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US4440447A
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Method for forming an in situ oil shale retort with explosive expansion towards a horizontal free face
Assignee: Occidental Oil Shale Inc
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Filing: 1982-03-12
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Granted: 1984-04-03
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Expires: 2002-03-12
Abstract
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. Explosive in each outer explosive charge extends nearer the free face toward which unfragmented formation is to be explosively expanded than any portion of the explosive in a central explosive charge. Additionally, each outer explosive charge has a scaled depth of burial which is no greater than the scaled depth of burial of each central explosive charge. The explosive charges are thereafter detonated for explosively expanding the zone of unfragmented formation toward the void, forming the fragmented permeable mass of formation particles in the in situ oil shale retort.
Inventors
- 👤 Thomas E. Ricketts
- 👤 John E. Shaler
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 20:11
CPC Classifications
E; E21; E21B; E21B43/00; E21B43/16; E21B43/24; E21B43/243; E21B43/247; E21B43/248; E21C; E21C41/00; E21C41/16; E21C41/24
Claims Analysis
Total Claims: 56
Claim 1
Independent Claim
246 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: forming at least one void within the retort site in the subterranean formation, the void bounded by generally vertical side walls and zones of unfragmented formation above and below, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of spaced apart explosive charges in the zone of unfragmented formation, the array of explosive charges comprising at least one central explosive charge spaced apart from the side boundaries and at least one outer explosive charge closer to an adjacent side boundary than such a central explosive charge the actual depth of burial of each such outer explosive charge being less than the actual depth of burial of each such central explosive charge, and the scaled depth of burial of each such outer explosive charge being not more than the scaled depth of burial of each such central explosive charge; and detonating the array of explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 2
Independent Claim
246 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: forming at least one void within the retort site in the subterranean formation, the void bounded by generally vertical side walls and zones of unfragmented formation above and below, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of spaced apart explosive charges in the zone of unfragmented formation, the array of explosive charges comprising at least one central explosive charge spaced apart from the side boundaries and at least one outer explosive charge closer to an adjacent side boundary than such a central explosive charge the actual depth of burial of each such outer explosive charge being less than the actual depth of burial of each such central explosive charge, and the scaled depth of burial of each such outer explosive charge being not more than the scaled depth of burial of each such central explosive charge; and detonating the array of explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 3
Dependent Claim
47 words
The method according to claim 1 wherein each outer and central explosive charge has a first portion remote from said void wherein the first portion of each such outer charge is about the same distance from said void as the first portion of each such central charge.
Claim 4
Dependent Claim
60 words
The method according to claim 2 wherein each such central charge extends into the zone of unfragmented formation to be explosively expanded a distance equal to about one-half the thickness of such zone and each outer explosive charge extends into such zone to be explosively expanded a distance equal to about two-thirds to about three-fourths the thickness of such zone.
Claim 5
Dependent Claim
24 words
The method according to claim 1 wherein the distance between adjacent outer explosive charges is less than the distance between adjacent central explosive charges.
Claim 6
Dependent Claim
32 words
The method according to claim 1 wherein the distance between an outer explosive charge and an adjacent central explosive charge is about equal to the distance between the adjacent central explosive charges.
Claim 7
Dependent Claim
25 words
The method according to claim 1 wherein the distance between adjacent central explosive charges is about equal to the distance between adjacent outer explosive charges.
Claim 8
Dependent Claim
52 words
The method according to claim 6 comprising positioning outer explosive charges within such zone of unfragmented formation to be explosively expanded such that the distance from each outer explosive charge to the closest wall of the retort adjacent thereto is not more than about one-half the distance between adjacent outer explosive charges.
Claim 9
Dependent Claim
22 words
The method according to claim 1 wherein the outer explosive charges vary along their length in energy per unit volume of charge.
Claim 10
Dependent Claim
49 words
The method according to claim 8 wherein the energy per unit volume of charge of each such outer explosive charge is lower in a portion of the outer explosive charge nearer the void and is higher in a portion of the outer explosive charge more remote from the void.
