Method for flattening the combustion zone in an in situ oil shale retort by the addition of fuel

In a method for controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the method comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen-supplying gas to the fragmented permeable mass through the retort inlet for sustaining the primary combustion zone, the improvement comprising:
• for a second period of time introducing into the retort a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby forming a secondary combustion zone at a first location in the fragmented permeable mass upstream of the primary combustion zone;
• and
• during the second period of time introducing into the retort a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby moving the secondary combustion zone to a second location in the fragmented permeable mass.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen-supplying gas to the fragmented mass through the retort inlet for sustaining the primary combustion zone and advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to the fragmented mass to establish a secondary combustion zone at a first location in the fragmented mass and sustain the primary combustion zone;
• and
• during the second period of time introducing a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to the fragmented mass to sustain the primary combustion zone and move the secondary combustion zone to a second location in the fragmented mass.

The method for establishing and controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the fragmented mass having a gas flow path between a retort inlet and a retort outlet, the method comprising the steps of:

• establishing a primary combustion zone in the in situ oil shale retort;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture containing fuel and at least sufficient oxygen for combustion of the fuel into the retort on the trailing side of the primary combustion zone for establishing a secondary combustion zone in the fragmented mass at a first location in the fragmented mass upstream from the primary combustion zone;
• and
• during the second period of time progressively reducing the ignition temperature of the second retort inlet mixture for moving the secondary combustion zone toward a second location upstream from the first location.

A method for establishing and controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the fragmented mass having a gas flow path between a retort inlet and a retort outlet, the method comprising the steps of:

• establishing a primary combustion zone in the in situ oil shale retort;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture containing fuel and at least sufficient oxygen for combustion of the fuel into the retort on the trailing side of the primary combustion zone for establishing a secondary combustion zone in the fragmented mass at a first location in the fragmented mass upstream from the primary combustion zone;
• and
• during the second period of time progressively moving the secondary combustion zone upstream from the first location in the fragmented mass.

A method for establishing and controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the fragmented mass having a gas flow path between a retort inlet and a retort outlet, the method comprising the steps of:

• establishing a primary combustion zone in the in situ oil shale retort;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture containing fuel and at least sufficient oxygen for combustion of the fuel into the retort on the trailing side of the primary combustion zone for establishing a secondary combustion zone in the fragmented mass at a first location in the fragmented mass upstream from the primary combustion zone;
• during the second period of time progressively moving the secondary combustion zone to a second location upstream from the first location in the fragmented mass by progressively reducing the ignition temperature of the second retort inlet mixture;
• and
• maintaining the secondary combustion zone at the second location until the percentage of oxygen in off gas from the retort reaches a predetermined value.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• introducing a retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to establish a secondary combustion zone in the fragmented permeable mass upstream of the primary combustion zone;
• and
• extinguishing the secondary combustion zone by discontinuing introduction of the fuel in the retort inlet mixture when the percentage of oxygen in off gas from the retort reaches a predetermined value.

In a method for controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the method comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for sustaining the primary combustion zone, the improvement comprising:
• for a second period of time introducing into the retort a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, the second retort inlet mixture having an ignition temperature no greater than the primary combustion zone temperature so that combustion of the second retort inlet mixture occurs at a first location in the fragmented permeable mass of particles forming a secondary combustion zone at such a first location in the fragmented permeable mass of particles upstream of the primary combustion zone;
• and
• during the second period of time introducing into the retort a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby moving the secondary combustion zone to a second location in the fragmented mass.

In a method for controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the method comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for sustaining the primary combustion zone, the improvement comprising:
• for a second period of time introducing into the retort a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby forming a secondary combustion zone at a first location in the fragmented mass;
• and
• during the second period of time progressively increasing the proportion of fuel in the second retort inlet mixture for progressively moving the secondary combustion zone from the first location to a second location in the fragmented permeable mass.

