Abstract: Following the conventional mining of rich oil shale for conventional above ground retorting, by horizontally extensive room and pillar mining operations, additional shale oil and related product may be secondarily recovered from the oil shale formation by in-situ retort formation and combustion. The secondary recovery steps would involve initially the identification of a large horizontally extending area, normally located between barrier pillars, which may be blocked off for the in-situ retort. Suitable shale oil drain arrangements may then be provided along one lower edge of this in-situ retorting area. Along the opposite lower edge of the in-situ retorting area, conduits may be provided for withdrawing product gas from the retort area. The retort area may then be sealed, and rubblized by blasting the pillars and caving in the roof to provide the appropriate 15% to 30% void volume for in-situ retorting.

Abstract: A ventilation and process air distribution system is provided for an in situ oil shale retort system which includes a production region having a cluster of retorts producing gaseous and liquid products and a retort preparation region where in situ retorts are being prepared for production. An underground air delivery drift system distributes process air to the production region and ventilation air to underground workings in the retort preparation region. A liquid collection drift system extends at or below the bottoms of the retorts in the production region and in the retort preparation region. The liquid collection drifts connect to an exhaust airway leading above ground and having an induction fan for inducing ventilation air to flow through the retort preparation region at a pressure lower than ambient air pressure above ground.

Abstract: A subterranean formation containing oil shale is prepared for in situ retorting by initially excavating a plurality of vertically spaced apart voids within a retort site, leaving an intervening zone of unfragmented formation between an adjacent pair of such voids. The intervening zone has substantially parallel upper and lower horizontal free faces adjoining the voids. At least one pancake-shaped load of explosive is placed in the intervening zone. The pancake-shaped explosive load has faces which are substantially parallel to the upper and lower free faces, and the length of the axis of the explosive load is less than the radius of the load. The explosive load is detonated for explosively expanding formation toward the upper and lower free faces for forming an in situ retort containing a fragmented permeable mass of formation particles.

Abstract: An in situ oil shale retort is formed in a subterranean oil shale deposit by excavating a columnar void having a vertically extending free face, drilling blasting holes adjacent to the columnar void, loading the blasting holes with explosive, and detonating the explosive in a single round to expand the shale adjacent to the columnar void toward the free face to fill with fragmented oil shale the columnar void and the space in the in situ retort originally occupied by the expanded shale prior to the expansion. A room having a horizontal floor plan that coincides approximately with the horizontal cross section of the retort to be formed is excavated so as to intersect the columnar void. The room can lie above the columnar void, below the columnar void, or intermediate the ends of the columnar void. The expanded or fragmented shale has a low average void volume. The void volume of the fragmented shale increases at the bottom of the in situ retort.

Abstract: A fragmented recovery zone in a subterranean ore seam has a polygonal cross section with a low void volume and a conical funnel-shaped bottom with a high void volume. Recovered constituents are removed from the recovery zone at the point of convergence of the funnel.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale and including underground workings by excavating a means for access to a retort site in the formation, excavating a void in the retort site at least in part from the means for access, leaving a remaining portion of the unfragmented formation in the retort site adjacent the void, placing explosive in the remaining portion of formation, and detonating the explosive in such unfragmented formation in a single round to explosively expand formation toward the void for forming a fragmented permeable mass of formation particles containing oil shale in an in situ retort. A permeable barrier is provided between the void and the underground workings which provide means for access to such a void.

Abstract: A subterranean formation containing oil shale is prepared for in situ retorting by initially excavating at least one void adjacent a zone of unfragmented formation to be expanded. The zone of unfragmented formation has a substantially horizontal free face adjoining the void. At least one support pillar of unfragmented formation is left in the void for supporting overlying formation. Explosive is placed in the zone of unfragmented formation, and in such a support pillar. Explosive in such a pillar and in the zone of unfragmented formation is detonated in a single round of explosions with a time delay between detonation of explosive in such a pillar and detonation of explosive in the zone of unfragmented formation for first expanding such a pillar toward the void and then expanding unfragmented formation toward the void. The time delay is sufficient for creation of free face at the juncture of such a pillar and the zone of unfragmented formation.

