Farouq Ali's characterization of ISC: the most tantalizing EOR process.
Dr. Ashok Singhal's characterization of ISC: Too simple to describe in general, but too complex to describe in detail.
My characterization of ISC: In some applications ISC is of a gordian complexity. My two criteria for success (a necessary condition and a sufficient condition must be met): The necessary condition is to burn efficiently (very good oxygen utilization efficiency) and the sufficient condition is to produce oil at an economic air-oil ratio.
A) ISC for Heavy Oil Recovery
Two phases of the ISC process: Unlike all EOR process, ignition has to be performed first, hence two phases: ignition (generation of the ISC front in the oil reservoir, near the injection well) and the propagation of the ISC front towards the surrounding production wells. Ignition procedures:
- Using artificial devices (gas burners and electric heaters)
- Spontaneous ignition
- Enhanced spontaneous ignition (chemically enhanced and/or steam-supported)
When choosing the ignition method, the following parameters are taken into account:
- Reservoir temperature
- Oxidability characteristics of the oil-rock couple
- Depth of reservoir
Two kinds of ISC processes:
- Forward ISC (which can be dry or wet)
- Reverse ISC
Note 1: Only forward ISC is commercially applied. General rule for forward ISC application: Apply pre-heating (if the oil viscosity > 1,500-2,000 cp); pre-heating is usually done by cyclic steam stimulation (CSS).
Fluid saturation and temperature profile for dry forward ISC (picture 1) clearly shows that most of the generated heat remains behind the ISC front and therefore does not contribute to oil heating and its viscosity decrease. That’s why the wet ISC was designed; to transfer some of this heat to the region ahead of the ISC front, as seen in fluid saturation and temperature profile for wet forward ISC (picture 2). In practice, both dry and wet ISC are segregated, hence the term segregated ISC.
C) Essential information on routine laboratory testing (in view of field testing)
For evaluation of applicability of ISC in a certain field, one could consider 3 main laboratory tests, namely: Combustion Tube (CT) tests, Ramped Temperature Oxidation (RTO) tests and Accelerated Rate Calorimetry (ARC) tests. The kinetics of oxidation [high temperature oxidation (HTO) and low temperature oxidation(LTO)] is investigated using RTO and ARC tests.
What is each test simulating and what information is providing:
ARC and RTO tests provide information on chemical reactivity of oil in porous medium. The oxidation (more generally the chemical/physical transformations) of an infinitesimal volume of oil reservoir when the ISC approaches, intercepts and completely traverses that volume. Simulation of the complex displacement processes is not the main goal of ARC and (most of) RTO tests.
CT tests provide quantitative, complete representation of phenomena: hydrodynamic, thermal, and chemical; an ISC front is generated and propagated along the combustion tube, while the temperatures inside the CT and at its wall are recorded, along with the properties of produced fluids. Simulation of the complex displacement phenomena (one-, two- and three-phase immiscible displacement), miscible displacement, heat transfer due to mass transfer between phases(vaporization / condensation) chemical phenomena of distillation, cracking, fuel formation and burning, etc. is the objective. Heat losses are not simulated (quasi-adiabatic operation), they are just minimized!
Comparative RTO curves for heavy and light oils show that, for very light oils, the reactivity of oil at low temperatures (up to 300 0C) is high enough to ensure the self-sustainability of the process. On the contrary, for heavy oil this is a lot lower and it is not enough such that the self-sustainability of the process can be ensured only if the oxidation takes place at high temperatures, in the range of 400-600 0C. In simpler words, self-sustainability of the process occurs when the peak temperature is up to 300 0C for light oils while for heavy oil the peak temperature have to be higher than 400 0C; in other words, the ISC can function properly in the LTO regime for light oils.
MOST IMPORTANT PILOTS
These pilots have been conducted in typical conditions, they used to have a very good instrumentation and a good evaluation was possible. All of them – except North Asphalt Ridge, which is reverse ISC – are forward ISC operations. Most unique and difficult (to obtain data) are specified here for each pilot.
Suplacu de Barcau, Romania
- 7 inverted 5-five-spot patterns (arranged in line) located up-dip on structure – operated for 7 years; leading to a line drive commercial operation
- 3 observations wells; maximum temperature recorded: 620 0C
- 17 coring wells have been drilled in the burned out zone, behind the ISC front, for post-mortem evaluation; the conformance factor (ratio between burned out thickness and total thickness of the oil layer) was found to be less than 35%
- Oxygen utilization efficiency: 90%-93%
South Belridge, Ca, USA
- Isolated pattern operated for a very long period of time.
- 5 observations wells; maximum temperature recorded: 510 0C
- 6 coring wells drilled in the burned out zone, behind the ISC front; the conformance factor was found to be in the range of 30% to 90%
- Oxygen utilization efficiency: 100%
- 4 inverted 5-five-spot patterns forming a confined pattern around the common production well
- 3 observations wells
- 3 coring wells have been drilled in the burned out zone, behind the ISC front for post-mortem evaluation; the conformance factor was found to be less than 35%???
