Abstract: An in situ oil shale retort is formed by excavating a lower level void adjacent the bottom boundary of a retort site in a subterranean formation, leaving a zone of unfragmented formation within side boundaries of the retort overlying the void. At least a portion of the overlying zone is explosively expanded downwardly towards the void in a plurality of lifts. Vertical columnar explosive charges are placed in each lift and detonated in a single round with a time delay between successive lifts sufficient for formation of the first lift to move out of the way and not interfere with initial explosive expansion of formation in the next successive lift. Preferably, the explosive charges in a second lift are detonated after detonation of explosive charges in a first lift with a time delay in the range of from about five to thirty milliseconds per foot of burden distance of the charges in the second lift.

Abstract: A method for forming an in situ oil shale retort in a retort site in a subterranean formation is provided. The in situ oil shale retort contains a fragmented permeable mass of oil shale particles formed within top, bottom, and side boundaries of the retort site. At least one void is excavated in the subterranean formation within the boundaries of the retort site, while a zone of unfragmented formation is left within the boundaries of the retort site adjacent such a void. An inlet is formed in a zone of the retort adjacent the intersection of a first side boundary of the retort site and the top boundary of the retort site and an outlet is formed in a zone of the retort adjacent the intersection of a second side boundary of the retort site and the bottom boundary of the retort site. The second side boundary is on the opposite side of the retort site from the first side boundary.

Abstract: A row of horizontally spaced-apart in situ oil shale retorts is formed in a subterranean formation containing oil shale. Each row of retorts is formed by excavating development drifts at different elevations through opposite side boundaries of a plurality of retorts in the row of retorts. Each retort is formed by explosively expanding formation toward one or more voids within the boundaries of the retort site to form a fragmented permeable mass of formation particles containing oil shale in each retort. Following formation of each retort, the retort development drifts on the advancing side of the retort are closed off by covering formation particles within the development drift with a layer of crushed oil shale particles having a particle size smaller than the average particle size of oil shale particles in the adjacent retort.

Abstract: A fragmented permeable mass of formation particles containing oil shale and having a substantially uniformly distributed void fraction is formed in an in situ oil shale retort in a subterranean formation containing oil shale. The fragmented mass is formed by explosive expansion towards a horizontal free face. At least one generally horizontally extending void is formed in the subterranean formation and zones of unfragmented formation are left above and below such a void. An array of horizontally spaced apart substantially vertical columnar explosive charges is formed in at least one of the zones of unfragmented formation. The array of explosive charges includes a plurality of central explosive charges which are spaced apart from side boundaries of the retort and a plurality of outer explosive charges surrounding the central charges.

Abstract: A module of in situ oil shale retorts are formed in a row of retort sites in a subterranean formation. Each retort has top, bottom, and side boundaries of unfragmented formation and contains a fragmented permeable mass of formation particles. Two cross drifts are excavated through the retort sites along the row. One of the drifts is at a lower elevation near the floor of voids to be formed in the retort sites and along one side boundary of the retort sites. The other drift ramps upwardly at an end of the row for extending through the retort sites at a higher elevation near the roof of the voids excavated in the retort sites and along the opposite side boundaries of the retort sites. A horizontally extending slice is excavated at the elevation of the higher drift extending substantially to the side boundaries of a retort site for commencing a void within the retort site. The balance of the void is formed by benching from the slice to the elevation of the lower drift.

Abstract: Liquid and gaseous products are recovered from an in situ oil shale retort formed in a retort site in a subterranean formation containing oil shale. A void is excavated in the subterranean formation within the boundaries of the retort site and a zone of unfragmented formation is left in the retort site adjacent the void. A retort inlet is at one upper edge of the retort site and a retort outlet is at the lower edge of the retort site opposite the retort inlet.Explosive charges are placed in the zone of unfragmented formation and detonated in an asymmetrical time delay sequence for forming a fragmented permeable mass of formation particles which substantially fills the retort to the top boundary in the region of the retort inlet.

