Boring or penetrating the earth – With bit wear signal generating
Reexamination Certificate
2002-08-09
2004-11-09
Schoeppel, Roger (Department: 3672)
Boring or penetrating the earth
With bit wear signal generating
C175S050000, C175S041000, C324S338000, C073S152050, C250S254000
Reexamination Certificate
active
06814162
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates generally to single roller cone drill bits for drilling boreholes in earth formations. More specifically, the invention relates to a single cone bit with interchangeable cutting structures, a box-end connection, and integral sensory devices for evaluation of the formation and bit health.
2. Background Art
One aspect of drilling technology relates to roller cone drill bits are used to drill boreholes in earth formations. The most common type of roller cone drill bit is a three-cone bit, with three roller cones attached at the end of the drill bit. When drilling smaller boreholes with smaller bits, the radial bearings in three-cone drill bits become too small to support the weight on the bit that is required to attain the desired rate of penetration. In those cases, a single cone drill bit is desirable. A single cone drill bit has a larger roller cone than the roller cones on a similarly sized three cone bit. As a result, a single cone bit has bearings that are significantly larger that those on a three cone bit with the same drill diameter.
FIG. 1A
shows a prior art single cone drill bit. The single cone bit
1
includes one roller cone
4
rotatably attached to a bit body
16
such that the cone's drill diameter is concentric with the axis of rotation
6
of the bit
1
. The roller cone
4
has a hemispherical shape and typically drills out a bowl shaped bottom hole geometry. The drill bit
1
includes a threaded connection
14
that enables the drill bit
1
to be connected to a drill string (not shown). The male connection shown in
FIG. 1A
is also called a “pin” connection. A typical single cone bit is disclosed in U.S. Pat. No. 6,167,975, issued to Estes.
FIG. 1B
shows a cross section of a prior art drill bit
1
drilling a bore hole
3
in an earth formation
2
. The roller cone
4
is rotatably mounted on a journal
5
that is connected to the bit body
16
.
Another aspect of drilling technology involves formation evaluation using sensors that detect the properties of the formation, such as resistivity, porosity, and bulk density. Formation evaluation allows a well operator to know the properties of the formation at various depths so that the well can be developed in the most economical way. Three of the sensors known in the art that are used for formation include button resistivity sensors, density logging sensors, and neutron logging sensors, each of which will now be described.
A button resistivity tool includes a number of electrode buttons, for example three buttons, that are placed into contact with the borehole wall. One of the buttons injects an electrical current into the formation, and the potential difference is measured between the other two buttons. The potential difference is related to the resistivity of the formation. Button resistivity tools are described with more detail below in the discussion of measurement-while-drilling applications.
A density logging tool uses back scattered radiation to determine the density of a formation. A typical density logging tool is described in U.S. Pat. No. 4,048,495, issued to Ellis, and is shown in FIG.
2
. The density logging tool
20
is shown disposed in a borehole
3
on a wireline
10
. The tool
20
includes a caliper
5
that positions the tool
20
so that the source
24
and sensors
21
,
22
of the tool
20
are pressed into the mud-cake layer
23
, as close as possible to the borehole wall
12
.
The density logging tool
20
contains a gamma ray source
24
, typically Cesium-137, that emits medium energy gamma rays into the formation. The source
24
is enclosed in shielding
26
that shields the detectors
21
,
22
from gamma rays coming directly from the source
24
. The front face
29
of the tool includes a window
25
that enables a collimated beam of gamma rays to be transmitted into the formation
2
. Through a process called “Compton scattering,” the gamma rays scatter back into the borehole and into the detectors
21
,
22
.
Compton scattering is the interaction of a gamma ray with electrons. When a gamma ray interacts with an electron, it imparts part of its energy to the electron, and the gamma ray changes direction. Through one or more Compton scattering events, gamma rays can be scattered back into the borehole. The number of scattering events that occur depends on the density of electrons in the material into which the gamma rays are transmitted. Because the density of electrons depends on the density of the material, a density logging tool can measure the density of a formation by measuring the number of gamma rays that are back scattered in the formation and return to the borehole where they can be detected by the tool.
A typical density logging tool
20
contains two gamma ray detectors, a short-spaced detector
22
, and a long-spaced detector
21
. The long-spaced detector
21
is located about 36 cm from the source
24
. Because of the distance between the source and the long-spaced detector
21
, the long-spaced detector receives gamma rays that are mostly scattered deep in the formation
2
. Further, the front face
27
of the density tool has a window
28
over the long-spaced detector
21
. The window
28
is shaped to collimate the gamma rays so that those gamma rays that are received in the detector
21
are even more likely to have scattered relatively deep in the formation
2
and not the mud-cake layer
23
. Even with the location of the long-spaced detector
21
and the collimating window
28
, the density computed by the long-spaced detector
21
is still affected by the density of the mud-cake layer
23
, which the gamma rays must pass through twice. Thus, the density value computed from the long-spaced detector
21
is strongly affected by the density of the mud-cake layer
23
.
The density measured by the long-spaced detector
21
can be corrected using the short-spaced detector
22
, which is typically located about 11 cm from the source. The short-spaced detector
22
receives back scattered gamma rays that have scattered in materials close to the borehole wall
3
, like the mud-cake layer
23
. Again, a window
29
in the front face
27
of the tool
20
collimates the incoming gamma rays so as to increase the chance that detected gamma rays were scattered in the mud-cake layer
23
. By combining the measurements of the two detectors
21
and
22
, a corrected value for the formation density can be computed, as is known in the art.
A neutron logging tool makes a measurement corresponding to the porosity of a formation. A typical neutron logging tool is disclosed in U.S. Pat. No. 4,035,639 issued to Boutemy et al. A neutron logging tool contains a neutron source, typically an Americium-Beryllium source, and a neutron detector. The source emits high energy neutrons, also called “fast” neutrons, into the formation. The fast neutrons lose energy as they collide with atoms in the formation, eventually becoming slow neutrons, also called “thermal” neutrons. Thermal neutrons will randomly migrate in the formation. Some of the migrating thermal neutrons will migrate back into the borehole. A neutron logging tool detects the thermal neutrons that randomly migrate back into the borehole.
Hydrogen atoms, with an atomic number of one, have approximately the same mass as a neutron. Because of their similar mass, a neutron loses much more energy in collisions with hydrogen atoms than it does in collisions with any other atom. Thus, the rate at which fast neutrons become thermal is related to the number of hydrogen atoms in the moderating material. As a result, the number of thermal neutrons detected by the neutron logging tool is related to the number of hydrogen atoms in the formation. Because water and hydrocarbons have a similar amount of hydrogen atoms, the neutron logging tool measures how much of the formation is occupied by water and hydrocarbons. In non-gas bearing formations, a measurement from a neutron logging tool is related to the formation's porosity.
FIG. 3
shows a wireline neutron l
Moran David P.
Witman, IV George B.
Osha & May L.L.P.
Schoeppel Roger
Smith International Inc.
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