Method of uniform rubblization for limited void volume blasting

Claim 1

A method for recovering liquid and gaseous products from an in situ oil shale retort in a subterranean formation containing oil shale comprising the steps of: excavating a first portion of the formation from within the boundaries of the retort being formed to form at least one void, the surface of the formation defining such a void providing at least one free face within the boundaries of the retort being formed, and leaving a second portion of the formation within the boundaries of such retort being formed and extending away from such a free face, such a second portion to be explosively expanded toward such a void; placing at least two arrays of explosive charges in such a second portion of formation, the first array of explosive charges having a first burden distance measured from such a free face and the second array of explosive charges having a second burden distance measured from the first array of explosive charges, the second burden distance being less than the first burden distance, wherein the equivalent scaled point charge depth of burial of the first array of explosive charges is substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges, the first array of explosive charges being closer to the free face than the second array of explosive charges; detonating such explosive charges for explosively expanding such a second portion of formation toward such a void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort; introducing gas into the fragmented permeable mass in the in situ oil shale retort for establishing a retorting zone in the fragmented mass wherein oil shale is retorted to produce gaseous and liquid products and for advancing the retorting zone through the fragmented mass; and withdrawing gaseous and liquid products from the retort.

Claim 2

A method for recovering liquid and gaseous products from an in situ oil shale retort in a subterranean formation containing oil shale comprising the steps of: excavating a first portion of the formation from within the boundaries of the retort being formed to form at least one void, the surface of the formation defining such a void providing at least one free face within the boundaries of the retort being formed, and leaving a second portion of the formation within the boundaries of such retort being formed and extending away from such a free face, such a second portion to be explosively expanded toward such a void; placing at least two arrays of explosive charges in such a second portion of formation, the first array of explosive charges having a first burden distance measured from such a free face and the second array of explosive charges having a second burden distance measured from the first array of explosive charges, the second burden distance being less than the first burden distance, wherein the equivalent scaled point charge depth of burial of the first array of explosive charges is substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges, the first array of explosive charges being closer to the free face than the second array of explosive charges; detonating such explosive charges for explosively expanding such a second portion of formation toward such a void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort; introducing gas into the fragmented permeable mass in the in situ oil shale retort for establishing a retorting zone in the fragmented mass wherein oil shale is retorted to produce gaseous and liquid products and for advancing the retorting zone through the fragmented mass; and withdrawing gaseous and liquid products from the retort.

Claim 15

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one void, a surface of the formation defining such a void providing at least a first free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such first free face, such second portion to be explosively expanded toward such a void; placing at least a first and a second array of spaced apart explosive charges in such a second portion of formation, the first array being closer to the first free face than the second array wherein the burden distance of the first array measured from the first free face is greater than the burden distance of the second array measured from the first array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort.

Claim 16

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one void, a surface of the formation defining such a void providing at least a first free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such first free face, such second portion to be explosively expanded toward such a void; placing at least a first and a second array of spaced apart explosive charges in such a second portion of formation, the first array being closer to the first free face than the second array wherein the burden distance of the first array measured from the first free face is greater than the burden distance of the second array measured from the first array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort.

Claim 24

A method for forming an in situ oil shale retort in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented mass of formation particles containing oil shale, comprising the steps of: excavating a first portion of the formation from within the boundaries of the retort being formed to form at least one void, the surface of the formation defining such a void providing at least one free face within the boundaries of the retort being formed, and leaving a second portion of the formation within the boundaries of such retort being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; placing at least two arrays of explosive charges in such a second portion of formation, the first array of explosive charges having a first burden distance measured from such a free face and the second array of explosive charges having a second burden distance measured from the first array of explosive charges, the second burden distance being less than the first burden distance, wherein the equivalent scaled point charge depth of burial of the first array of explosive charges is substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges, the first array of explosive charges being closer to the free face than the second array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward such a void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort.

Claim 25

A method for forming an in situ oil shale retort in a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented mass of formation particles containing oil shale, comprising the steps of: excavating a first portion of the formation from within the boundaries of the retort being formed to form at least one void, the surface of the formation defining such a void providing at least one free face within the boundaries of the retort being formed, and leaving a second portion of the formation within the boundaries of such retort being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; placing at least two arrays of explosive charges in such a second portion of formation, the first array of explosive charges having a first burden distance measured from such a free face and the second array of explosive charges having a second burden distance measured from the first array of explosive charges, the second burden distance being less than the first burden distance, wherein the equivalent scaled point charge depth of burial of the first array of explosive charges is substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges, the first array of explosive charges being closer to the free face than the second array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward such a void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort.