Abstract: Method and apparatus for remotely positioning individual explosive charges at preselected locations in substantially horizontal voids created by mining hard material such as coal are disclosed. The method includes the steps of positioning at least one charge proximate the entry of a void. The charge is then armed as by connecting a detonator cord thereto and inserted into a void to a preselected depth from a remote location. An apparatus is provided for positioning the charges at preselected locations in the voids and includes insert means having a body member for releasably engaging the charges during the positioning operation. The insert means is driven until the body member and charge propelled thereby is moved to a preselected location within the void where the charge is deposited.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale and having a substantially vertically extending first cleavage plane set and a substantially vertically extending second cleavage plane set intersecting the first set. The dispersion of the individual cleavage planes in the first and second cleavage plane sets is determined. The in situ retort is formed by excavating a vertical slot-shaped void within the boundaries of the retort site, leaving a remaining portion of the unfragmented formation within the retort site which is to be explosively expanded toward the slot. The unfragmented formation adjacent the slot has a pair of longer vertical free faces substantially aligned with the cleavage plane set having the lower dispersion. A pair of shorter vertical side walls of the slot can extend substantially perpendicular to the cleavage plane set having the lower dispersion.

Abstract: A method for forming a fragmented permeable mass of oil shale particles in an in situ oil shale retort in a subterranean formation containing oil shale is provided. At least one void is excavated within the retort site in the subterranean formation while zones of unfragmented formation are left adjacent such a void. The zones of unfragmented formation are then explosively expanded toward the void for forming the fragmented permeable mass of formation particles in the retort. To provide a fragmented mass with a flat top surface and reasonably uniform void fraction distribution, at least one of the zones of unfragmented formation is explosively expanded toward the void in a plurality of contiguous regions. Each such contiguous region has a free face adjacent the void and is expanded by first explosively expanding a first portion of that region toward the void. The free face of the first portion expanded is near the center of its respective region.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale and having horizontal cleavage planes extending parallel to the bedding of the formation and approximately orthogonal vertical cleavage plane sets extending perpendicular to the horizontal cleavage planes. The in situ retort is formed by excavating an opening or void in a retort site in the formation and placing explosive in the formation adjacent the void such that the explosive can fracture formation along the vertical cleavage planes and expand remaining formation within the retort site toward the void, forming a fragmented permeable mass of formation particles containing oil shale within the retort site.

Abstract: An explosive charging apparatus for charging explosive pellets to a bore drilled in a rock. The apparatus includes a body having coaxial pellet guiding first and second bores, the second bore being provided with a pellet supplying port. A cylinder is provided and has a piston with its rod extending into the second bore to force the pellet therein when the rod is advanced under an air pressure supplied to the cylinder. The rod is formed with an axial air passage opened to the second bore and adapted to be connected with a pressurized air source when the rod is advanced so as to supply air pressure to the second bore to thereby drive the explosive pellet to the first bore. The first bore is supplied with a lower air pressure which functions to feed the pellet in the first bore to the bore in the rock. The cylinder is associated with a pilot operated valve which receives a returning pilot pressure when the piston is fully advanced and an advancing pilot pressure when the piston is fully retracted.

Abstract: A non-electric delay blasting method is provided which comprises the use of single trunk line of detonating cord having a series of detonating relays, all of the same delay period, connected at spaced intervals along its length. Branch lines of detonating cord are connected in groups to the trunk line in the intervals between the relays and each branch line has a delay detonator of the same delay period attached thereto. The delay period of the relays is shorter than that of the delay detonators. The detonators within the groups detonate in a random manner. The method eliminates the need to use large numbers of different delay period detonators in a multi-charge blast thus simplifying preparation of the charge and reducing inventories.

Abstract: An array of explosive charges is formed in a retort site in a subterranean formation containing oil shale. The explosive charges that are located around the perimeter of the retort site are smaller than the explosive charges located more remote from the perimeter. Formation within the retort site is explosively expanded toward a void formed in the site by detonating the explosive charges. This explosive expansion of formation results in a fragmented permeable mass of formation particles in the retort. Damage to objects near the retort site, which is caused by seismic shock from the detonations, is minimized by using smaller explosive charges around the perimeter than in the center of the retort site.

Abstract: An in situ leaching or solution mining process is conducted in a subterranean cavity in communication with a well bore. The subterranean cavity is gradually enlarged by inducing spallation of formation particles and/or collapse of the roof into the cavity by repeatedly cycling the hydraulic pressure in the subterranean cavity. The hydraulic pressure is preferably increased during a period of at least about two hours. The hydraulic pressure can be gradually decreased during a period of at least about two hours or can be suddenly decreased. Rapid pressure pulses can be applied to liquid in the subterranean cavity by detonation of shaped charges of explosive with the axis of force of the charge being directed along the axis of the well.

