US20070261886A1 - Core drill assembly with adjustable total flow area and restricted flow between outer and inner barrel assemblies - Google Patents

Abstract

A core drill assembly with replaceable fluid nozzles permitting effective total flow area adjustment (TFA), substantial optimization of hydraulic force at the cutting face to improve rate of penetration (ROP) and core quality. At least one seal assembly to restrict drilling fluid flow while permitting mutual rotation between the core head ID and the lower shoe is disposed in an annulus defined therebetween.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/800,620, filed May 15, 2006, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
• Embodiments of the present invention are related to a core drill assembly with adjustable drill fluid total flow area and, more particularly, to a core drill assembly which includes replaceable cutting fluid nozzles and a seal assembly disposed between adjacent portions of the outer barrel assembly and the inner barrel assembly, as well as to methods of coring.
BACKGROUND
• Current core head designs use a fixed total flow area (TFA) to circulate drilling fluid through the core head, also known as a core bit, during down-hole coring operations. The TFA is a calculated discharge area for the drilling fluid which may include an annulus ID gauge fluid course between the core head ID and the exterior of the lower shoe, carried by the inner barrel assembly, or core head face discharge ports, or a combination of the two. Drilling fluid is circulated through the ID fluid courses and the face discharge ports to cool and clean cutting structure carried on the face of the core head, and to remove cuttings generated when the cutting head penetrates the formation being cored. The hydraulic force, or the ability of the drilling fluid to removing material cuttings from the cutting head face, is measured in hydraulic horsepower/in²(HSI) and is an indicator of drilling fluid cleaning efficiency. If the hydraulic force is too low, there will be poor cleaning of the cutting structure and cuttings will interfere with the rate of penetration (ROP) in forming the bore hole. If the hydraulic force is too high, there may be erosion of the bole hole, which can result in a stuck drill string, and the drilling fluid may contaminate the core sample. By using HSI and ROP measurements, the optimum amount of hydraulic force can be designed into a core drill assembly.
• FIG. 1 is a cross-section of a conventionalcore drill assembly10, with a non-adjustable TFA or drilling fluid flow area defined by the areas of theannulus50 and thedischarge ports30. Theannulus50 is the gap between the ID ofcore head14 and the outside of thelower shoe18. With this arrangement, drilling fluid is pumped down the drill string, tocore drill assembly10, where a portion of the drilling fluid will travel through theannulus50 and exit thecore drill assembly10 proximate the leading edge of thelower shoe18, while the remaining drilling fluid enters thefluid course20 withincore head14, and exits thedischarge ports30 located on theface16 ofcore head14, as respectively shown by the arrows inFIG. 1l The drilling fluid is used to cool thecutters60 and flush cuttings away from theface16 ofcore head14. However, since the TFA is non-adjustable, the operator cannot optimize the amount of drilling fluid at thedrill face16 ofcore head14 and the HSI.
• With the non-adjustable TFA of current core head designs, the only variable is the circulation rate of the drilling fluid, and therefore, the HSI cannot be optimized. Also, in current core heads there is always some drilling fluid flow through the annular space between the core head ID and the lower shoe. In core heads using ID fluid courses only, all of the flow travels through the annulus whereas, when core head face discharge ports are used in combination with the annulus, it is difficult to determine amount of drilling fluid “split” between the discharge ports and the annulus. The difficulty arises because the actual annulus gap spacing between the core head ID and the lower shoe is not known when the core head is down hole. The annulus gap is nominally ⅜ inch to ½ inch ; however, when using an aluminum or fiberglass inner tube, in the inner barrel assembly, gaps up to 5½ inches may be required in order to compensate for the different rates of thermal expansion attributed to the materials of the inner tube and the core head. Under bottom-hole temperature, the gap may decrease to the estimated desirable gap of ⅜ inch to ½ inch, but uncertainty about the actual and estimated bottom-hole temperature, can result in a significant error in spacing adjustment. As the area of the annulus gap is added directly into the TFA calculation, the uncertainty of the gap size makes accurately calculating TFA difficult. The split of flow between the annulus between the OD of the inner tube shoe and the ID of the core head, and the face discharge ports is dependent upon their relative TFA. Depending upon actual spacing down hole, the annular TFA could be higher than the TFA of the face discharge ports, with the result that most of the flow of drilling fluid will pass through the ID annulus. This significantly reduces the effectiveness of the face discharge ports, and reduces further the HSI delivered to the cutting structure of the core head. Adjusting the TFA of the face discharge ports in this case would not increase HSI, since the bypass flow would simply be increased through the ID annulus. To increase HSI, the bypass flow through the ID annulus must be sealed off, or severely restricted, to divert as much of the flow as possible to the face discharge ports, or nozzles.
