Rock bolting techniques for forming an in situ oil shale retort

A method for recovering liquid and gaseous products from an in situ oil shale retort formed in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale formed within upper, lower and side boundaries of the retort, the method comprising the steps of:

• excavating formation from within the retort site for forming at least one void extending generally horizontally across the retort site, leaving at least one zone of unfragmented formation within the retort site adjacent such a void, such a zone of unfragmented formation having a generally horizontal free face of formation adjacent such a void;
• and wherein the horizontal cross-section of the horizontal void is similar to the horizontal cross-section of the fragmented mass being formed within the side boundaries of the retort;
• placing a plurality of rock bolts in unfragmented formation adjacent such a horizontal free face of formation, said rock bolts being placed in an array distributed across essentially the entire horizontal cross-section of the horizontal void which extends to the side boundaries of the retort;
• placing explosive in such a zone of unfragmented formation;
• detonating such explosive for explosively expanding formation within such a zone of unfragmented formation toward the rock bolted horizontal cross-section of the horizontal free face for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort;
• establishing a retorting zone in the fragmented mass;
• introducing a retorting gas to the fragmented mass for sustaining the retorting zone and for advancing the retorting zone through the fragmented mass;
• and
• withdrawing liquid and gaseous products from the fragmented mass on the advancing side of the retorting zone.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale, comprising the steps of:

• excavating formation from within the retort site for forming at least one void extending horizontally across the retort site, leaving a zone of unfragmented formation within the retort site above such a void, such a zone of unfragmented formation providing a roof of unfragmented formation above such a void;
• placing an array of rock bolts in at least a portion of said roof;
• placing explosive in such a zone of unfragmented formation above the roof wherein the burden distance of the explosive to the roof is greater than the depth of penetration of the rock bolts into formation adjacent the roof;
• and
• detonating such explosive for explosively expanding formation from such a zone of unfragmented formation toward the free face provided by the roof, including toward the rock bolted portion of the roof, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale, comprising the steps of:

• excavating formation from within the retort site for forming at least one void extending horizontally across the retort site, leaving a zone of unfragmented formation within the retort site above such a void, such a zone of unfragmented formation providing a roof of unfragmented formation above such a void;
• placing an array of rock bolts in at least a portion of said roof;
• placing explosive in an array of column charges distributed across the horizontal cross section of such a zone of unfragmented formation above the roof, the distance from the ends of the column charges to the roof being greater than the depth of penetration of the rock bolts into formation adjacent the roof;
• and
• detonating such explosive for explosively expanding formation from such a zone of unfragmented formation toward the free face provided by the roof, including toward the rock bolted portion of the roof, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale, comprising the steps of:

• excavating formation from within the retort site for forming at least one void extending generally horizontally across the retort site, leaving at least one zone of unfragmented formation within the retort site adjacent such a void, such a zone of unfragmented formation having a generally horizontal free face of formation adjacent such a void;
• placing an array of rock bolts in unfragmented formation adjacent at least a portion of such a horizontal free face;
• drilling a plurality of generally vertical blasting holes in such a zone of unfragmented formation;
• placing explosive in the blasting holes, such explosive having a burden distance to such a horizontal free face that is greater than the depth of penetration of the rock bolts into such zone of unfragmented formation;
• and
• detonating such explosive for explosively expanding formation within such zone of unfragmented formation, including the rock bolted portion of the unfragmented formation, toward said horizontal free face of formation, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale, comprising the steps of:

• excavating at least one void extending horizontally across the retort site, leaving at least one zone of unfragmented formation within the retort site adjacent such a void, such a zone of unfragmented formation having a generally horizontal free face of formation adjacent such a void, such a void having a horizontal dimension similar to the width of the fragmented mass being formed, such a void being formed in the absence of a roof-supporting pillar;
• placing an array of rock bolts in unfragmented formation adjacent at least a portion of such a horizontal free face of formation;
• placing explosive in such zone of unfragmented formation;
• and
• detonating such explosive for explosively expanding formation within such zone of formation toward said horizontal free face, including toward the rock bolted portion of the free face, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale and having upper, lower and side boundaries, comprising the steps of:

• excavating formation within the boundaries of the retort site for forming at least one void and leaving a zone of unfragmented formation within the boundaries of the retort site adjacent such a void, the unfragmented formation having a free face adjacent such void;
• placing an array of rock bolts in at least a portion of the unfragmented formation adjacent such a free face;
• placing explosive in the zone of unfragmented formation with a burden distance at least three times greater than the depth of penetration of the rock bolts into the zone of unfragmented formation adjacent the free face;
• and
• detonating such explosive for explosively expanding the zone of unfragmented formation toward the free face, including the portion containing the array of rock bolts, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale and having upper, lower and side boundaries, comprising the steps of;

• excavating formation within the boundaries of the retort site for forming at least one void extending generally horizontally across the entire horizontal cross section within the side boundaries of the retort being formed, and leaving a zone of unfragmented formation within the boundaries of the retort site adjacent such a void, the unfragmented formation having a free face adjacent such void;
• placing a sufficient array of rock bolts in at least a portion of the unfragmented formation adjacent such a free face that the void can be excavated without leaving roof-supporting pillars of unfragmented formation within the side boundaries of the retort site;
• placing explosive in the zone of unfragmented formation;
• and
• detonating such explosive for explosively expanding the zone of unfragmented formation toward the free face, including the portion containing the array of rock bolts, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale and having upper, lower and side boundaries, comprising the steps of:

• excavating formation within the boundaries of the retort site for forming at least one void and leaving a zone of unfragmented formation within the boundaries of the retort site adjacent such a void, the unfragmented formation having a free face adjacent such void;
• placing an array of rock bolts in at least a portion of the unfragmented formation adjacent such a free face;
• placing explosive in the zone of unfragmented formation by drilling generally vertical blasting holes in the zone of unfragmented formation and placing column charges of explosive in such blasting holes, the burden distance of such explosive charges being at least three times greater than the depth of penetration of the rock bolts into unfragmented formation adjacent the free face;
• and
• detonating such explosive for explosively expanding the zone of unfragmented formation toward the free face, including the portion containing the array of rock bolts, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale and having upper, lower and side boundaries, comprising the steps of:

• excavating formation within the boundaries of the retort site for forming at least one void and leaving a zone of unfragmented formation within the boundaries of the retort site adjacent such a void, the unfragmented formation having a free face adjacent such void;
• placing an array of rock bolts in at least a portion of the unfragmented formation adjacent such a free face;
• drilling a plurality of blasting holes in such zone of unfragmented formation perpendicular to the free face;
• placing explosive in the blasting holes, such explosive having a burden distance to the free face that is at least three times greater than the depth of penetration of the rock bolts into the zone of unfragmented formation;
• and
• detonating such explosive for explosively expanding the zone of unfragmented formation toward the free face, including the portion containing the array of rock bolts, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

A method for forming an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale and having upper, lower and side boundaries, comprising the steps of:

• excavating formation within the boundaries of the retort site for forming at least one void and leaving a zone of unfragmented formation within the boundaries of the retort site adjacent such a void, the unfragmented formation having a free face adjacent such void;
• placing an array of rock bolts in at least a portion of the unfragmented formation adjacent such a free face;
• placing a plurality of columnar explosive charges in the zone of unfragmented formation perpendicular to the free face, the distance from the ends of the column charges to the roof being at least twice the depth of penetration of the rock bolts into formation adjacent the roof;
• and
• detonating such explosive for explosively expanding the zone of unfragmented formation toward the free face, including the portion containing the array of rock bolts, for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.