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: 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 Gaseous and liquid products are withdrawn from the bottom of the retort.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: A temporary gas seal is provided in a gas level drift of an in situ oil shale retort system which includes a production region having a panel of retorts producing gaseous and liquid products and an adjacent retort preparation region where a panel of in situ retorts is being prepared for production. A portion of the gas level drift is connected to the active retorts for withdrawing off gas while adjacent portions of the gas level drift are being developed. Portions of the gas level connected to the active retorts are temporarily sealed by a gas isolation barrier to isolate workers from toxic off gas. The gas isolation barrier can be a bulkhead with one or more openings each sealed by a remotely removable seal, such as a flexible membrane, or a plate that can be remotely removed or opened to unseal such a bulkhead opening.

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: 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: A downhole delay assembly is provided which can be placed into a blasthole for initiation of explosive in the blasthole. The downhole delay assembly includes at least two detonating time delay devices in series in order to effect a time delay of longer than about 200 milliseconds in a round of explosions. The downhole delay assembly provides a protective housing to prevent detonation of explosive in the blasthole in response to the detonation of the first detonating time delay device. There is further provided a connection between the first and second time delay devices. The connection is responsive to the detonation of the first detonating time delay device and initiates the second detonating time delay device.A plurality of such downhole delay assemblies are placed downhole in unfragmented formation and are initiated simultaneously for providing a round of explosive expansions.

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: There is provided a method of forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale. The in situ oil shale retort contains a fragmented permeable mass of formation particles. A first portion of formation is excavated from within the boundaries of the retort being formed to form at least one void. The surface of the formation defining such a void provides at least one free face extending through the formation. The second portion of formation is left within the boundaries of the retort being formed to be explosively expanded toward the void.At least two arrays of explosive charges are formed in the second portion of formation wherein the first array of explosive charges has a first burden distance and the second array of explosive charges has a second burden distance wherein the second burden distance is less than the first burden distance.

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: 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: 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: 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 forming an in situ oil shale retort with an open space or inlet plenum void between the top boundary of the fragmented permeable mass of oil shale particles and the unfragmented formation above the retort. The method comprises excavating at least one horizontal void in the formation, placing explosive into the unfragmented formation above and below the void, and then explosively expanding formation above the void prior to explosively expanding formation below the void. The additional time for expansion of formation above the void, as compared with that below the void, permits non-uniform expansion and leaves an open space over the top of the fragmented mass.