Claim 36

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one limited void, a surface of the formation defining such a void providing at least one free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; forming an array of spaced apart blastholes in such a second portion of formation, the array comprising at least two rows of blastholes, wherein the burden distance of a first row of blastholes adjacent the void is greater than the burden distance of a second row of blastholes more remote from the void than such a first row; placing explosive charges into blastholes of at least the first and second row of blastholes for forming a first array of explosive charges and a second array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort.

Claim 37

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one limited void, a surface of the formation defining such a void providing at least one free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; forming an array of spaced apart blastholes in such a second portion of formation, the array comprising at least two rows of blastholes, wherein the burden distance of a first row of blastholes adjacent the void is greater than the burden distance of a second row of blastholes more remote from the void than such a first row; placing explosive charges into blastholes of at least the first and second row of blastholes for forming a first array of explosive charges and a second array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort.

Claim 46

A method of explosively expanding formation toward a void comprising the steps of: excavating a first portion of the formation to form a void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation which is to be explosively expanded toward such a void, extending away from such a free face; placing at least two arrays of spaced apart explosive charges in such a second portion of formation, the first array being closer to the free face than the second array, wherein the burden distance of the first array is greater than the burden distance of the second array, the equivalent scaled point charge depth of burial of the first array of explosive charges being substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges, the ratio of spacing distance to burden distance of the first array of explosive charges being about equal to the ratio of spacing distance to burden distance of the second array of explosive charges; and detonating the explosive charges for explosively expanding such a second portion of formation toward the void.

Claim 47

A method of explosively expanding formation toward a void comprising the steps of: excavating a first portion of the formation to form a void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation which is to be explosively expanded toward such a void, extending away from such a free face; placing at least two arrays of spaced apart explosive charges in such a second portion of formation, the first array being closer to the free face than the second array, wherein the burden distance of the first array is greater than the burden distance of the second array, the equivalent scaled point charge depth of burial of the first array of explosive charges being substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges, the ratio of spacing distance to burden distance of the first array of explosive charges being about equal to the ratio of spacing distance to burden distance of the second array of explosive charges; and detonating the explosive charges for explosively expanding such a second portion of formation toward the void.

Claim 50

A method of explosively expanding formation toward a void comprising the steps of: excavating a first portion of the formation to form a void, the surface of the formation defining such a void providing at least one free face extending throuh the formation and leaving a second portion of the formation extending away from such a free face, which second portion is to be explosively expanded toward such a void; placing at least two arrays of spaced apart explosive charges in such a second portion of formation, wherein each explosive charge of the first array of explosive charges has a scaled point charge depth of burial about equal to the equivalent scaled point charge depth of burial of such first array of explosive charges and each explosive charge of the second array of explosive charges has a scaled point charge depth of burial about equal to the equivalent scaled point charge depth of burial of the second array of explosive charges; and detonating the explosive charges for explosively expanding such a second portion of formation toward the void.

Claim 51

A method of explosively expanding formation toward a void comprising the steps of: excavating a first portion of the formation to form a void, the surface of the formation defining such a void providing at least one free face extending throuh the formation and leaving a second portion of the formation extending away from such a free face, which second portion is to be explosively expanded toward such a void; placing at least two arrays of spaced apart explosive charges in such a second portion of formation, wherein each explosive charge of the first array of explosive charges has a scaled point charge depth of burial about equal to the equivalent scaled point charge depth of burial of such first array of explosive charges and each explosive charge of the second array of explosive charges has a scaled point charge depth of burial about equal to the equivalent scaled point charge depth of burial of the second array of explosive charges; and detonating the explosive charges for explosively expanding such a second portion of formation toward the void.

Claim 54

A method of explosively expanding formation toward a limited void comprising the steps of: excavating a first portion of the formation to form a limited void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation extending away from such a free face, which second portion is to be explosively expanded toward such a void; forming at least one array of spaced apart blastholes in such a second portion of formation adjacent such a free face; placing at least two arrays of explosive charges into such blastholes, wherein the burden distance of a first array of such explosive charges is greater than the burden distance of a second array of such explosive charges and the first array of such explosive charges is closer to the free face than the second array of such explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the limited void.

