|The THAI process. Not to scale. Click to enlarge.|
Petrobank, a Calgary, Canada-based oil and natural gas exploration and production company, is commissioning its WHITESANDS oil-sands pilot project using the proprietary in-situ THAI combustion process. Pre-ignition warming is scheduled to begin in February, with combustion initiating by May 2006.
The THAI (Toe-to-Heel Air Injection) process combines a vertical air injection well with a horizontal production well.
During the process a combustion front is created where part of the oil in the reservoir is burned, generating heat, thereby reducing the viscosity of the remaining oil. Gravity pulls the oil to the horizontal production well.
The combustion front sweeps the oil from the toe of the horizontal production well (the underground termination of the horizontal portion) to its heel (the transition of the production well from horizontal to vertical).
THAI promises recovery of an estimated 80% of the original-oil-in-place while partially upgrading the crude oil in-situ. Petrobank also holds the rights to a well-bore integrated catalyst (CAPRI), the use of which could further upgrade the syncrude in-situ.
|3D rendering of project site, with aerial surface photo of project site inset.|
WHITESANDS is a C$30-million (US$26-million) pilot project that consists of three horizontal wells (500 metres long and 100 metres apart), three vertical air injection wells and 19 vertical observation wells (17 for temperature and two for pressure observations).
Peak production from the three wells is estimated at 1,800 barrels per day or 600 barrels of oil per day per horizontal well (1.8 kbpd total).
Pre-ignition warming consists of heating the oil sands formation—which is about 370 meters (1,200 feet) below the surface— by injecting steam through the air injection and production wells for a period of two to three months.
After the pre-heating period, air is then injected into the oil sands through the air injection wells. As the air reaches the heated oil sands, combustion begins. A 2m-thick vertical combustion front will form that will move forward along the horizontal well at about 25 cm (10 inches) per day.
Combustion here refers to the flameless, high-temperature oxidation of the heavier part of the bitumen (called coke) left behind as the process proceeds.
Hot combustion gases that are depleted of oxygen contact the oil ahead of the combustion zone and heat the oil to above 400ºC. The high temperatures in the presence of formation clays cause thermal cracking and upgrading of the oil by 7–8º degrees API gravity in laboratory physical models.
The hot, lighter cracked oil, reservoir water and combustion gases (primarily nitrogen and carbon dioxide) drain downward into the horizontal well for transmission directly to the surface for processing by produced gas lift.
Some virgin oil warmed by conductive heating ahead of and behind the combustion front also drains into the horizontal well. Up to ten percent of the original oil, the heavier, higher-boiling fraction, is left behind on the rock formation and becomes the combustion fuel as the burning front advances. THAI consumes only air as an injected raw material.
A water supply well will provide the water source for WHITESANDS. A second well may be installed to serve as a backup, and for monitoring water levels and the chemical quality of the groundwater. Petrobank estimates maximum groundwater production rates for Year 1 and Years 2 to 5 are currently estimated to be approximately 725 m3/day and 575 m3/day, respectively.
Assuming full 1,800 bpd production (286 m3) and the lower water rate for years 2 through 5, that works out to a project water-to-oil ratio of 2:1. In other words, two barrels of project water for every barrel of oil.
WHITESANDS will also generate a number of waste streams requiring disposal. CO2 emissions will be a projected 30,600 m3 per day (based on a 12% component of daily produced gas waste of 255,000 m3).
|WHITESANDS Project Waste Streams|
|Waste Stream||Flow rate||Storage/Disposal||Characterization|
|Sand||Net solids: 1 m3/day||Enclosed tank with vapor recovery. Trucked out.||Sand with a hydrocarbon residue.|
|Water softener||7 m3/day||Disposal well||High mineralized water. (During startup only.)|
|Steam generator blowdown water||20 m3/day||Disposal well||Highly mineralized water. (During startup only.)|
|Tank blanket gas||400 m3/day (dry)||Flared (incinerated)||Methane, CO2 with an H2S component.|
|Combustion gas||255,000 m3/day||Vented to atmosphere||Nitrogen (82%), CO2 (12%), with sulfur components.|
|Produced water||120 m3/day||Disposal well||Water created by THAI process and produced water.|
According to Petrobank, THAI offers a number of potential benefits over other in-situ recovery methods, such as SAGD (Steam Assisted Gravity Drainage), including higher resource recovery; lower production and capital costs; reduced usage of natural gas and fresh water; a partially-upgraded crude oil product; reduced diluent requirements for transportation; and lower greenhouse gas emissions.
Petrobank will begin the pre-ignition-warming-cycle on the first horizontal production/vertical air injection well pair in early February. All three well pairs are expected to be on production by the end of 2006.