement while drilling (MWD) tool or a standalone tool, such as Schlumberger's E-Pulse or E-Pulse Express tool. The electric current driving tool 32 provides an electric current to an outer drill collar 34 of the BHA 26. The outer drill collar 34 is separated from the rest of the drill pipe 24 by an insulated gap 36 in the drill collar, through which electric current may not pass. The BHA 26 additionally includes a magnetometer tool 38 having a three-axis magnetometer 40. The three-axis magnetometer 40 plays an integral role in the technique known as magnetic ranging while drilling. It should be noted that the BHA 26 may also include logging while drilling (LWD) tools, telemetry tools, and/or other downhole tools for use in a drilling environment.
As depicted in
If the first well 12 were completed with casing, the casing could be utilized to produce a magnetic field as part of performing the magnetic ranging while drilling technique, as discussed in published application US 2007/012426 A1. However, because the first well 12 has been completed openhole, there is no conductive casing in the first well 12 to utilize as a guide for drilling the second well 14. Nevertheless, magnetic ranging while drilling may still be utilized to position the second well 14 with respect to the first well 12 in accordance with present embodiments. Indeed, assuming that the formation 16 is sufficiently strong, as is usually true for openhole completions, equipment may be left in the wellbore of the first well 12 for a time without the risk of the formation collapsing and trapping the equipment. Therefore, in accordance with present embodiments, the drill string 20 may be left in the first well 12 for a time after drilling the first well 12. While leaving equipment in the first well 12 for a prolonged period may require careful monitoring of the formation and proper mud weight, it may be left in position while the second well 14 is drilled. Thus, the drill string 20, which could include drill pipe or coiled tubing, may be utilized to provide a highly conductive target for electrical current. Indeed, the drill string 20 left in the first well 12 may provide a good target for magnetic ranging while drilling to facilitate drilling the second well 14 in a position relative to the position of the first well 12.
Present embodiments involve drilling an initial well (e.g., the first well 12) to a desired or target depth, and then leaving the drill string (e.g., the drill string 20) utilized to drill the initial well in place while one or more additional wells (e.g., the second well 14) are drilled relative to the initial well using magnetic ranging while drilling. Turning to
To ascertain a vertical separation distance from the first well 12 using magnetic ranging while drilling, the electric current driving tool 32 first provides an electric current 50 to the outer drill collar 34. The current 50 produced by the electric current driving tool 32 may, for example, have a frequency between about 1 Hz and about 100 Hz, and may have an amplitude of around 17 amps. Beginning along the outer drill collar 34 of the BHA 26, the current 50 may subsequently enter the heavy oil zone formation 18. The portion of the current 50 that enters the heavy oil zone formation 18 is depicted as an electric current 52.
The drill string 20 positioned in the first well 12 (typically along with drilling mud) provides very low resistance to electricity as compared to the heavy oil zone formation 18, being typically six orders of magnitude lower than the resistance of the heavy oil zone formation 18. As a result, a substantial portion of the current 52 will pass along the drill string 20, depicted as a current 54, rather than travel elsewhere through the heavy oil zone formation 18. The current 54 travels along the drill string 20 before re-entering the heavy oil zone formation 18 as current 56 on its way toward completing the circuit beginning at the electric current driving tool 32, located on the opposite side of the insulated gap 36 from the start of current 50.
The movement of the current 54 along the drill string 20 creates a magnetic field 60, an azimuthal magnetic field centered on the drill string 20. The three-axis magnetometer 40 of the magnetometer tool 38 may detect both the magnitude and the direction of the magnetic field 60 along three axes. The magnitude and direction of the magnetic field 60 may be used to estimate the direction and distance of the BHA 26 in the second well 14 relative to the first well 12. Having determined the estimated direction and distance from the first well 12, the BHA 26 may be controlled using this information to drill the second well 14 at an approximately constant separation distance 62 from the first well 12. For example, the precision available with magnetic ranging while drilling may permit the approximately constant separation distance 62 to approach five meters (5 m) with a variance of approximately one meter (1 m).
The well drilling operation 10 represented in
In the drilling operation illustrated in
Several wells may be ranged from a single well in accordance with present embodiments. For example, multiple wells may be drilled in a circular pattern around an initial well with a drill string residing therein. Additionally, in some cases, it may be desirable to drill wells close enough together such that several wells in a particular direction with respect to an initial well may be ranged from the initial well.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