• For a conventional drill bit with replaceable nozzles, the TFA can be optimized by utilizing different diameter nozzles in the discharge ports. However, in a conventional core drill assembly, since at least some of the drilling fluid flow travels through the annulus, a change of discharge port size will change the resistance at the nozzles and will proportionally change the amount of drilling fluid bypassing through the annulus. This problem is highlighted when looking at the performance of the drill bit versus a core drill. A drill bit will normally operate in the range of 4-8 HSI, whereas an 8½ inch by 4 inch core drill may operate as low as 0.2 HSI.
• In view of the shortcomings in the art, it would be advantageous to provide a core drill with adjustable TFA, by fitting the core head with replaceable nozzles and sealing off the annulus between the core head ID and the lower shoe. This will allow an operator to apply the same drilling optimization concepts to coring as used with conventional drilling, and allow the HSI to be improved over conventional core head designs, with corresponding improvements in coring performance, ROP and core quality.
BRIEF SUMMARY OF THE INVENTION
• Embodiments of the invention include replaceable nozzles fitted in at least some of the drilling fluid outlet ports, proximate the face of the core head. The nozzle design will compensate for the smaller surface area of the typical core drill face and new nozzle locations and jet directions are contemplated to take advantage of the improved HSI at the cutting face, including directing nozzles towards interior cutters of the core head in order to clear cuttings and provide cooling.
• In one embodiment of the present invention, the annulus between the cutting head and the lower shoe is substantially sealed with a seal structure, which may be broadly characterized as a seal assembly or a seal element, without substantial rotational interference between the core head and the lower shoe, which would cause the lower shoe and inner tube to turn with the outer barrel assembly and core head.
• One embodiment includes one or more grooves formed into the ID of the core head to accommodate an annular seal similar to an O-ring in each of the grooves. The design of the O-ring or other annular seal allows some drilling fluid flow to bypass under reduced pressure, but under normal operating circumstances the O-ring or other annular seal seals substantially completely.
• In a second embodiment of the present invention, the annulus between the core head and the lower shoe is substantially sealed using split rings made from a material such as nylon or Teflon®. This embodiment includes one or more grooves formed in the ID of the core head where split rings of the appropriate size are installed to seal the annulus. The seals will fit somewhat loosely in the grooves and may rotate during coring operations, but will provide a sufficient seal to enable effective TFA adjustments by installing different sizes of drilling fluid nozzles. The loose fit will reduce friction between the core head ID and the lower shoe, to eliminate any tendency for the lower shoe and inner tube to rotate.
• Other embodiments of the present invention employ one or more of a wiper seal, a chevron seal, a packer cup or a restrictor sleeve disposed between the core head and the lower shoe to substantially restrict fluid flow therebetween while permitting rotational movement of the core head about the lower shoe.
• Embodiments of the present invention also include methods of using a core drill assembly.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
• FIG. 1 is a cross-section of a conventional core drill assembly with an non-adjustable TFA defined by the area of the annulus between the core head and the lower shoe, and the area of the drilling fluid ports.
• FIG. 2 is a cross-section of a core drill assembly with a seal structure between the core head and the lower shoe and replaceable nozzles;
• FIG. 3 is a partial cross-section of a core drill assembly including an O-ring or wiper seal type seal assembly;
• FIG. 4 is a partial cross-section of a core drill assembly including a split-ring type seal assembly;
• FIG. 5 is a partial cross-section of a core drill assembly including a labyrinth seal assembly; and
• FIG. 6 is a partial cross-section of a core drill assembly including a restrictor sleeve.
DETAILED DESCRIPTION