Abstract: The locus of a processing zone advancing through a fragmented permeable mass of particles in an in situ oil shale retort in a subterranean formation containing oil shale is determined by withdrawing a sample of gas passing through the retort through a channel through unfragmented formation and in fluid communication with the retort, and analyzing the composition of withdrawn gas. The channel can be artificially formed such as by hydraulic fracturing of unfragmented formation, or can be a naturally occurring permeable layer such as a tuff bed in the formation containing oil shale.

Abstract: A tunnel is formed above an in situ oil shale retort in a subterranean deposit containing oil shale. A void is excavated in the retort site and remaining deposit in the retort site is fragmented by explosively expanding toward the void to form a subterranean cavity containing a fragmented permeable mass of particles containing oil shale. The top of the fragmented mass is spaced downwardly from the tunnel to leave therebetween a pillar of unfragmented deposit. A retorting gas is introduced into the retort through a plurality of sloping passages from the tunnel for retorting oil shale in the fragmented mass. The liquid and gaseous products of such retorting are removed from the bottom of the retort. A portion of the carbonaceous products are used for generating electricity. In working a large area of deposit, a plurality of retorts are arranged in rows and columns.

Abstract: A subterranean formation containing oil shale is prepared for in situ retorting by initially excavating a pair of spaced apart voids, leaving an intervening zone of unfragmented formation between the voids. The intervening zone has substantially parallel free faces adjoining the void. A plurality of elongated blasting holes are formed in the intervening zone of unfragmented formation, the longitudinal axis of each blasting hole being substantially perpendicular to the parallel free faces of the intervening zone. At least two deck loads of explosives are placed in each blasting hole, with each load being longitudinally spaced apart from each adjacent load by stemming. The loads of explosive are then detonated in a single round of explosions with a time delay between adjacent loads for expanding formation in the intervening zones toward both voids. The fragmented mass of formation particles is then retorted to recover shale oil from the oil shale.

Abstract: A row of horizontally spaced apart in situ oil shale retorts is formed in a subterranean formation containing oil shale. Each row is formed by excavating at least a pair of upper and lower retort access drifts at elevations within the top and bottom boundaries of the retort sites. The access drifts extend through opposite side boundaries of a plurality of retorts in such row. Each retort is formed by excavating upper and lower horizontal voids at the levels of the upper and lower retort access drifts, respectively, such voids being excavated laterally from the access drift within the side boundaries of the retort sites. Each retort is formed by explosively expanding formation toward the upper and lower voids within the boundaries of the retort site to form a fragmented permeable mass of particles containing oil shale in each retort.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale. The retort contains a fragmented permeable mass of particles containing oil shale. An open base of operation is excavated in the formation at an elevation above the fragmented mass to be formed, and an access drift is excavated to provide access to the bottom of the retort site. Formation is explosively expanded to form the fragmented mass between the access drift and an elevation spaced below the bottom of the base of operation, leaving a horizontal sill pillar of unfragmented formation between the top of the fragmented mass and the bottom of the base of operation. The sill pillar provides a safe base of operation above the fragmented mass after it is formed. The fragmented mass is formed by, among other steps, drilling blasting holes from the base of operation down through the sill pillar and then detonating explosive in such holes to form the fragmented mass of particles in the retort below the sill pillar.

Abstract: A row of horizontally spaced apart in situ oil shale retorts is formed in a subterranean formation containing oil shale. Each row is formed by excavating at least a pair of upper and lower retort access drifts at elevations within the top and bottom boundaries of the retort sites. The access drifts extend through opposite side boundaries of a plurality of retorts in such row. Each retort is formed by excavating upper and lower horizontal voids at the levels of the upper and lower right access drifts, respectively, such voids being excavated laterally from the access drift within the side boundaries of the retort sites. Each retort is formed by explosively expanding formation toward the upper and lower voids within the boundaries of the retort site to form a fragmented permeable mass of particles containing oil shale in each retort.

Abstract: In raise bore drilling, a drill string of non-round cross-sectional configuration is connected through a pilot hole from a raise bore bit at the lower end of the pilot hole to a raise bore drilling rig at the upper end of the hole. The drill string is defined by a number of serially connected individual pipe lengths. The drill string configuration preferably is hexagonal except at one end of each length where the pipe length is round for a distance which corresponds to the length of a female threaded connection component defined by that end of the pipe length. The other end of each pipe length defines a cooperating male threaded connection component.