Claim 11
Independent Claim
273 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, the in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation, comprising the steps of: forming at least one void within the retort site in the subterranean formation, the void bounded by generally vertical side walls of unfragmented formation and zones of unfragmented formation above and below, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of spaced apart substantially vertical blastholes in the zone of unfragmented formation, the array of blastholes comprising central blastholes remote from the side boundaries and outer blastholes spaced apart from and about the central blastholes; loading each of the central blastholes with explosive to thereby form a plurality of substantially vertica columnar central explosive charges; loading each of the outer blastholes with explosvie to thereby form a plurality of substantially vertical columnar outer explosive charges, the scaled depth of burial of each such outer explosive charge being less than the scaled depth of burial of each such central explosive charge and the powder factor of each such outer explosive charge being greater than the powder factor of each such central explosive charge; and detonating the explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 12
Independent Claim
273 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort in a retort site in a subterranean formation containing oil shale, the in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation, comprising the steps of: forming at least one void within the retort site in the subterranean formation, the void bounded by generally vertical side walls of unfragmented formation and zones of unfragmented formation above and below, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of spaced apart substantially vertical blastholes in the zone of unfragmented formation, the array of blastholes comprising central blastholes remote from the side boundaries and outer blastholes spaced apart from and about the central blastholes; loading each of the central blastholes with explosive to thereby form a plurality of substantially vertica columnar central explosive charges; loading each of the outer blastholes with explosvie to thereby form a plurality of substantially vertical columnar outer explosive charges, the scaled depth of burial of each such outer explosive charge being less than the scaled depth of burial of each such central explosive charge and the powder factor of each such outer explosive charge being greater than the powder factor of each such central explosive charge; and detonating the explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 13
Dependent Claim
34 words
The method according to claim 10 wherein each such outer explosive charge has an actual depth of burial which is not more than the actual depth of burial of each such central explosive charge.
Claim 14
Dependent Claim
25 words
The method according to claim 11 wherein each outer explosive charge has a length which is greater than the length of each central explosive charge.
Claim 15
Dependent Claim
29 words
The method according to claim 12 wherein the length of each such central explosive charge is about one-half the thickness of the zone of unfragmented formation being explosively expanded.
Claim 16
Dependent Claim
33 words
The method according to claim 13 wherein the length of each such outer explosive charge is from about two-thirds to about three-fourths the thickness of the zone of unfragmented formation being explosively expanded.
Claim 17
Dependent Claim
25 words
The method according to claim 12 wherein each such outer explosive charge has a diameter less than the diameter of each such central explosive charge.
Claim 18
Dependent Claim
29 words
The method according to claim 10 wherein a portion of each such outer explosive charge is closer to the void than any portion of any such central explosive charge.
Claim 19
Dependent Claim
28 words
The method according to claim 10 wherein the powder factor of each such outer explosive charge is about twice the powder factor of each such central explosive charge.
Claim 20
Dependent Claim
23 words
The method according to claim 10 wherein the distance between adjacent central blastholes is about equal to the distance between adjacent outer blastholes.
Claim 21
Dependent Claim
51 words
The method according to claim 10 comprising forming outer blastholes at a location within the zone of unfragmented formation to be explosively expanded such that the distance from each outer blasthole to an adjacent side boundary of the retort is not more than about one-half the distance between adjacent central blastholes.
Claim 22
Dependent Claim
34 words
The method according to claim 10 comprising initiating detonation of the outer explosive charges at about a point in the charge relatively nearer the void than the point of detonation of the central charges.
Claim 23
Independent Claim
271 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: (a) forming at least one void within the retort site in the subterranean formation, leaving zones of unfragmented formation above and below such a void, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; (b) forming an array of horizontally spaced apart substantially vertical blastholes in the zone of unfragmented formation, the array of blastholes comprising a plurality of central blastholes spaced apart from the side boundaries and a plurality of outer blastholes spaced around the central blastholes; (c) loading each central blasthole with explosive to thereby form a vertical columar central explosive charge in each central blasthole; (d) loading each outer blasthole with explosive to thereby form vertically spaced apart first and second columnar explosive charges in each outer blasthole, a portion of each such first outer explosive charge being closer to the void than any portion of each such central explosive charge is to the void, each such second outer explosive charge spaced more remote from the void than each such first outer explosive charge; and (e) detonating the explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 24
Independent Claim
271 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: (a) forming at least one void within the retort site in the subterranean formation, leaving zones of unfragmented formation above and below such a void, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; (b) forming an array of horizontally spaced apart substantially vertical blastholes in the zone of unfragmented formation, the array of blastholes comprising a plurality of central blastholes spaced apart from the side boundaries and a plurality of outer blastholes spaced around the central blastholes; (c) loading each central blasthole with explosive to thereby form a vertical columar central explosive charge in each central blasthole; (d) loading each outer blasthole with explosive to thereby form vertically spaced apart first and second columnar explosive charges in each outer blasthole, a portion of each such first outer explosive charge being closer to the void than any portion of each such central explosive charge is to the void, each such second outer explosive charge spaced more remote from the void than each such first outer explosive charge; and (e) detonating the explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 25
Dependent Claim
45 words
The method according to claim 21 wherein each such first outer explosive charge has a first scaled depth of burial and each such second outer explosive charge has a second scaled depth of burial, the first and second scaled depth of burial being about equal.
