Method for explosively expanding a pillar for forming 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, the in situ oil shale retort containing a fragmented permeable mass of formation particles within the boundaries of the retort comprising the steps of:

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort site leaving zones of unfragmented formation above and below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• placing explosive in such a pillar, the amount of explosive being sufficient to eject a principal portion of fragments of the pillar to at least the side boundaries of the void;
• placing explosive in at least one such zone of unfragmented formation;
• detonating a first portion of explosive in the pillar for preferentially explosively expanding a portion of the pillar and ejecting pillar fragments towards at least one adjacent side boundary of the void and thereafter detonating another portion of explosive in the pillar for explosively expanding the balance of the pillar towards side boundaries of the void;
• and
• detonating explosive in such a zone of unfragmented formation for explosively expanding the zone towards the void, the time interval between detonation of explosive in the pillar and detonation of explosive in the zone being at least sufficient for a principal portion of the pillar fragments to travel to the side boundaries of the void.

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

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort leaving zones of unfragmented formation above and below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• explosively expanding such a pillar so that a principal portion of the fragments of the pillar travel to side boundaries of the void;
• and
• explosively expanding at least one such zone of unfragmented formation towards the void for forming a fragmented permeable mass of particles in the retort.

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

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort leaving zones of unfragmented formation above and below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• explosively expanding a first portion of such a pillar preferentially towards at least one adjacent side boundary of the void and thereafter explosively expanding the balance of the pillar so that a principal portion of the fragments of the pillar travel to portions of the retort site adjacent to side boundaries of the void;
• and
• explosively expanding at least one such zone of unfragmented formation towards the void for forming a fragmented permeable mass of particles in the retort.

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

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort site, leaving a zone of unfragmented formation above and/or below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• explosively expanding such a pillar for forming a generally concave permeable mass of pillar fragments;
• and
• explosively expanding such a zone of unfragmented formation towards such a void for forming a fragmented permeable mass of particles in the retort.

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

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort site, leaving zones of unfragmented formation above and below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• placing explosive in such a pillar;
• placing explosive in at least one such zone of unfragmented formation;
• detonating explosive in the pillar for explosively expanding the pillar and ejecting pillar fragments toward side boundaries of the void;
• and
• at least about one-half second after detonating explosive in the pillar, detonating explosive in such a zone of unfragmented formation for explosively expanding the zone towards the void.

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

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort site, leaving zones of unfragmented formation above and below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• placing explosive in such a pillar;
• placing explosive in at least one such zone of unfragmented formation;
• detonating a first portion of explosive in the pillar for preferentially explosively expanding a portion of the pillar towards at least one side boundary of the void and thereafter detonating another portion of explosive in the pillar for explosively expanding the balance of the pillar and ejecting pillar fragments toward side boundaries of the void;
• and
• at least about one-half second after detonating explosive in the pillar, detonating explosive in such a zone of unfragmented formation for explosively expanding the zone towards the void.

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

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort site, leaving zones of unfragmented formation above and below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• explosively expanding such a pillar for forming a fragmented permeable mass of particles from the pillar;
• and
• explosively expanding such a zone of unfragmented formation towards such a void for forming a fragmented permeable mass of particles in the retort wherein such pillar is explosively expanded a sufficient time before explosive expansion of such zone of unfragmented formation that the fragmented mass of particles from the pillar is thicker near at least one side boundary of the retort than it is near the center of the retort.

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

• excavating a subterranean drift through a side boundary of the retort site;
• excavating at least one horizontally extending void in communication with the drift within the side boundaries of the retort site, leaving a zone of unfragmented formation above and/or below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• explosively expanding such a pillar for filling a principal portion of the cross section of the drift near the side boundary of the retort site with pillar fragments;
• and
• explosively expanding such a zone of unfragmented formation towards the void for forming a fragmented permeable mass of formation particles in the retort.

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

• excavating a subterranean drift through a side boundary of the retort site;
• excavating at least one horizontally extending void in communication with the drift within the side boundaries of the retort site, leaving a zone of unfragmented formation above and/or below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• explosively expanding a first portion of such a pillar preferentially towards at least one side boundary of the void and thereafter explosively expanding the balance of the pillar for filling a principal portion of the cross section of the drift near the side boundary of the retort site with pillar fragments;
• and
• explosively expanding such a zone of unfragmented formation towards the void for forming a fragmented permeable mass of formation particles in the retort.

In a method for forming an in situ oil shale retort in a subterranean formation containing oil shale, the in situ oil shale retort containing a fragmented permeable mass of formation particles within the boundaries of the retort, comprising the steps of:

• excavating at least one horizontally extending void within the boundaries of an in situ oil shale retort site leaving a zone of unfragmented formation above and/or below such a void and leaving at least one pillar of unfragmented formation within the side boundaries of such a void for providing temporary support for overlying formation above the void;
• explosively expanding such a pillar;
• and explosively expanding such a zone of unfragmented formation towards the void for forming a fragmented permeable mass of particles in the retort, the improvement comprising:
• providing a sufficient time between explosive expansion of such pillar and explosive expansion of such a zone of unfragmented formation for accumulating sufficient pillar fragments adjacent side boundaries of the retort for substantially offsetting a tendency of fragments of the explosively expanded zone to form a mound, thereby forming a fragmented permeable mass of particles in the retort with a reasonably flat upper surface.