Fracturing of pillars for enhancing recovery of oil from in situ oil shale retort

A method for recovery of shale oil from a fragmented permeable mass of particles containing oil shale in an in situ oil shale retort in a subterranean formation containing oil shale and from fractured unfragmented formation containing oil shale adjacent the fragmented permeable mass of particles, said retort having pillars of a first portion of unfragmented formation defining boundaries for the fragmented permeable mass of particles, said fragmented permeable mass being obtained by fragmenting part of a second portion of the formation within such boundaries;

• comprising the steps of:
• forming at least one access hole in unfragmented formation in the vicinity of such a boundary;
• propagating fractures from the access hole into at least a portion of unfragmented formation in the first portion and adjacent the second portion;
• excavating a part of the second portion of the formation to form at least one void and leaving a remaining unfragmented part of said second portion extending away from such an excavated void, the excavated void volume being in the range of from about 10 to 25 percent of the volume of the fragmented permeable mass being formed;
• explosively expanding said remaining part of said second portion toward such an excavated void for forming the fragmented permeable mass of particles;
• passing a retorting gas through the fragmented mass of particles containing oil shale;
• and
• recovering carbonaceous products including shale oil from the retort.

A method for forming an in situ oil shale retort containing a fragmented permeable mass of particles in a subterranean formation containing oil shale, said retort having pillars of a first portion of unfragmented formation defining boundaries for a fragmented permeable mass of particles, said fragmented permeable mass being obtained by fragmenting part of a second portion of the formation within such boundaries, comprising the steps of:

• fracturing unfragmented formation containing oil shale in the first portion and adjacent the second portion;
• excavating a part of the second portion of the formation to form at least one void and leaving a remaining unfragmented part of said second portion extending away from such an excavated void;
• and
• explosively expanding said remaining part of said second portion toward such an excavated void for forming the fragmented permeable mass of particles, having a void volume substantially the same as the volume of the excavated part of the second portion.

A method for recovery of shale oil from a fragmented permeable mass of particles in an in situ oil shale retort in a subterranean formation containing oil shale and from fractured unfragmented formation containing oil shale adjacent the fragmented permeable mass, said retort having pillars of a first portion of unfragmented formation defining boundaries for the fragmented permeable mass of particles, said fragmented permeable mass being obtained by fragmenting part of a second portion of the formation within such boundaries, comprising the steps of:

• fracturing unfragmented formation containing oil shale in the first portion and adjacent the second portion;
• excavating a part of the second portion of the formation to form at least one void and leaving a remaining unfragmented part of said second portion extending away from such an excavated void;
• explosively expanding said remaining part of said second portion toward such an excavated void for forming the fragmented permeable mass of particles, having a void volume substantially the same as the volume of the excavated part of the second portion, and
• retorting the fragmented permeable mass of particles containing oil shale and fractured formation containing oil shale adjacent to the fragmented permeable mass for recovering carbonaceous products including shale oil therefrom.