Claim 26
Dependent Claim
34 words
The method according to claim 22 wherein the scaled depth of burial of each such first outer explosive charge is no more than the scaled depth of burial of each such central explosive charge.
Claim 27
Dependent Claim
45 words
The method according to claim 22 comprising detonating the explosive charges in a time delay sequence in a single round wherein the first outer explosive charges are detonated and, after a time delay, the second outer explosive charges and the central explosive charges are detonated.
Claim 28
Dependent Claim
41 words
The method according to claim 21 comprising detonating the explosive charges in a time delay sequence in a single round comprising detonating the central explosive charges, then detonating the first outer explosive charges, and thereafter detonating the second outer explosive charges.
Claim 29
Dependent Claim
39 words
The method according to claim 21 wherein the end remote from the void of each second outer explosive charge is about the same distance from the void as the end remote from the void of each central explosive charge.
Claim 30
Dependent Claim
327 words
A mehtod for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: forming at least one void within the retort site in the subterranean formation, leaving zones of unfragmented formation above and below such a void, the side walls of the void being a portion of the side boundaries of the retort being formed, with the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of horizontally spaced apart substantially vertical columnar explosive charges in the zone of unfragmented formation for explosively expanding said zone of unfragmented formation toward its substantially horizontal free face adjacent the void, the array of explosive charges comprising a plurality of central explosive charges remote from the side boundaries and a plurality of outer explosive charges horizontally spaced apart from the central explosive charges and around the central explosive charges, the outer explosive charges being horizontally spaced apart from said walls of the void less than about one-half the distance between adjacent central explosive charges, at least a portion of the explosive comprising each such outer explosive charge being closer to the substantially horizontal free face toward which the zone of unfragmented formation is being explosively expanded than any portion of the explosive comprising each such central explosive charge, and the scaled depth of burial of each such outer explosive charge being not more than the scaled depth of burial of each such central explosive charge; and detonating the central and outer explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 31
Dependent Claim
327 words
A mehtod for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: forming at least one void within the retort site in the subterranean formation, leaving zones of unfragmented formation above and below such a void, the side walls of the void being a portion of the side boundaries of the retort being formed, with the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of horizontally spaced apart substantially vertical columnar explosive charges in the zone of unfragmented formation for explosively expanding said zone of unfragmented formation toward its substantially horizontal free face adjacent the void, the array of explosive charges comprising a plurality of central explosive charges remote from the side boundaries and a plurality of outer explosive charges horizontally spaced apart from the central explosive charges and around the central explosive charges, the outer explosive charges being horizontally spaced apart from said walls of the void less than about one-half the distance between adjacent central explosive charges, at least a portion of the explosive comprising each such outer explosive charge being closer to the substantially horizontal free face toward which the zone of unfragmented formation is being explosively expanded than any portion of the explosive comprising each such central explosive charge, and the scaled depth of burial of each such outer explosive charge being not more than the scaled depth of burial of each such central explosive charge; and detonating the central and outer explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 32
Dependent Claim
26 words
The method according to claim 27 comprising forming the outer explosive charges with a powder factor higher than the powder factor of the central explosive charges.