Abstract: There is provided a method for forming an in situ retort containing a fragmented permeable mass of formation particles in a retort site within a subterranean formation. A void is excavated into the formation and a zone of unfragmented formation is left adjacent the void. A plurality of explosive charges are formed in the zone of unfragmented formation. At least one central explosive charge is in a central portion of the zone of unfragmented formation, and a plurality of outer explosive charges are in the zone of unfragmented formation nearer the side walls of the void than the central explosive charge. The distance from each such outer explosive charge to an adjacent side wall of the void is about equal to the crater radius of the outer explosive charge. The central and outer explosive charges are detonated for explosively expanding the zone of unfragmented formation toward the void for forming a fragmented permeable mass of formation particles in the in situ retort.

Abstract: A retort site in a subterranean formation containing oil shale is prepared for in situ retorting by excavating a void space in the retort site and then explosively expanding at least a portion of the remainder of the formation within the retort site toward the void space. The resultant fragmented mass explosively expanded toward the void space will be permeabilized by the void volume of the void space. The void space is initially formed by excavating at least three substantially parallel drifts through the retort site. At least two of the drifts are along opposed outside edges of the retort site and at least one drift is intermediate the two outside drifts. Excavation of the void space is conducted from the two outside drifts. A vertically extending slot is first excavated from each such drift upwardly into the proposed void space at one end of the retort site. The slot may be fanned above the drift so that the slots from the two outside drifts meet near the top of the void space.

Abstract: A modified in-situ retort for the retorting of oil shale is constructed by mining an open space having a volume of twenty-five to thirty-five percent of the volume of the retort in the bottom of the retort and thereafter blasting the oil shale that is to remain in the retort as rubble in a manner to cause random free fall of the shale particles onto the rubblized bed. Blasting occurs sequentially from the bottom of the unfragmented shale immediately above the open space to the top of the retort. At each blast, there is an open space below the shale to be broken in the blast having a volume at least one-third the volume of that shale, and the timing of the blasts is such that movement of the broken shale is not interfered with by shale broken in the preceding blast. There is no withdrawal of oil shale that would cause downward movement of the rubble that is to be retorted in-situ. The resultant in-situ retort is characterized by a high and uniform permeability.

Abstract: A distinction of the method is that, at the moment of release of ore, the ore flow in the zone of an outlet opening is divided into at least two parts by a vertical plane, and the ore flow is caused to swing transversely with respect to the direction of ore flow by alternately changing the density of ore in the portions of the flow. Oversized lumps of ore delivered to a loading drift are transferred along a ramp by-passing haulage vehicles to ventilating and man roads which are arranged at the level of haulage crosscuts and connected thereto at points opposite to the loading drifts. An apparatus for carrying out the method includes a working surface of a platform having three rigidly interconnected portions, the end portions extending parallel and at different levels, and a central portion inclined in the direction of ore flow.

Abstract: This invention relates to a method of recovering shale oil from a subterranean formation containing oil shale. Unfragmented formation is explosively expanded in a single round of explosions for moving formation located at about the center of a zone of unfragmented formation a greater distance in a given time interval after the beginning of the round than formation located in the unfragmented formation outward from about the center of the unfragmented formation.The explosive expansion forms a fragmented mass of formation particles containing oil shale in the subterranean formation forming an in situ oil shale retort.Gas is introduced into the fragmented permeable mass in the in situ oil shale retort for establishing a retorting zone in the fragmented permeable mass wherein oil shale is retorted to produce gaseous and liquid products, and for advancing the retorting zone through the fragmented mass. Gaseous and liquid products are withdrawn from the bottom of the retort.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale, a horizontally extending void is excavated within the boundaries of the retort site leaving a zone of unfragmented formation above and/or below such a void. A crack is propagated in at least one of the zones of unfragmented formation along the side boundaries of the retort site and thereafter the zone of unfragmented formation is explosively expanded towards such a void for forming a fragmented permeable mass of formation particles in the retort. Such a fragmented permeable mass is retorted in situ to produce shale oil.