In a method for controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the method comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for sustaining the primary combustion zone, the improvement comprising:
• for a second period of time introducing into the retort a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby forming a secondary combustion zone at a first location in the fragmented mass;
• and
• during the second period of time introducing into the retort a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, wherein the ignition temperature of the third retort inlet mixture is less than the ignition temperature of the second retort inlet mixture, thereby moving the secondary combustion zone to a second location in the fragmented mass.

In a method for controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the method comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for sustaining the primary combustion zone, the improvement comprising:
• for a second period of time introducing into the retort a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby forming a secondary combustion zone at a first location in the fragmented mass;
• and
• during the second period of time introducing into the retort a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby moving the secondary combustion zone to a second location in the fragmented mass, wherein the fuel to oxygen ratio of the third retort inlet mixture is different from the fuel to oxygen ratio of the second retort inlet mixture.

In a method for controlling the location of a secondary combustion zone in an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, the method comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented permeable mass through the retort inlet for sustaining the primary combustion zone, the improvement comprising:
• for a second period of time introducing into the retort a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, thereby forming a secondary combustion zone at a first location in the fragmented mass;
• and
• during the second period of time introducing into the retort a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, wherein the chemical composition of the third retort inlet mixture is different from the chemical composition of the second retort inlet mixture, thereby moving the secondary combustion zone to a second location in the fragmented mass.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented mass through the retort inlet for sustaining the primary combustion zone and advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel, wherein the second retort inlet mixture has an ignition temperature no greater than the maximum primary combustion zone temperature so that combustion of the second retort inlet mixture occurs to establish a secondary combustion zone at a first location in the fragmented mass upstream of the primary combustion zone;
• and
• during the second period of time introducing a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to move the secondary combustion zone to a second location in the fragmented mass.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented mass through the retort inlet for sustaining the primary combustion zone and advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to establish a secondary combustion zone at a first location in the fragmented mass;
• and
• during the second period of time progressively increasing the proportion of fuel in the second retort inlet mixture for progressively moving the secondary combustion zone from the first location to a second location in the fragmented permeable mass.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented mass through the retort inlet for sustaining the primary combustion zone and advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to establish a secondary combustion zone at a first location in the fragmented mass;
• and
• during the second period of time introducing a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel at a second location in the fragmented mass, upstream from the first location, wherein the ignition temperature of the third retort inlet mixture is less than the ignition temperature of the second retort inlet mixture, to move the secondary combustion zone to the second location in the fragmented mass.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented mass through the retort inlet for sustaining the primary combustion zone and advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to establish a secondary combustion zone at a first location in the fragmented mass;
• and
• during the second period of time introducing a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel at a second location in the fragmented mass, upstream from the first location, to move the secondary combustion zone to the second location in the fragmented mass, and wherein the fuel to oxygen ratio of the third retort inlet mixture is different from the fuel to oxygen ratio of the second retort inlet mixture.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• for a first period of time introducing a first retort inlet mixture comprising an oxygen supplying gas to the fragmented mass through the retort inlet for sustaining the primary combustion zone and advancing the primary combustion zone through the fragmented mass;
• for a second period of time introducing a second retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to establish a secondary combustion zone at a first location in the fragmented mass upstream of the primary combustion zone;
• and
• during the second period of time introducing a third retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel at a second location in the fragmented mass, upstream from the first location, to move the secondary combustion zone to the second location in the fragmented mass, and wherein the chemical composition of the third retort inlet mixture is different from the chemical composition of the second retort inlet mixture.

A method for operating an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale comprising the steps of:

• establishing a primary combustion zone in a portion of the fragmented permeable mass near a retort inlet;
• introducing a retort inlet mixture comprising fuel and at least sufficient oxygen for combustion of the fuel to establish a secondary combustion zone in the fragmented permeable mass;
• and
• extinguishing the secondary combustion zone by discontinuing introduction of the fuel in the retort inlet mixture when the percentage of oxygen in off gas from the retort reaches a predetermined value, wherein the predetermined value of oxygen in off gas from the retort is less than about 0.8%.