Claim 33
Independent Claim
207 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a subterranean formation containing oil shale, comprising the steps of: forming at least one generally horizontally extending void in the subterranean formation, leaving zones of unfragmented formation above and below such a void; forming an array of horizontally spaced apart substantially vertical blastholes in at least one of the zones of unfragmented formation, the array of blastholes comprising a plurality of central blastholes and a plurality of outer blastholes; loading each of the central blastholes with explosive, forming a plurality of vertical columnar central explosive charges; loading each of the outer blastholes with explosive, forming a plurality of vertical columnar outer explosive charges, each of the outer explosive charges having a different energy per unit volume of charge in a first portion of the length of the charge than the energy per unit volume of charge in a second portion of the length of the charge; and detonating the explosive charges for explosively expanding such a zone of unfragmented formation toward the void for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 34
Independent Claim
207 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a subterranean formation containing oil shale, comprising the steps of: forming at least one generally horizontally extending void in the subterranean formation, leaving zones of unfragmented formation above and below such a void; forming an array of horizontally spaced apart substantially vertical blastholes in at least one of the zones of unfragmented formation, the array of blastholes comprising a plurality of central blastholes and a plurality of outer blastholes; loading each of the central blastholes with explosive, forming a plurality of vertical columnar central explosive charges; loading each of the outer blastholes with explosive, forming a plurality of vertical columnar outer explosive charges, each of the outer explosive charges having a different energy per unit volume of charge in a first portion of the length of the charge than the energy per unit volume of charge in a second portion of the length of the charge; and detonating the explosive charges for explosively expanding such a zone of unfragmented formation toward the void for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 35
Dependent Claim
46 words
The method according to claim 29 wherein each such outer explosive charge has a higher energy per unit volume in a portion of the charge more remote from the void and a lower energy per unit volume in a portion of the charge nearer the void.
Claim 36
Dependent Claim
37 words
The method according to claim 29 comprising initiating detonation of such an outer explosive charge at a point in the charge nearer the void than the point of initiation of detonation of each such central explosive charge.
Claim 37
Dependent Claim
33 words
The method according to claim 29 wherein the actual depth of burial of each such outer explosive charge is no more than the actual depth of burial of each such central explosive charge.
Claim 38
Dependent Claim
32 words
The method according to claim 29 wherein a portion of each such outer explosive charge is nearer the void than any portion of each such central explosive charge is to the void.
Claim 39
Independent Claim
194 words
A method for explosively expanding formation toward a substantially horizontally extending free face of unfragmented formation in a subterranean formation, comprising the steps of: forming at least one void in the subterranean formation, such a void bounded by generally vertical side walls and horizontally extending zones of unfragmented formation above and below, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of horizontally spaced apart substantially vertical columnar explosive charges in the zone of unfragmented formation, explosive charges nearest the side walls of the void extending closer to the substantially horizontal free face of the zone of unfragmented formation than explosive charges more remote from the side walls of the void, the scaled depth of burial of the explosive charges nearest the side walls of the void being less than the scaled depth of burial of the explosive charges more remote from the side walls of the void; and detonating the explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face.
Claim 40
Independent Claim
194 words
A method for explosively expanding formation toward a substantially horizontally extending free face of unfragmented formation in a subterranean formation, comprising the steps of: forming at least one void in the subterranean formation, such a void bounded by generally vertical side walls and horizontally extending zones of unfragmented formation above and below, the surface adjacent the void of at least one of such zones of unfragmented formation forming a substantially horizontal free face towards which such a zone of unfragmented formation is to be expanded; forming an array of horizontally spaced apart substantially vertical columnar explosive charges in the zone of unfragmented formation, explosive charges nearest the side walls of the void extending closer to the substantially horizontal free face of the zone of unfragmented formation than explosive charges more remote from the side walls of the void, the scaled depth of burial of the explosive charges nearest the side walls of the void being less than the scaled depth of burial of the explosive charges more remote from the side walls of the void; and detonating the explosive charges for explosively expanding the zone of unfragmented formation toward its substantially horizontal free face.
Claim 41
Dependent Claim
38 words
The method according to claim 34 wherein the explosive charges nearest the side walls of the void have a higher powder factor than the powder factor of explosive charges more remote from the side walls of the void.
Claim 42
Dependent Claim
38 words
The method according to claim 35 wherein the distance between adjacent explosive charges nearest the side walls of the void is less than the distance between adjacent explosive charges more remote from the side walls of the void.
Claim 43
Dependent Claim
39 words
The method according to claim 34 wherein the distance between adjacent explosive charges nearest the side walls of the void is about equal to the distance between adjacent explosive charges more remote from the side walls of the void.
Claim 44
Dependent Claim
49 words
The method according to claim 37 wherein the distance between such an explosive charge nearest a side wall of the void and an adjacent explosive charge more remote from such a side wall is about equal to the distance between adjacent explosive charges more remote from the side walls.