Abstract: A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort is provided. A horizontally extending void is excavated in unfragmented formation containing oil shale and a zone of unfragmented formation is left adjacent the void. An array of explosive charges is formed in the zone of unfragmented formation. The array of explosive charges comprises rows of central explosive charges surrounded by a band of outer explosive charges which are adjacent side boundaries of the retort being formed. The powder factor of each outer explosive charge is made about equal to the powder factor of each central explosive charge. The explosive charges are detonated for explosively expanding the zone of unfragmented formation toward the void for forming the fragmented permeable mass of formation particles having a reasonably uniformly distributed void fraction in the in situ oil shale retort.

Abstract: A method for forming an in situ oil shale retort in a subterranean formation containing oil shale is provided. The in situ oil shale retort has a top boundary, generally vertically extending side boundaries, and a bottom boundary of unfragmented formation. A first portion of formation is excavated for forming at least one void within the boundaries, leaving a remaining portion of formation within the boundaries adjacent the void or voids. A remaining portion of unfragmented formation within the retort boundaries is explosively expanded toward such a void for forming a fragmented permeable mass of formation particles containing oil shale in the retort. A void space remains between the upper surface of the fragmented mass and overlying unfragmented formation. A lower portion of the overlying formation is explosively expanded downwardly toward the void space for substantially filling the retort with formation particles.

Abstract: A method is provided for flattening a non-planar combustion zone which is advancing through a fragmented permeable mass of formation particles in an in situ oil shale retort. To effect flattening of the non-planar combustion zone, a fragmented permeable mass of formation particles having generally horizontally extending layers of various void fraction is provided in the in situ retort. At least one layer has a substantially higher effective average void fraction than adjacent layers above and below this layer. When the advancing non-planar combustion zone enters the high void fraction layer, it spreads laterally across the layer. The resulting combustion zone is approximately flat in a plane transverse to its direction of advance when it exits the high void fraction layer.

Abstract: An in situ oil shale retort is formed within a subterranean formation containing oil shale. The retort contains a fragmented permeable mass of formation particles containing oil shale. A production level drift extends below the fragmented mass, leaving a lower sill pillar of unfragmented formation between the production level drift and the fragmented mass. During retorting operations, liquid and gaseous products are recovered from a lower portion of the fragmented mass. A liquid outlet line extends from a lower portion of the fragmented mass through the lower sill pillar for conducting liquid products to a sump in the production level drift. Gaseous products are withdrawn from the fragmented mass through a plurality of gas outlet lines distributed across a horizontal cross-section of a lower portion of the fragmented mass. The gas outlet lines extend from the fragmented mass through the lower sill pillar and into the production level drift.

Abstract: A fragmented permeable mass of formation particles is formed in an in situ oil shale retort in a subterranean formation containing oil shale. Formation is excavated to form a horizontally extending void in the subterranean formation and a support pillar of unfragmented formation is left in the void for supporting overlying unfragmented formation. The support pillar is prepared for explosive expansion by forming an array of explosive charges along the centerline of the pillar between its opposed free faces. The amount of explosive on each side of the centerline is about equal. Explosive is then detonated in the support pillar for expanding the pillar about equally toward both opposed free faces. Thereafter, explosive is detonated in unfragmented formation above and/or below the void for explosively expanding the formation toward the void to form the fragmented permeable mass of formation particles.

Abstract: Coal is extracted in a longwall working with two subsidiary galleries disposed respectively at the ends of the longwall coal-face. The coal is obtained at the longwall face, is loaded and removed with the aid of a continuous conveyor acting as a longwall-heading conveyor which delivers into one of the subsidiary galleries. In order to extract the coal a plurality of long drill-holes, respectively spaced from the coal-face and from each other by a spacing which corresponds to the effective force of an explosive charge provided with a fuse-cord, are bored in the coal starting from one of the subsidiary galleries. Each of the drill-holes extends the full effective length of the coal face and is loaded with such an explosive charge, and then filled with water under pressure. The charges are exploded in succession, starting with the drill-hole adjacent the coal-face, whereupon the coal so acquired is loaded and removed by the continuous conveyor.

