Boring or penetrating the earth – Automatic control – Of boring means including a below-ground drive prime mover
Reexamination Certificate
2000-09-25
2002-04-16
Tsay, Frank S. (Department: 3672)
Boring or penetrating the earth
Automatic control
Of boring means including a below-ground drive prime mover
C175S062000, C175S081000
Reexamination Certificate
active
06371221
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides an improved coring bit motor and a method for obtaining a material core sample from the side wall of a drilled well.
BACKGROUND OF THE RELATED ART
Wells are generally drilled into the earth's crust to recover natural deposits of hydrocarbons and other desirable and naturally occurring materials trapped in geological formations. A slender well is drilled into the ground and directed to the targeted geological location from a drilling rig at the surface. In conventional “rotary drilling” operations, the drilling rig rotates a drillstring comprised of tubular joints of steel drill pipe connected together to turn a bottom hole assembly (BHA) and a drill bit that are connected to the lower end of the drillstring. During drilling operations, a drilling fluid, commonly referred to as drilling mud, is pumped and circulated down the interior of the drillpipe, through the BHA and the drill bit, and back to the surface in the annulus.
Coring is generally a process of removing an inner portion of a material by cutting with an instrument. While some softer materials may be cored by forcing a coring sleeve translationally into the material, for example soil or an apple, harder materials generally require cutting with rotary coring bits; that is, hollow cylindrical bits with cutting teeth disposed about the circumferential cutting end of the bit. The cored material is generally captured within the coring apparatus for retrieval from the well bore. Coring is typically used to remove unwanted portions of a material or to obtain a representative sample of the material for analysis to obtain information about its physical properties. Coring is extensively used to determine the physical properties of downhole geologic formations encountered in mineral or petroleum exploration and development.
Conventional coring of wells drilled to recover naturally occurring hydrocarbons is performed using a coring bit and core barrel attached to the end of the drill string. The core is captured inside the core barrel as the rotating coring bit penetrates the formation of interest. This coring process substantially disrupts the normal drilling process because the drill bit has to be removed from the end of the drill string and replaced with a coring bit. Coring in this manner can be very time consuming and costly. However, this method usually provides for a high rate of success for obtaining core samples for all of the formation drilled through in this manner.
Conventlonal side wall rotary coring is characterized by the use of a coring bit with a hollow, cylindrical configuration and cutting teeth embedded about the circumference of one open end. The coring bit is generally rotated about its axis as it is forced against the side wall of the well. As a core sample is cut from the side wall, the core sample is received into the hollow barrel defined by the interior walls of the coring bit. The optimal speed of rotation of the coring bit and the optimal weight on bit (the magnitude of the axial force urging the bit into the side wall) are generally determined by the type of formation being cored and by the physical characteristics of the coring bit.
Petroleum and other naturally occurring deposits of minerals or gas often reside in porous geologic formations deep in the Earth's crust. A formation of interest in a drilled well can be investigated using a coring tool to obtain representative samples of rock taken from the wall of the well adjacent to the formation of interest. The representative rock sample is generally cored from the formation using a hollow, cylindrical coring bit. Rock samples obtained through side wall coring are generally referred to as “core samples.” Core samples are physically removed from the wall of the well and retrieved within the coring tool to be transported to the surface.
Analysis and study of core samples enables engineers and geologists to assess important formation parameters such as the reservoir storage capacity (porosity), the flow potential (permeability) of the rock that makes up the formation, the composition of the recoverable hydrocarbons or minerals that reside in the formation, and the irreducible water saturation level of the rock. These estimates are crucial to subsequent design and implementation of the well completion program that enables production of selected formations and zones that are determined to be economically attractive based on the data obtained from the core sample.
Several coring tools and methods of obtaining core samples have been used for conventional side wall coring. There are generally two types of coring methods and apparatus, namely rotary coring and percussion coring. The present invention is directed towards rotary coring, the more preferred method because of the quality of the core sample obtained.
Rotary coring of side walls generally involves forcing an open and exposed circumferential cutting end of a hollow cylindrical coring bit against the wall of the well and rotating the coring bit to promote cutting at the leading end. The coring tool is secured against the wall of the well at the zone or formation of interest with the rotary core bit oriented towards the wall of the well. The coring bit is deployed radially outwardly away from the coring tool axis and toward the wall of the well.
The coring bit is generally coupled to a coring motor through an extendable shaft or mechanical linkage. The shaft or linkage advances the rotating coring bit axially towards the side wall to bring the cutting end of the coring bit into contact with the side wall. The coring bit penetrates into the side wall by removing rock within a cylindrical cutting zone. The circumferential cutting end of the coring bit has a plurality of teeth and is often embedded with carbides, diamonds or other materials with superior hardness for cutting rock.
A cylindrically-shaped core sample is received into the hollow interior of the coring bit as cutting of the core sample progresses. After a core sample of the desired length is received, the core sample is broken free from the formation rock by breaking the remaining connection (radial cross-section) within the open, cutting end of the coring bit. The core bit and the core sample within it are retrieved into the coring tool by retracting the shaft or linkage used to extend the coring bit to its deployed position. The retrieved core sample may be ejected from the coring bit within the coring tool to allow use of the coring bit for obtaining subsequent samples at the same or different depths.
Rotary coring is the preferred method of obtaining a core sample because the core sample retains its flow and storage properties without the fracturing and compaction involved in percussion coring. However, efficient rotary coring requires efficient use of limited space. Because of the number of components and the physical manipulations required to recover a conventional side wall core sample, conventional rotary side wall coring presents many challenges associated with the limited space available downhole. As wells are successfully being drilled to deeper formations, and as directional wellbores reach further and further from the true vertical location of the surface location, these wells necessarily become more slender, thereby providing less space for positioning, deploying and operating conventional coring devices.
While it is favorable to obtain as large a representative sample as can be had from the side wall, there are physical limitations that make obtaining a larger core sample difficult and costly. The length of the core sample is limited by the stroke or travel of the coring bit. That is, from the time the cutting teeth of the coring bit initially touch the side wall, the maximum axial displacement into the side wall is determined by the mechanical characteristics of the coring tool.
The mechanical configuration of prior art coring tools is dictated by several different parameters. For cutting, the rotary coring bit must be rotated on its axis using some portable s
Contreras Gary W.
Harrigan Edward
Hill Bunker M.
Lauppe Dean W.
Sundquist Robert W.
Christian Steven L.
Ryberg John J.
Salazar Jennie (JL)
Schlumberger Technology Corporation
Tsay Frank S.
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