Abstract: A subterranean deposit containing oil shale is prepared for in situ retorting by initially excavating a plurality of vertically spaced apart voids of similar horizontal cross section located one above another within the deposit. A zone of unfragmented deposit temporarily left between each adjacent pair of voids has a thickness greater than the smallest lateral dimension of the voids above and below it. Explosive placed in a lower portion of the unfragmented zone is detonated to expand the lower portion of the unfragmented zone into the lower void, leaving the upper portion of the zone intact and creating a space free of fragmented particles below it. Thereafter, the remaining portion of the unfragmented zone is explosively expanded into the open space below it and into the upper void, forming a subterranean room filled with a fragmented mass of particles having a void volume substantially equal to the total initial volume of the voids.

Abstract: A subterranean deposit containing oil shale is prepared for in situ retorting by initially excavating a plurality of vertically spaced apart voids of similar horizontal cross section located one above another within the deposit. A plurality of vertically spaced apart zones of unfragmented deposit are temporarily left between the voids, each unfragmented zone having a thickness of less than about 190 percent of the smallest lateral dimension of the voids above and below it. Explosive placed in each of the unfragmented zones is detonated, preferably in a single round to expand each unfragmented zone into the voids on either side of it and form a subterranean room containing a fragmented mass of particles having a void volume equal to the void violume of the initial voids. Retorting of the expanded mass is then carried out to recover shale oil from the oil shale.

Abstract: An in situ oil shale retort is formed in a subterranean oil shale deposit by excavating a columnar void having a vertically extending free face, drilling blasting holes adjacent to the columnar void and parallel to the free face, loading the blasting holes with explosive, and detonating the explosive in a single round to expand the shale adjacent to the columnar void toward the free face in layers severed in a sequence progressing away from the free face and to fill with fragmented oil shale the columnar void and the space in the in situ retort originally occupied by the expanded shale prior to the expansion. A room having a horizontal floor plan that coincides approximately, with the horizontal cross section of the retort to be formed is excavated so as to intersect the columnar void. The blasting holes are drilled and loaded with explosive from the room. The room can lie above the columnar void, below the columnar void, or intermediate the ends of the columnar void.

Abstract: A technique is provided for loading an ammonium nitrate-fuel oil (ANFO) explosive mixture upwardly into a vertical blast hole extending as much as 70 feet or more from the open end at the face of the rock structure into which the blast hole is drilled. In order to achieve adequate packing in the hole the ANFO is maintained "soft" by keeping the ammonium nitrate particles substantially free of anti-caking materials. First the hole surface is moistened with water. If the surface dries before the hole is completely loaded, the remaining unloaded length is again moistened. The particles of explosive are blown into the hole through a hose as a mixture with air at a velocity sufficient to bring about packing and sticking of the ANFO in the blast hole. The packing is sufficient to keep the ANFO from falling out of an upwardly extending blast hole.

Abstract: A technique is described for reducing the content of oil and water in the flue gas recovered from the bottom of an underground in situ oil shale retort. In such a retort air is passed downwardly to sustain a combustion zone for retorting oil which is recovered at the bottom. Flue gas recovered from the bottom of the retort contains water vapor and oil and water aerosols. These are removed from the flue gas by passing it a substantial distance upwardly through cool overburden so that the flue gas is cooled below its dew point so that water condenses in the vertical conduit and aerosols are dropped out on the walls. The oil and water are recovered at the bottom of the conduit and stored in an underground sump.

Abstract: A technique is provided for cooling the flue gas or off gas from the bottom of an in situ oil shale retort. The gas is collected in a conduit that has a vertical portion through which the gas flows upwardly. It is then withdrawn from the retort through a gas tight bulkhead. Water is sparged downwardly through the vertical portion of the conduit for cooling and cleaning the gas. Means are provided for draining the sparged water into a sump at the bottom of the retort wherein oil and water are collected. Water and oil are separated and the water may be recycled for additional cooling.