Boring or penetrating the earth – Processes – Sampling of earth formations
Reexamination Certificate
2000-11-14
2004-04-13
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Processes
Sampling of earth formations
C175S020000, C175S226000, C175S250000, C175S403000
Reexamination Certificate
active
06719070
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to apparatus and methods for taking core samples of subterranean formations. Specifically, the present invention relates to a sponge core barrel assembly, and methods of using the same, for obtaining a formation core sample while maintaining the structural and chemical integrity of the core sample for subsequent analysis.
2. State of the Art
Formation coring is a well-known process in the oil and gas industry. In conventional coring operations, a core barrel assembly is used to cut a cylindrical core from the subterranean formation and to transport the core to the surface for analysis. Analysis of the core can reveal invaluable data concerning subsurface geological formations and, particularly, hydrocarbon-bearing formations—including parameters such as permeability, porosity, and fluid saturation—that are useful in the exploration for petroleum, gas, and minerals. Such data may also be useful for construction site evaluation and in quarrying operations.
A conventional core barrel assembly typically includes an outer barrel assembly, a core bit, and an inner barrel assembly. Generally, a conventional outer barrel assembly comprises one or more hollow cylindrical sections, or “subs,” which are typically secured end-to-end by threads. Secured to a lower end of the outer barrel assembly is the core bit, which is adapted to cut a cylindrical core and to receive the core in a central opening, or throat. The opposing upper end of the outer barrel assembly is attached to the end of a drill string, which conventionally comprises a plurality of tubular sections that extend to the surface. Disposed within the outer barrel assembly, and configured to receive the core as the core traverses the throat of the core bit and to retain the core for subsequent transportation to the surface, is the inner barrel assembly.
The outer barrel assembly typically includes a swivel assembly disposed proximate an upper end thereof from which the inner barrel assembly is suspended, an upper end of the inner barrel assembly being releasably secured to the swivel assembly. The swivel assembly includes a thrust bearing or bearings enabling the core bit and outer barrel to rotate freely with respect to the inner barrel assembly suspended within. A conventional outer barrel assembly typically includes a safety joint disposed at its upper end proximate the drill string. If the core barrel assembly becomes wedged or jammed in a bore hole during coring, the safety joint enables the inner barrel assembly and core to be removed, while leaving the outer barrel assembly in the bore hole for subsequent retrieval. The outer barrel assembly may also include one or more sections including core barrel stabilizers that reinforce and stabilize the core barrel during coring, thereby reducing bending of the core barrel assembly and wobble of the core bit. A core barrel assembly may further include an outer tube sub having one or more wear ribs that function to reduce contact between the outer barrel assembly and the wall of the wellbore and, hence, wear of the outer barrel.
Conventional core bits are generally comprised of a bit body having a face surface on one end. The opposing end of the core bit is configured, as by threads, for connection to the lower end of the outer barrel assembly. Located at the center of the face surface is the throat, which extends into a hollow cylindrical cavity formed in the bit body. The face surface includes a plurality of cutters arranged in a selected pattern. The pattern of cutters includes at least one outside gage cutter disposed at the periphery of the face surface that determines the diameter of the bore hole drilled in the formation. The pattern of cutters also includes at least one inside gage cutter disposed adjacent and protruding within the diameter of the throat to determine the outside diameter of the core being cut as it enters the throat.
During coring operations, a drilling fluid is usually circulated through the core barrel assembly to lubricate and cool the plurality of cutters disposed on the face surface of the core bit and to remove formation cuttings from the bit face surface to be transported upwardly to the surface through an annulus defined between the drill string and the wall of the bore hole. A typical drilling fluid, or drilling mud, may include a hydrocarbon or water base or fluid carrier in which fine-grained mineral matter is suspended. The core bit usually includes one or more ports or nozzles positioned to deliver drilling fluid to the face surface. Generally, a port includes a port outlet at the face surface in fluid communication with a bore. The bore extends through the bit body and terminates at a port inlet. Each port inlet is in fluid communication with an annular region defined between the outer barrel assembly and the inner barrel assembly. Drilling fluid received from the drill string under pressure is circulated into the annular region, which enables the port inlet of each port to draw drilling fluid from the annular region. Drilling fluid then flows through each bore and discharges at its associated port outlet to lubricate and cool the plurality of cutters on the face surface and to remove formation cuttings as noted above.
Located within the outer barrel assembly, and releasably attached to the swivel assembly, is the inner barrel assembly. The inner barrel assembly includes an inner tube configured for retaining the core and a core shoe disposed at one end thereof adjacent the throat of the core bit. The core shoe is configured to receive the core as it enters the throat and to guide the core into the inner tube. A core catcher may be disposed proximate the core shoe to assist, in conjunction with the core shoe, in guiding the core into the inner tube and also to retain the core within the inner tube. Thus, as the core is cut—by application of weight to the core bit through the outer barrel assembly and drill string in conjunction with rotation of these components—the core will traverse the throat of the core bit to eventually reach the rotationally stationary core shoe, which accepts the core and guides it into the inner tube where the core is retained until transported to the surface for examination.
Disposed proximate the upper end of the inner barrel assembly where the inner barrel assembly joins to the swivel assembly is a pressure relief plug. The pressure relief plug allows drilling fluid to circulate through the inner tube to flush the inner tube and to clean the bottom of the bore hole prior to coring. To commence coring, a drop ball is seated in the pressure relief plug to divert drilling fluid away from the inner tube and into the annular region between the outer and inner barrels. As the core enters the inner tube, the pressure relief plug also functions to relieve pressure within the inner tube.
The discharge of drilling fluid from the port outlets at the face surface of a core bit during a coring operation may result in drilling fluid invasion of the core. Drilling fluid invasion may result from any one of a number of conditions, or a combination thereof. Drilling fluid discharged at the face surface of the core bit may, if not appropriately directed radially outward away from the core, flow towards the core being cut where the drilling fluid can then contact the core. Also, in most conventional core bits, a narrow annulus exists in a region bounded by the inside diameter of the bit body and the outside diameter of the core shoe, this narrow annulus essentially being an extension of the annular region and terminating at an annular gap proximate the entrance to the core shoe near the throat of the core bit. Pressurized drilling fluid circulating in the annular region may, in addition to flowing into the port inlets, flow into the narrow annulus and out through the annular gap to be discharged proximate the throat of the core bit. This drilling fluid entering the narrow annulus and exiting the annular gap proximate the throat of the core bit
Hatloy Hallvard S.
Puymbroeck Luc Van
Stibbe Holger
Wilson Bob T.
Bagnell David
Baker Hughes Incorporated
Gay Jennifer H
TraskBritt
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