Claim 55

A method of explosively expanding formation toward a limited void comprising the steps of: excavating a first portion of the formation to form a limited void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation extending away from such a free face, which second portion is to be explosively expanded toward such a void; forming at least one array of spaced apart blastholes in such a second portion of formation adjacent such a free face; placing at least two arrays of explosive charges into such blastholes, wherein the burden distance of a first array of such explosive charges is greater than the burden distance of a second array of such explosive charges and the first array of such explosive charges is closer to the free face than the second array of such explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the limited void.

Claim 62

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one vertically extending limited void, the surface of the formation defining such a void providing at least one free face extending vertically within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; forming an array of spaced apart blastholes in such a second portion of formation adjacent such a free face, the array comprising at least two substantially vertical rows of blastholes, each row extending substantially parallel to such a free face, wherein the burden distance of a first row of blastholes is greater than the burden distance of a second row of blastholes and the spacing distance of the second row of blastholes is less than the spacing distance of the first row of blastholes and wherein the first row of blastholes is closer to the free face than the second row of blastholes; placing explosive into blastholes of the first substantially vertical row of blastholes for forming a first array of explosive charges, and plaing explosive into blastholes of the second substantially vertical row of blastholes for forming a second array of explosive charges, the equivalent scaled point charge depth of burial of the first array of explosive charges being substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges; and detonating such explosive charges in a single round for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation forming an in situ oil shale retort.

Claim 63

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one vertically extending limited void, the surface of the formation defining such a void providing at least one free face extending vertically within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; forming an array of spaced apart blastholes in such a second portion of formation adjacent such a free face, the array comprising at least two substantially vertical rows of blastholes, each row extending substantially parallel to such a free face, wherein the burden distance of a first row of blastholes is greater than the burden distance of a second row of blastholes and the spacing distance of the second row of blastholes is less than the spacing distance of the first row of blastholes and wherein the first row of blastholes is closer to the free face than the second row of blastholes; placing explosive into blastholes of the first substantially vertical row of blastholes for forming a first array of explosive charges, and plaing explosive into blastholes of the second substantially vertical row of blastholes for forming a second array of explosive charges, the equivalent scaled point charge depth of burial of the first array of explosive charges being substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges; and detonating such explosive charges in a single round for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation forming an in situ oil shale retort.

Claim 67

A method of explosively expansing formation toward a void comprising the steps of: excavating a first portion of the formation to form a void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation which is to be explosively expanded toward such a void extending away from such a free face; placing explosive into such a second portion of formation; detonating such explosive for explosively expanding such a second portion of formation toward the void, the second portion of formation comprising at least first and second layers of unfragmented formation, such first and second layers being substantially parallel to such a free face wherein the volume of the second layer of formation is less than the volume of the first layer of formation, the explosive expansion of the second portion of formation toward the void comprising the steps of: initially expanding at least a portion of the first layer of unfragmented formation toward the void and thereafter expanding the second layer of unfragmented formation toward the void, wherein the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the first layer of formation is about equal to the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the second layer of formation.

Claim 68

A method of explosively expansing formation toward a void comprising the steps of: excavating a first portion of the formation to form a void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation which is to be explosively expanded toward such a void extending away from such a free face; placing explosive into such a second portion of formation; detonating such explosive for explosively expanding such a second portion of formation toward the void, the second portion of formation comprising at least first and second layers of unfragmented formation, such first and second layers being substantially parallel to such a free face wherein the volume of the second layer of formation is less than the volume of the first layer of formation, the explosive expansion of the second portion of formation toward the void comprising the steps of: initially expanding at least a portion of the first layer of unfragmented formation toward the void and thereafter expanding the second layer of unfragmented formation toward the void, wherein the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the first layer of formation is about equal to the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the second layer of formation.

Claim 74

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one void, the surface of the formation defining such a void providing at least one free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; forming an array of spaced apart blastholes in such a second portion of formation adjacent such a free face, the array comprising at least two substantially vertical rows of blastholes, wherein the burden distance of a first row of blastholes is greater than the burden distance of a second row of blastholes and the spacing distance of the second row of blastholes is less than the spacing distance of the first row of blastholes, and wherein the first row of blastholes is closer to the free face than the second row of blastholes; placing explosive into blastholes of the first substantially vertical row of blastholes for forming a first array of explosive charges, and placing explosive into blastholes of the second substantially vertical row of blastholes for forming a second array of explosive charges, the equivalent scaled point charge depth of burial of the first array of explosive charges being substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation forming an in situ oil shale retort.

