Casing and liner drilling bits

A casing bit for drilling a casing section into a subterranean formation, comprising:

• an inner profile, at least a portion of the inner profile having a geometry configured to substantially match a geometry of at least a portion of a drilling profile of a leading face of another drilling tool for subsequently drilling through a portion of the casing bit;
• an outer profile;
• a nose portion;
• at least one aperture formed in the nose portion and configured for delivering drilling fluid from an interior of the casing bit to an exterior thereof;
• a plurality of discrete cutting element retention structures extending from the nose portion, each discrete cutting element retention structure being configured to carry a sole cutting element;
• and
• at least one gage section, the at least one gage section extending longitudinally from adjacent the nose portion.

A casing bit for drilling a casing section into a subterranean formation, comprising:

• an inner profile;
• an outer profile;
• a nose portion;
• at least one thread for securing the casing bit to a separate casing section of a casing string;
• at least one aperture formed in the nose portion and configured for delivering drilling fluid from an interior of the casing bit to an exterior thereof;
• a plurality of cutting elements affixed to the nose portion, the plurality of cutting elements configured for causing failure in the formation by contact therewith;
• and
• at least one gage section configured to define an outermost radius of the casing bit, the at least one gage section extending longitudinally from adjacent the nose portion, the at least one gage section configured to extend longitudinally adjacent at least a portion of the separate casing section of the casing string when the separate casing section is secured to the casing bit.

A casing bit for drilling a casing section into a subterranean formation, comprising:

• an inner profile;
• an outer profile;
• a nose portion;
• at least one aperture formed in the nose portion and configured for delivering drilling fluid from an interior of the casing bit to an exterior thereof;
• at least one gage section, the at least one gage section extending longitudinally from adjacent the nose portion;
• a plurality of generally radially extending blades disposed on the nose portion, at least one of the plurality of blades carrying a plurality of cutting elements affixed thereto, the plurality of cutting elements comprising:
• a first plurality of cutting elements configured to initially engage and drill through a first region and to substantially wear away while drilling through the first region;
• and
• a second plurality of cutting elements configured to engage and drill through a second region to be subsequently encountered by the casing bit, at least one cutting element of the second plurality of cutting elements comprising a polycrystalline diamond cutting element and positioned in rotational alignment with at least one cutting element of the first plurality of cutting elements comprising a tungsten carbide cutting element, the at least one cutting element of the second plurality of cutting elements positioned to rotationally follow the at least one cutting element of the first plurality of cutting elements in a groove formed by the at least one cutting element of the first plurality of cutting elements when the casing bit is rotated during a drilling operation.

A casing bit for drilling a casing section into a subterranean formation, comprising:

• an inner profile;
• an outer profile;
• a nose portion;
• at least one aperture formed in the nose portion and configured for delivering drilling fluid from an interior of the casing bit to an exterior thereof;
• at least one gage section, the at least one gage section extending longitudinally from adjacent the nose portion;
• and
• a plurality of generally radially extending blades disposed on the nose portion, at least one of the plurality of blades carrying one or more cutting elements affixed thereto, at least one of the one or more cutting elements being affixed to the at least one of the plurality of blades by electrically disbonding material.

A casing bit for drilling a casing section into a subterranean formation, comprising:

• an inner profile;
• an outer profile;
• a nose portion;
• at least one aperture formed in the nose portion and configured for delivering drilling fluid from an interior of the casing bit to an exterior thereof;
• at least one gage section, the at least one gage section extending longitudinally from adjacent the nose portion;
• and
• a plurality of generally radially extending blades disposed on the nose portion, at least one blade of the plurality of blades carrying one or more cutting elements affixed thereto;
• and
• at least one groove formed in the at least one blade of the plurality of blades, the at least one groove configured to cause the at least one blade to separate into two or more smaller sections when another drilling tool is used to drill through the casing bit, the at least one groove comprising an end surface extending longitudinally into the at least one blade at a location rotationally behind the one or more cutting elements to a floor, the at least one groove extending through the at least one blade to a rotationally trailing longitudinally extending surface of the at least one blade.

A casing bit for drilling a casing section into a subterranean formation, comprising:

• an inner profile;
• an outer profile;
• a nose portion, at least a portion of the nose portion comprising one or more fibers disposed within a matrix material;
• at least one aperture formed in the nose portion and configured for delivering drilling fluid from an interior of the casing bit to an exterior thereof;
• at least one gage section, the at least one gage section extending longitudinally from adjacent the nose portion;
• and
• a plurality of generally radially extending blades disposed on the nose portion, at least one of the plurality of blades carrying one or more cutting elements affixed thereto.

A drilling assembly for drilling a casing section into a subterranean formation, comprising:

• a casing section of a casing string;
• a casing bit secured to an end of the casing section, the casing bit having an inner profile, an outer profile, and a nose portion;
• at least one aperture formed in the nose portion and configured for delivering drilling fluid from an interior of the casing bit to an exterior thereof;
• at least one gage section, the at least one gage section extending longitudinally from adjacent the nose portion;
• a plurality of generally radially extending blades disposed on the nose portion, at least one of the plurality of blades carrying one or more cutting elements affixed thereto;
• and
• at least one of an incendiary agent, an explosive agent, and a reactive chemical in a container affixed to at least one of the casing section and the casing bit, the at least one of an incendiary agent, an explosive agent, and a reactive chemical being configured to render the casing bit more drillable.