Abstract: A subterranean formation containing oil shale is prepared for in situ retorting by initially excavating a lower level drift adjacent a lower portion of an in situ oil shale retort site and excavating an air level void above the retort site. An undercut is excavated below a zone of unfragmented formation remaining within the retort site above the lower drift. The undercut tapers downwardly and inwardly to an opening in the lower drift for forming a draw point for withdrawing fragmented formation particles from the retort site. Formation within the remaining zone of unfragmented formation is explosively expanded downwardly in lifts for forming a fragmented permeable mass of formation particles containing oil shale within the retort site. A plurality of vertical blasting holes drilled in the remaining zone of unfragmented formation are loaded with explosive from the air level void prior to blasting each lift.

Abstract: A subterranean formation containing oil shale is prepared for in situ retorting by initially excavating a void in a lower portion of a retort site. A primary sub-round of explosive is placed in a portion of formation within the retort site above the void, and a secondary sub-round of explosive is also placed in unfragmented formation above the void. In one embodiment, the primary sub-round comprises explosive placed in separate pairs of longitudinally spaced apart upwardly converging blasting holes. Explosive in the primary sub-round is detonated for fracturing unfragmented formation along a boundary defined by the upwardly converging blasting holes to separate a portion of formation from adjacent unfragmented formation for forming at least one new face above the separated portion of formation.

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 in a subterranean formation contains a fragmented permeable mass of formation particles. Such a fragmented mass is formed by excavating a horizontally extending void within the boundaries of the retort, leaving a zone of unfragmented formation above and/or below such a void. A plurality of vertical blasting holes are drilled in such a zone and loaded with explosive charges for forming an array of explosive charges sufficiently close together to interact and fragment formation substantially to a plane at the ends of the charges remote from the void. The scaled depth of burial of such an array is in the range of from about 6 to 12 mm/cal.sup.1/3. The explosive charges are detonated in a single round for expanding such a zone towards the void for forming the fragmented mass of particles in the retort.

Abstract: An in situ oil shale retort is formed in a subterranean formation by excavating voids adjacent the top and bottom boundaries of the retort, leaving an intermediate zone of unfragmented formation between the voids. The lower level void is substantially larger than the upper level void. A lower portion of the intermediate zone is explosively expanded downwardly towards the lower level void for forming a first moiety of a fragmented mass of formation particles in the retort and leaving a void spaace over the top of the first moiety having about the same volume as the upper level void. Thereafter an upper portion of the intermediate zone is explosively expanded upwardly towards the upper level void and downwardly towards the void space for forming a second moiety of the fragmented mass in the retort. The fragmented mass has an average void fraction up to about 25% and no substantial part has a void fraction less than about 20%.

Abstract: An in situ oil shale retort is formed in a subterranean formation wherein the oil shale retort contains a fragmented permeable mass of formation particles containing oil shale. A limited void is formed in the subterranean formation and zones of unfragmented formation are left above and below the void and are loaded with explosive for explosively expanding unfragmented formation toward the void. The explosive is placed into the zones of unfragmented formation for forming a substantially horizontal array of main explosive charges and at least one substantially horizontal array of satellite explosive charges. Each of the satellite explosive charges has a scaled point charge depth of burial substantially equal to the scaled point charge depth of burial of each of the main explosive charges and the actual depth of burial of each of the satellite explosive charges is less than the actual depth of burial of each of the main explosive charges.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale. The retort contains a fragmented permeable mass of formation particles containing oil shale and has a production level drift in communication with a lower portion of the fragmented mass for withdrawing liquid and gaseous products of retorting during retorting of oil shale in the fragmented mass. The principal portion of the fragmented mass is spaced vertically above a lower production level portion having a generally T-shaped vertical cross section. The lower portion of the fragmented mass has a horizontal cross sectional area smaller than the horizontal cross sectional area of the upper principal portion of the fragmented mass above the production level.