• FIG. 2 schematically depicts acore drill assembly10 of the present invention includingreplaceable nozzles36 at the discharge ends offluid courses20, and at least oneseal assembly40 disposed between thecore head14 and thelower shoe18. These features allow the operator to change the TFA of thecore drill assembly10 and optimize the HSI. The operator can selectreplaceable nozzles36 having a discharge opening34 of an appropriate diameter to adjust TFA. Thus, if a volume of drilling fluid is pumped under pressure, at a substantially constant flow rate, down the drill string,seal assembly40 will divert substantially all of the drilling fluid volume away from theannulus50 and into thefluid courses20 where the drilling fluid will exit through discharge opening34 ofreplaceable nozzles36. The diameters ofdischarge openings34 will affect both the rate of discharge and the velocity of the escaping drilling fluid. Under optimized conditions, as provided by the present invention, the drilling fluid, emanating from thedischarge openings34, will effectively clear cuttings away from theface16 and ofcore head14 and properly coolcutters60. The optimum diameter ofdischarge openings34 for a specific material or formation, and core head or core size, can be determined or predicted by the use of historical data, including ROP measurements. As shown at the left-hand side ofFIG. 2, theseal assembly40 may be partially received in a groove in ID of thecore head14 or, as shown at the right-hand side ofFIG. 2, theseal assembly40 may be partially received in a groove in the exterior of thelower shoe18. Ascore head14 rotates aboutlower shoe18 during a coring operation, fluid flow therebetween will be substantially restricted byseal assembly40, as indicated by the smaller size of the arrows belowannulus50 in comparison to those influid courses20.
• FIGS. 3 and 4, are partial cross-section views ofcore drill assembly10 provided, to show additional detail of several embodiments of the at least oneseal assembly40. The at least oneseal assembly40 is positioned in theannulus50, or the gap defined between the ID ofcore head14 and the outside of thelower shoe18. Theseals42 and44 are installed ingrooves46 formed in the ID ofcore head14. Theseals44 shown inFIG. 3 may comprise an O-ring or other continuous ring type that may have a round or oval cross-section, or may include lips which function as “wipers,” as shown. The material ofseals44 may include, but is not limited to, rubber, neoprene, or polyethylene or a combination thereof. Theseals42 shown inFIG. 4 are of a split-ring design which rides loosely in thegrooves46. Examples of suitable materials for the split-ring seals42 are nylon and Teflon® polymers. The at least oneseal assembly40 will substantially restrict the flow of the drilling fluid pumped down the drill string, forcing the drilling fluid to bypass theannulus50 and into thefluid courses20, traveling in the direction offlow arrows26.
• FIG. 5 is a partial cross-section view of acore drill assembly10 including alabyrinth seal48 having a plurality of radially projecting, axially spaced annular elements separated bylabyrinth slots56. Thelabyrinth seal48 is formed into the structure of one of thecore head14 ID or the exterior surface of thelower shoe18. However, alabyrinth seal48 with mating, interdigitated elements or components as shown in broken lines at E can be formed with the cooperating parts disposed on both thecore head14 ID and thelower shoe18. The total number oflabyrinth slots56 is not specified, and will vary depending on the expected pressure differential between the pumped drilling fluid and drill work face. Thelabyrinth seal48 must have sufficient length and number oflabyrinth slots56 to effectively sealannulus50. Withannulus50 sealed, the drilling fluid will enterfluid courses20, flowing in the direction indicated byflow arrows26.
• It is also contemplated that the seals may be carried on the exterior of thelower shoe18 instead of oncore head14, or may be carried on both components. It is also contemplated that a seal comprising an upwardly facing packer cup with a frustoconical elastomeric skirt may be utilized in addition to, or in lieu of, other seal configurations. Chevron-type seals, as well as metallic or elastomeric seal back-up components, may also be employed.
• FIG. 6 depicts yet another embodiment of the present invention, wherein a seal element in the form ofrestrictor sleeve64 is disposed on anannular shoulder62 machined or otherwise formed on the ID of thecore head14, and retained therein through the use of an appropriate bonding agent, such as BAKERLOK® compound, available from various operating units of Baker Hughes Incorporated, assignee of the present invention. As with the previous embodiments,discharge openings34 ofreplaceable nozzles36 may be selected for optimum TFA. A conventionallower shoe18 is run inside ofcore head14, and extends longitudinally therethrough. The outer surface (shown in broken lines for clarity) oflower shoe18 is in close proximity to the ID ofrestrictor sleeve64, so that a very small clearance radial clearance C, for example about 1 mm, is achieved This small, annular clearance C betweenlower shoe18 andrestrictor sleeve64, while permitting rotation oflower shoe18 andrestrictor sleeve64 aboutlower shoe18, will substantially restrict the flow of the drilling fluid pumped down the drill string, forcing the drilling fluid to bypass theannulus50 and into thefluid courses20 to exit throughdischarge openings34 ofreplaceable nozzles36.
• While the present invention has been depicted and described with reference to certain embodiments, the invention is not so limited. Additions and modifications to, and deletions from, the described embodiments will be readily apparent to those of ordinary skill in the art. The present invention is, thus, limited only by the claims which follow, and equivalents thereof.

