Transient response process for detecting in situ retorting conditions

A process for use in underground retorting of oil shale, comprising the steps of:

• igniting a flame front across a generally upright, modified in situ retort;
• liberating shale oil and carbon dioxide from said raw oil shale in a mineral decomposition zone with heat generated by said flame front;
• supporting said flame front with a feed gas containing air and a diluent;
• changing the amount of air in said feed gas;
• and
• determining the depth of said mineral decomposition zone by monitoring the amount of said carbon dioxide liberated in response to said change.

A process for use in underground retorting oil shale, comprising the steps of:

• igniting a flame front across a generally upright, modified in situ retort;
• liberating shale oil and hydrogen saturated gases from said raw oil shale in a kerogen decomposition zone with heat generated by said flame front;
• supporting said flame front with a feed gas containing air and a diluent;
• changing the amount of air in said feed gas;
• and
• determining the depth of said kerogen decomposition zone by monitoring the amount of said hydrogen saturated gases liberated in response to said, change.

A process for use in underground retorting of oil shale, comprising the steps of:

• igniting a flame front across a generally upright, modified in situ retort to form a hot zone;
• liberating shale oil and off gases from said raw oil shale in said hot zone with heat emitted from said flame front, leaving retorted oil shale containing residual carbon;
• combusting said residual carbon on said retorted oil shale to form spent oil shale;
• advancing said flame front-downwardly through a portion of said raw oil shale;
• supporting said flame front with a feed gas consisting essentially of steam and air;
• changing the proportion of said steam and said air in said feed gas while supporting said flame front;
• analyzing the composition of said off gases with analyzing means consisting essentially of a gas chromatograph and a gas detector;
• and
• determining the location and depth of said hot zone by measuring the temperature of said off gases with a thermometer and by measuring the time it takes for the composition of the off gases to change after the proportion of steam and air in said feed gas has been changed with timing means selected from the group consiting essentially of a clock and a stopwatch.