Claim 45
Dependent Claim
31 words
The method according to claim 34 wherein the explosive charges nearest the side walls of the void are longer than explosive charges more remote from the side walls of the void.
Claim 46
Dependent Claim
46 words
The method according to claim 39 wherein each of the explosive charges in such a zone of unfragmented formation has a far end remote from the free face and each far end is at about the same distance from the void as each other far end.
Claim 47
Independent Claim
250 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: forming at least one void within the retort site in the subterranean formation, such a void bounded by generally vertical side walls and horizontally extending zones of unfragmented formation above and below the void, the surface adjacent the void of each such zone of unfragmented formation forming a substantially horizontal free face towards which unfragmented formation is to be expanded; forming an array of spaced apart explosive charges in each of the zones of unfragmented formation, such an array of explosive charges comprising at least one central explosive charge horizontally spaced apart from the side boundaries and at least one outer explosive charge horizontally spaced apart from and around the central charges, the actual depth of burial of each such outer explosive charge being less than the actual depth of burial of each such central explosive charge, and the scaled depth of burial of each such outer explosive charge being not more than the scaled depth of burial of each such central explosive charge; and detonating the array of explosive charges in each such zone of unfragmented formation for explosively expanding each zone toward its respective substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 48
Independent Claim
250 words
A method for forming a fragmented permeable mass of formation particles in an in situ oil shale retort having top, bottom, and side boundaries of unfragmented formation in a retort site in a subterranean formation containing oil shale, the method comprising the steps of: forming at least one void within the retort site in the subterranean formation, such a void bounded by generally vertical side walls and horizontally extending zones of unfragmented formation above and below the void, the surface adjacent the void of each such zone of unfragmented formation forming a substantially horizontal free face towards which unfragmented formation is to be expanded; forming an array of spaced apart explosive charges in each of the zones of unfragmented formation, such an array of explosive charges comprising at least one central explosive charge horizontally spaced apart from the side boundaries and at least one outer explosive charge horizontally spaced apart from and around the central charges, the actual depth of burial of each such outer explosive charge being less than the actual depth of burial of each such central explosive charge, and the scaled depth of burial of each such outer explosive charge being not more than the scaled depth of burial of each such central explosive charge; and detonating the array of explosive charges in each such zone of unfragmented formation for explosively expanding each zone toward its respective substantially horizontal free face for forming a fragmented permeable mass of formation particles in the in situ oil shale retort.
Claim 49
Dependent Claim
46 words
The method according to claim 41 wherein each such outer and central explosive charge has a first portion remote from the void wherein the first portion of each outer charge is about the same distance from the void as the first portion of each central charge.
Claim 50
Dependent Claim
52 words
The method according to claim 42 wherein each central charge extends into such a zone of unfragmented formation a distance equal to about one-half the thickness of the zone and each outer explosive charge extends into the zone a distance equal to about two-thirds to about three-fourths the thickness of the zone.
Claim 51
Dependent Claim
24 words
The method according to claim 41 wherein the distance between adjacent outer explosive charges is less than the distance between adjacent central explosive charges.
Claim 52
Dependent Claim
32 words
The method according to claim 41 wherein the distance between an outer explosive charge and an adjacent central explosive charge is about equal to the distance between the adjacent central explosive charges.
Claim 53
Dependent Claim
25 words
The method according to claim 41 wherein the distance between adjacent central explosive charges is about equal to the distance between adjacent outer explosive charges.
Claim 54
Dependent Claim
49 words
The method according to claim 46 comprising positioning outer explosive charges within such a zone of unfragmented formation such that the distance from each outer explosive charge to the closest wall of the retort adjacent thereto is not more than about one-half the distance between adjacent outer explosive charges.
Claim 55
Dependent Claim
22 words
The method according to claim 41 wherein the outer explosive charges vary in energy per unit volume of charge along their length.
Claim 56
Dependent Claim
49 words
The method according to claim 48 wherein the energy per unit volume of charge of each such outer explosive charge is lower in a portion of the outer explosive charge nearer the void and is higher in a portion of the outer explosive charge more remote from the void.
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USPTO Annuity & Maintenance Windows
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| 3.5 Years (Year 4) | 1987-04-03 | 1987-10-03 | 1988-04-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-04-03 | 1991-10-03 | 1992-04-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-04-03 | 1995-10-03 | 1996-04-03 | $7700.00 | Window Closed / Lapsed |