Thermal Recovery (aka Thermal Injection) is a process of injecting heat into the reservoir to reduce oil viscosity, or thin it, and significantly enhance its ability to flow through the reservoir. It also reduces tension between rocks and liquids, which in turn improves oil mobility and result in easier flow. In addition, heated oil vaporizes, thus forming thinner oil via condensing. Thermal Recovery is the most widely used method worldwide for heavy oil projects and account for more than 60% of the global EOR production.
There are several variations of thermal recovery, such as:
- Cyclic steam injection also known as the Huff & Puff method, steam is injected into a well and then left in the well for a period of time, to heat the oil and make it flow more easily. The recovery rate of this method is less efficient than others and can only extract around 20% of the oil in place. It is a common practice to produce in cyclic steams for a few cycles and then use steamflooding method. Each cycle, inject-soak-produce can last between few weeks to months.
- Steamflood or Steam Drive is the process of constant injection of steam to the reservoir through an injection well, to heat heavy oil and improve its viscosity. In addition, as steam condenses into hot water, the additional water drive pushes the oil toward producing wells. This technique results in recovery rate of 25%-70% of the oil in place. Normally, steam is generated by using natural gas to heat the water.
- Steam-assisted gravity drainage (SAGD) is a steam injection in a more advanced approach, whereby two stacked (one above the other) horizontal wells are drilled in the reservoir, approximately 5 meters apart from each other. Pressurized steam injected into the upper well to heat the oil and make it more viscous, thus forcing heavy oil to drain into the lower well, from where it is produced to the surface. This method is mostly used in very heavy oil fields or oil sands. This technique results in recovery rate of around 50 % of the oil in place.
- Fireflood or in-situ combustion used primarily in oilfields with high saturation and porosity, this method of thermal recovery generates heat inside the reservoir. In shallow depth formations, gas burners are used to provide fire burns in the formation. In deeper reservoirs, fire burns are generated by injecting air or other gas mixture with a very high concentration of oxygen. Fire reduces the viscosity of oil by the hot gases produced by the fire flames, pushing the heated oil to producing wells. Hence, the fireflooding produces two effects: 1) thinning oil and 2) a force to move oil. Sometimes water can be injected as well, which then becomes steam inside the reservoir, creating additional force to move the oil. Combustion can be achieved by three various methods: 1) Dry forward, 2) Wet and 3) Reverse Combustion. In Dry Forward combustion fire moves in the same direction as the injected air - towards a producing well. During Wet Combustion, water is injected behind the fire burn and then transferred into steam by the hot rocks that were heated by the fire front. This method is also known as COFCAW a combination of forward combustion and waterflooding. In Reverse Combustion, fire front moves in an opposite direction to the air injected. Fireflooding or in-situ combustion technique results in recovery rate of 30%-40% of the oil in place.
In all the methods, thermal energy is generated at the surface. Source of water and power is critical. Footprint, design, complexity and costs of surface facilities and down-hole systems are dependent on the method utilized. Fields where steamflooding is used, produced water requires recovery and separation, so it can be used as feed water for boilers. Natural gas is required to heat the water and generate steam. However, today, solar energy could be used to heat water to serve the same purpose. It is has been in use successfully for many years now in Oman. The decision of power generation is driven by many factors such as availability of natural gas, weather patterns (number of sunny days) and costs.
Although steam injection and fireflooding are the most commonly used, selection of particular technique is driven by the depth of the reservoir, formation thermal properties and fluid (crude) properties. Hence, one of the key decisions to be made during any thermal recovery project planning is understanding how fast the additional drive can be transferred to the reservoir at the most cost effective way.
Supply & Demand Dynamics
Global demand of thermal recovery services is comparatively significant and the most commonly method used worldwide for heavy oil projects, accounting for more than 60% of the global EOR production. Due to relatively low costs involved, this method is the preferred methods for heavy oil EOR. Thermal recovery, as part of EOR option, will continue to dominate the EOR production for many years to come. Traditionally, thermal recovery EOR has been used extensively in North America, Indonesia and Venezuela with smaller applications in Oman, Brazil and China.
In the GCC, heavy crude fields in Oman, Kuwait, Iraq and Bahrain and their current recovery rate will create the demand. Solar EOR is expected to boost t lead the further developments in this domain.
Cost & Price Analysis
EOR production is considered as a project in itself and requires a large number of equipment and packages. Studies, pilot projects, engineering design, equipment procurement, feedstock planning, drilling and other materials, play important role in EOR projects. Upfront capital costs in EOR projects are significant.
Cost wise, thermal recovery services are composed on a number of various components, such as feed gas or solar energy, water, boiling and separation equipment, injection and close-loop cycle infrastructure.