Abstract: Shale oil is recovered from a subterranean formation containing oil shale by excavating formation to form at least one void, leaving zones of unfragmented formation above and below each void and leaving at least one support pillar of unfragmented formation in the void. Explosive is placed in at least one of the zones of unfragmented formation for explosively expanding the zone of unfragmented formation toward the void. The pillar is prepared for explosive expansion by drilling substantially horizontal blastholes in the pillar and by loading explosive charges into the blastholes. Thereafter, the explosive charges are detonated in a single round of explosions for explosively expanding the pillar toward the void.At least one of the zones of unfragmented formation is then expanded toward the void to form a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale. Formation is excavated from within a retort site for forming a plurality of vertically spaced apart voids extending horizontally across different levels of the retort site, leaving a separate zone of unfragmented formation between each pair of adjacent voids, and leaving one or more pillars within each void for providing temporary roof support for unfragmented formation above each void. A plurality of horizontally spaced apart vertical blast holes are drilled in each zone of unfragmented formation below the voids. A pillar within a first void is offset horizontally from at least a portion of a pillar in a second void excavated directly below the first void. This provides an access region in the first void above at least a portion of the pillar in the second void so that vertical blast holes can be drilled into a zone of unfragmented formation below the pillar in the second void from the access region in the first void.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale, a horizontally extending void is excavated within the boundaries of the retort site leaving a zone of unfragmented formation above and/or below such a void, at least one pillar of unfragmented formation is left within the side boundaries of such a void for providing temporary support for overburden above the void, such a pillar is explosively expanded so that a principal portion of the pillar fragments travel to the side boundaries of the void and such a zone of unfragmented formation is explosively expanded toward the void. Accumulation of sufficient pillar fragments adjacent the side boundaries of the retort can substantially offset a tendency for fragments of the expanded zone of formation to form a mound thereby forming a fragmented permeable mass of formation particles within the retort with a reasonably flat upper surface. Such a fragmented permeable mass is retorted in situ to produce shale oil.

Abstract: The present invention comprises a method of mining a solid substance, such as coal, minerals, or the like, from an underground deposit in one of a plurality of earth strata. Void areas are created in the deposit so as to generally define an area within the deposit which is to be enclosed. Plugging material is injected into the void areas to form a relatively impervious barrier enclosing the aforementioned area of the deposit and isolating it from the remainder of the earth strata in which it is located. Conversion media, such as solvents or oxidation supporting media, are then injected into the enclosed area to convert the substance therein into flowable form. Finally, the substance as so converted is withdrawn from the enclosed area.

Abstract: There is provided a method for forming an in situ oil shale retort in a subterranean formation containing oil shale. At least one void is excavated in the formation, leaving zones of unfragmented formation adjacent the void. An array of main blastholes is formed in the zone of unfragmented formation and at least one explosive charge which is shaped for forming a high velocity gas jet is placed into a main blasthole with the axis of the gas jet extending transverse to the blasthole. The shaped charge is detonated for forming an auxiliary blasthole in the unfragmented formation adjacent a side wall of the main blasthole. The auxiliary blasthole extends laterally away from the main blasthole. Explosive is placed into the main blasthole and into the auxiliary blasthole and is detonated for explosively expanding formation towards the free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.

Abstract: A subterranean formation containing oil shale is prepared for in situ retorting by forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort site. Formation is initially excavated from the retort site for forming one or more voids extending horizontally across the retort site, leaving a zone of unfragmented formation adjacent such a void. In one ambodiment, an array of rocks bolts are anchored in at least a portion of the roof adjacent such a void for providing reinforcement of unfragmented formation above the void. Vertical blasting holes are drilled in the zone of unfragmented formation adjacent the void. Explosive is placed in the blasting holes and detonated for explosively expanding the zone of unfragmented formation toward the void, including the rock bolted portion of the roof, for forming at least a portion of a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort.

Abstract: An in situ oil shale retort is formed in a subterranean formation containing oil shale. A void can be formed in formation within the retort site by directing fluid under pressure against a zone of relatively weakened formation, such as tuffs, gravel beds, or fractured oil shale, to erode such weakened formation into particle form, leaving a void space adjacent a remaining zone of unfragmented formation within the retort site. The void space can be formed by drilling a bore hole into the zone of weakened formation, placing a jet nozzle in the bore hole, and forcing a fluid such as water through the nozzle against the weakened formation for eroding it to form the void space. Eroded formation particles are passed to the bottom of the bore hole. Such water jetting techniques can be used to form voids in zones of weakened formation interspersed throughout the retort site.