Claims (13)

1. A core drill assembly comprising:

a core head including an inside diameter, a face, and at least one fluid course having an outlet on the face;

a lower shoe;

at least one replaceable nozzle disposed in the at least one fluid course proximate the outlet; and

at least one seal structure, configured to permit rotation between the core head and lower shoe assembly, disposed between the core head inside diameter and an exterior surface of the lower shoe.

2. The assembly ofclaim 1, wherein the at least one replaceable nozzle is replaceable with another replaceable nozzle having a different inner diameter.

3. The assembly ofclaim 1, wherein the at least one seal structure comprises a seal assembly and includes at least one groove formed on at least one of the inside diameter of the core head and the exterior surface of the lower shoe.

4. The assembly ofclaim 3, wherein the at least one seal assembly includes at least one seal element carried in the at least one groove.

5. The assembly ofclaim 4, wherein the at least one seal element is at least one of an o-ring seal, a wiper seal, a split-ring seal, a chevron seal or a packer cup.

6. The assembly ofclaim 4, wherein the at least one seal element is made of at least one of a nylon, a Teflon®, a polyethylene, a rubber or a neoprene material.

7. The assembly ofclaim 1, wherein the at least one seal structure comprises a labyrinth seal.

8. The assembly ofclaim 1, wherein the at least one seal structure comprises a restrictor sleeve disposed within the core head laterally adjacent an exterior surface of the lower shoe.

9. The assembly ofclaim 8, wherein the restrictor sleeve rests on an annular shoulder on the ID of the core head.

10. The assembly ofclaim 8, wherein an ID of the restrictor sleeve and the laterally adjacent exterior surface of the lower shoe are mutually spaced by about 1 mm.

11. A method for substantially controlling the total flow area (TFA) of a core drill assembly comprising:

providing a core head including at least one fluid course having an outlet on the face thereof;

installing a replaceable nozzle having a selected inner diameter in the fluid course proximate the outlet;

disposing a lower shoe at least partially within the core head; and

rotating the core head about the lower shoe while substantially preventing a flow of drilling fluid between the core head and the lower shoe and directing flow through the at least one replaceable nozzle.

12. The method ofclaim 11, further including replacing the at least one replaceable nozzle with another replaceable nozzle having a different inner diameter.

13. The method ofclaim 11, further comprising providing an absolute fluid seal between the core head and the lower shoe.

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