Multi-stage method of operating an in situ oil shale retort

In a method of processing oil shale in an in situ oil shale retort in a subterranean formation containing oil shale, said in situ retort being in the form of a cavity containing a fragmented permeable mass of formation particles containing oil shale wherein a processing gas is passed through the cavity for causing a processing zone to pass through the cavity, the improvement comprising:

• passing the processing gas through only a first portion of the cavity during a first stage of operation of the retort;
• passing the processing gas through only a second portion of the cavity during a later stage of operation of the retort, the second portion being in a downsteam direction from the first portion;
• and
• passing the processing gas through both the first and second portions during a transition operation between the first and the later stage of operation.

In a method of operating an elongated, vertically extending in situ oil shale retort in a subterranean formation containing oil shale, said retort being in the form of a subterranean cavity containing a fragmented permeable mass of formation particles containing oil shale, by heating the mass of particles in the in situ oil shale retort to form a processing zone and advancing the processing zone downwardly through the in situ oil shale retort, the improvement comprising:

• initially introducing processing gas at an upper portion of the cavity and withdrawing off gas from an intermediate portion between the top and the bottom of the cavity while the processing zone is between the upper portion and the intermediate portion;
• temporarily introducing processing gas at the upper portion of the cavity and withdrawing off gas from the lower portion of the cavity while the processing zone is in the intermediate portion;
• and
• thereafter introducing processing gas at the intermediate portion and withdrawing off gas from a lower portion of the cavity while the processing zone is between the intermediate portion and the lower portion.

An in situ oil shale retort in a subterranean formation containing oil shale comprising:

• a cavity containing a fragmented permeable mass of formation particles containing oil shale having a predetermined average void fraction, an intermediate portion of the mass of formation particles between the ends of the cavity having a void fraction greater than the predetermined average void fraction;
• means for introducing processing gas at one end of the cavity;
• means for withdrawing off gas from the other end of the cavity;
• and
• means in fluid communication with the intermediate portion of the mass of formation particles having greater than average void fraction for alternatively withdrawing off gas from the intermediate portion and introducing processing gas to the intermediate portion.

A method of processing oil shale in an in situ oil shale retort in a subterranean formation containing oil shale, said retort comprising a cavity containing a fragmented permeable mass of formation particles containing oil shale, comprising the steps of:

• during a first stage of processing introducing a processing gas at one end of the retort and withdrawing off gas from an intermediate portion of the retort between its ends;
• and
• thereafter during a second stage of processing introducing a processing gas at an intermediate portion of the retort between its ends and withdrawing off gas from the other end;
• and wherein
• the retort has a single intermediate portion where off gas is withdrawn during the first stage and processing gas is introduced during the second stage;
• and
• further comprising the step of introducing processing gas at one end and withdrawing off gas from the other end between the first and second stages of processing.

A method of retorting oil shale in an in situ oil shale retort comprising the steps of:

• forming an in situ oil shale retort comprising a cavity in the subterranean formation containing oil shale, the cavity containing a fragmented permeable mass of formation particles containing oil shale;
• forming a gas inlet to the cavity;
• forming a gas outlet from the cavity;
• forming at least one intermediate access to the cavity between the gas inlet and the gas outlet;
• establishing a processing zone in the mass of formation particles near the gas inlet;
• introducing processing gas into the cavity through the gas inlet and withdrawing off gas from the cavity through an intermediate access during a first stage of processing for moving the processing zone through a first portion of the mass of formation particles between the gas inlet and the intermediate access;
• and
• introducing processing gas to the cavity through an intermediate access and withdrawing off gas from the cavity through the gas outlet during a later stage of processing following the first stage for moving the processing zone through another portion of the mass of formation particles.