- Oxygen utilization efficiency: 80-90%
North Tisdale, Wyoming, USA
- Application in the presence of bottom water
- 2 observations wells; maximum temperature recorded: 247 0C
- 2 coring wells have been drilled in the burned out zone; the conformance factor was less than 27%
- Oxygen utilization efficiency: 72% (O2 % = 6% in the produced gases)
North Asphalt Ridge (NAR), Utah, USA
There are two very well instrumented reverse ISC pilots: Bellamy, Montana USA and N Asphalt Ridge (NAR). The preference was given to the second one as the first one was conducted in a very shallow reservoir -depth 20m and the spacing between wells was extremely low – 5m. In the NAR pilot, the reservoir depth was 107 m and the spacing between well rows was 20m. After ignition, the whole NAR pilot lasted 180 days, being intentionally converted from reverse to forward ISC after approx. 90 days, when the advancing reverse ISC front reached the injection wells; therefore there was a half-half period of reverse and forward ISC.
- 13 observations wells; maximum temperature recorded: 150 0C to 400 0C for the reverse ISC phase and 540 0C to 1,100 0C for forward ISC phase
- 7 coring wells drilled in the burned out zone; the conformance factor was in the range of 30% to 90%
- Some results; average upgrading 6 degrees API and extremely high air-oil ratio ( 25,000 sm3/m3)
In the last 6 decades of ISC application there have been more than 20 large–scale ISC operations worldwide, operated for a long period of time and containing a large number of wells. The most important ones are presented here.
Suplacu de Barcau, Romania
- Shallowest ISC operation; depth of reservoir in the range of 35m to 250m
- Commercial dry ISC operation with a very low well spacing is being used, less the 2.5 acre/patterns: low pressure process (injection pressure less than 200 psi). The process displays the longest ISC front (5.3 miles), associated with the line drive operation, having 150 injection wells at the peak.
- Oil production approx. 1,500 m3/day
- Air-oil ratio (AOR) approx. 2,500 sm3/m3
Operational difficulty: mud volcanoes at surface in the area with lowest depth (35m)
Balol and Santhal, India
- Highest-pressure wet ISC operation in a heavy oil reservoir containing some coal laminations; depth of reservoir approx. 1,000m; strong lateral water drive
- Line drive operation
- Oil production approx. 1,500 m3/day from 2 commercial operations
- Air-Oil Ratio (AOR) approx. 1,000 sm3/m3
Bellevue, Lu, USA
Typical dry and wet ISC, applied in small patterns (1ha / 2.5 acres). Low pressure process (injection pressure less than 1724 kPa/250 psi). Getty Oil Co used to have the biggest exploitation, then small companies – such as Bayou Oil State Co. - continued exploitation on other areas.
Midway Sunset, Ca, USA
The non-selective oil production by ISC of a multilayer formation comprising 6 layers; initiation of ISC by spontaneous ignition.
South Belridge, Ca, USA
Both ISC and steam drive applied commercially on this reservoir. ISC applied in an isolated pattern; burned area three times larger than pattern area.
The deepest ISC process (3,447m / 11,300 ft). All three injectors were located up-dip.
Buffalo, N Dakota
The first ISC commercial application in a high-temperature, carbonate reservoir with very low permeability, containing a very light oil; the process was initiated at a very low current oil recovery.
1) ISC application for exploitation of oil sands
At the field piloting stage in Athabasca, Canada using the Toe-To-Heel Air Injection (THAI) process; the pilot started in 2006 (Whitesands project) and was completed in 2011. Most of the results are confidential.
2) ISC application for re-pressurization of gas-over bitumen reservoirs in order to facilitate exploitation of oil sands (located underneath) via Steam Assisted Gravity Drainage (SAGD)
At the field piloting stage (EnCAID test). This test was started in 2006 in Kirby Wabiskaw K-3 Pool, close to Christina Lake SAGD Project in Athabasca region, Canada. Some of the details of the pilot are confidential.
3) ISC in reservoirs with extensive bottom water
Not feasible at the current stage of development of ISC process.
4) ISC in reservoirs with extensive fractures
Not feasible at the current stage of development of ISC.
5) Self-sustaining Treatment for Active Remediations (STAR) Technology
STAR is a relatively new technology to remediate Non-Aqueous Phase Liquids (NAPLs), including coal tar and hydrocarbons from the soils/aquifers. It uses ISC to burn these hazardous liquid contaminants.
The STAR process resulted from collaboration between the University of Edinburgh, the University of Western Ontario, the University of Strathclyde, and SiREM.
Patent: Gerhard, J.I. and Torero, J. L ; 2005, STAR In-Situ Subsurface Remediation Technology, UK Patent Office, GB 0525193.9, filed 10/12/2005.
6) Underground coal gasification (UCG)
UCG makes use of the reverse ISC.
Note: So far, only UCG is a proven technology; it has been commercially applied (using a line drive configuration) in former Soviet Union.
Skafa P.V. Underground Coal Gasification. Gostoptehizdat Nauko-Tehnicescoe Izdatelstvo po Gornomu Delo, Moskow, 1960 (book written in Russian)
Davis, B.E. and Jennings J.W. : “State-of-the-Art Summary for Underground Coal Gasification” In Journ of Petr Techn, January 1984