Claim 75

A method for forming an in situ oil shale retort in a retort site within a subterranean formation containing oil shale, such an in situ oil shale retort containing a fragmented permeable mass of formation particles, such a fragmented mass having top, bottom, and side boundaries, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one void, the surface of the formation defining such a void providing at least one free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such a free face, such second portion to be explosively expanded toward such a void; forming an array of spaced apart blastholes in such a second portion of formation adjacent such a free face, the array comprising at least two substantially vertical rows of blastholes, wherein the burden distance of a first row of blastholes is greater than the burden distance of a second row of blastholes and the spacing distance of the second row of blastholes is less than the spacing distance of the first row of blastholes, and wherein the first row of blastholes is closer to the free face than the second row of blastholes; placing explosive into blastholes of the first substantially vertical row of blastholes for forming a first array of explosive charges, and placing explosive into blastholes of the second substantially vertical row of blastholes for forming a second array of explosive charges, the equivalent scaled point charge depth of burial of the first array of explosive charges being substantially equal to the equivalent scaled point charge depth of burial of the second array of explosive charges; and detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation forming an in situ oil shale retort.

Claim 79

A method of explosively expanding formation toward a limited void comprising the steps of: excavating a first portion of the formation to form a limited void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation which is to be explosively expanded toward such a void extending away from such a free face; placing explosive into such a second portion of formation; and detonating such explosive in a single round for explosively expanding such a second portion of formation toward the void, the second portion of formation comprising at least first and second layers of unfragmented formation, such first and second layers being substantially parallel to such a free face wherein the volume of the second layer of formation is less than the volume of the first layer of formation, the explosive expansion of the second portion of formation toward the void comprising the steps of: initially expanding at least a portion of the first layer of unfragmented formation toward the void and thereafter expanding the second layer of unfragmented formation toward the void, wherein the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the first layer of formation is about equal to the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the second layer of formation.

Claim 80

A method of explosively expanding formation toward a limited void comprising the steps of: excavating a first portion of the formation to form a limited void, the surface of the formation defining such a void providing at least one free face extending through the formation and leaving a second portion of the formation which is to be explosively expanded toward such a void extending away from such a free face; placing explosive into such a second portion of formation; and detonating such explosive in a single round for explosively expanding such a second portion of formation toward the void, the second portion of formation comprising at least first and second layers of unfragmented formation, such first and second layers being substantially parallel to such a free face wherein the volume of the second layer of formation is less than the volume of the first layer of formation, the explosive expansion of the second portion of formation toward the void comprising the steps of: initially expanding at least a portion of the first layer of unfragmented formation toward the void and thereafter expanding the second layer of unfragmented formation toward the void, wherein the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the first layer of formation is about equal to the equivalent scaled point charge depth of burial of the array of explosive charges used for explosively expanding the second layer of formation.

Claim 85

A method for recovering liquid and gaseous products from an in situ oil shale retort in a subterranean formation containing oil shale, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one void, a surface of the formation defining such a void providing at least a first free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such first free face, such second portion to be explosively expanded toward such a void; placing at least a first and a second array of spaced apart explosive charges in such a second portion of formation, the first array being closer to the first free face than the second array, wherein the burden distance of the first array measured from the first free face is greater than the burden distance of the second array measured from the first array of explosive charges; detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort; introducing gas into the fragmented permeable mass in the in situ oil shale retort for establishing a retorting zone in the fragmented mass wherein oil shale is retorted to produce gaseous and liquid products and for advancing the retorting zone through the fragmented mass; and withdrawing gaseous and liquid products from the retort.

Claim 86

A method for recovering liquid and gaseous products from an in situ oil shale retort in a subterranean formation containing oil shale, comprising the steps of: excavating a first portion of the formation from within the boundaries of the fragmented mass being formed to form at least one void, a surface of the formation defining such a void providing at least a first free face within the boundaries of the fragmented mass being formed, and leaving a second portion of the formation within the boundaries of such fragmented mass being formed and extending away from such first free face, such second portion to be explosively expanded toward such a void; placing at least a first and a second array of spaced apart explosive charges in such a second portion of formation, the first array being closer to the first free face than the second array, wherein the burden distance of the first array measured from the first free face is greater than the burden distance of the second array measured from the first array of explosive charges; detonating such explosive charges for explosively expanding such a second portion of formation toward the void to form a fragmented permeable mass of formation particles containing oil shale in the subterranean formation for forming an in situ oil shale retort; introducing gas into the fragmented permeable mass in the in situ oil shale retort for establishing a retorting zone in the fragmented mass wherein oil shale is retorted to produce gaseous and liquid products and for advancing the retorting zone through the fragmented mass; and withdrawing gaseous and liquid products from the retort.