Abstract: An array of in situ oil shale retorts is formed in a development region in a subterranean formation containing oil shale. At least one void is excavated in each retort site, and remaining formation within each retort site is explosively expanded toward the void for forming a fragmented permeable mass of formation particles containing oil shale in each in situ retort. Overburden loads over an area of the development region are carried largely by the fragmented masses and partly by unfragmented partitions between retorts. Subsidence of overburden following explosive expansion is controlled at the boundary of the development region to avoid an abrupt change in the overburden load supported largely by the fragmented masses inside the boundary and the overburden load supported by unfragmented formation outside the boundary.

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 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: Oil shale formation is explosively expanded toward a limited void volume for forming an in situ oil shale retort in a subterranean formation containing oil shale. In one embodiment, the retort is formed by excavating a narrow vertical slot diagonally across a retort site of rectangular horizontal cross-section, leaving separate triangular zones of unfragmented formation within the retort site on opposite sides of the diagonal slot. Explosive is placed in a plurality of vertical blasting holes drilled in each triangular zone of formation, and such explosive is detonated for explosively expanding formation within the triangular zones toward vertical free faces adjacent the slot for forming a fragmented permeable mass of formation particles containing oil shale.

Abstract: The locus of a processing zone advancing through a fragmented permeable mass of formation particles in an in situ oil shale retort in a subterranean formation containing oil shale and which generates an effluent fluid is determined by placing a radionuclide source for providing an identifiable radionuclide, and monitoring effluent fluid from the processing zone for presence of such radionuclide. The radionuclide source provides radionuclide at a predetermined temperature.

Abstract: A method is provided for recovering shale oil from a subterranean formation containing oil shale. Unfragmented formation is prepared for explosive expansion to form an oil shale retort by excavating at least one limited void in the subterranean formation and forming an array of spaced apart blastholes in the formation. A substantially horizontal array of explosive charges is formed by placing explosive into each blasthole wherein the scaled point charge depth of burial of the explosive charge in each blasthole is substantially equal to the equivalent scaled point charge depth of burial of the array of the explosive charges. Explosive charges are detonated in a single round for explosively expanding the unfragmented formation to form the in situ oil shale retort.Retorting is commenced and liquid and gaseous products of retorting are withdrawn from the retort.

Abstract: A method of reclaiming a highwall or sharp cliff like exposure mining site. The method includes the steps of placing a first series of directional charges at preselected locations in each of the auger, longwall or deep mine entry holes proximate the opening of the hole on the face of the highwall. Directional charges are positioned on the floor of the holes and pointed upward, obviating the need to drill charge placement holes. Such solid placement maximizes the explosive impact on the overburden above the charges thereby creating rubble from the overburden and tearing out sections of the in-situ material separating the holes. In one embodiment, a further series of charges is detonated at a preselected interval in time and depth from the detonation of the first series of directional charges to provide a synergistic explosive effect to accomplish the reclamation process.

Abstract: An in situ oil shale retort is formed with an upper surface of a fragmented permeable mass in the retort separated from a top boundary of unfragmented formation, creating an inlet plenum void. A primary combustion zone is established in the fragmented mass, and such primary combustion zone is caused to spread laterally by the establishment of a secondary combustion zone. During a first period of time, the temperature in the inlet plenum void is maintained at less than the temperature at which unfragmented formation from above the top boundary will slough into the void. The primary combustion zone is advanced through the retort and liquid and gaseous products of retorting are withdrawn. During a second period of time the temperature in the inlet plenum void is increased to increase the temperature of the top boundary of unfragmented formation to a temperature which will cause unfragmented formation from above the top boundary to slough into the void.

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: An in situ oil shale retort is formed in a subterranean formation containing oil shale. Such an in situ oil shale retort contains a fragmented permeable mass of formation particles containing oil shale including a lower moiety and an upper moiety of said fragmented mass. The fragmented permeable mass of formation particles has top, bottom and side boundaries. A first portion of the formation is excavated from within the boundaries of the fragmented mass being formed to form a void. A second portion of the formation is excavated from within the boundaries of the fragmented mass being formed to form at least one additional void in communication with the first void and leaving a third portion to be expanded toward such an additional void. Fragmented particles from the excavation of such an additional void are deposited in the first void to provide a lower moiety of the fragmented permeable mass of formation particles.