Application of Thermal Recovery and Waterflood to Heavy and Extra-heavy Oil Reservoirs: Analog Knowledge from More Than 120 Clastic Reservoirs
- XiaoGuang Lu (C & C Technologies, Inc.) | Shaoqing Sun | John Xu
- Document ID
- Society of Petroleum Engineers
- International Oil and Gas Conference and Exhibition in China, 8-10 June, Beijing, China
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
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- 1,116 since 2007
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More than 120 clastic reservoirs were examined to extract knowledge of application of thermal recovery and waterflood to heavy or extra-heavy oil (less than or equal to 25 ºAPI gravity). The thermal recovery methods discussed include cyclic steam injection, steam flood, in-situ combustion, hot water injection and SAGD. Key parameters of reservoir and fluid properties and production engineering are summarized in detail for reservoirs where one or more of the above EOR methods or waterflood are applied. These include: (1) reservoir characteristics such as sandbody facies type, permeability, porosity, oil saturation, reservoir depth, net pay
thickness and net to gross ratio; (2) crude oil properties including API gravity, viscosity, GOR, and FVF; (3) well spacing and ultimate recovery factor; and (4) controls on incremental recovery and ultimate recovery factor.
Controls on ultimate recovery factor for each of the above methods were analyzed. It was found that the basic controls are API gravity, viscosity, reservoir depth, net to gross ratio and well spacing. Thermal recovery methods are mainly applied to reservoirs less than 1100 m deep with crude oil API gravity less than 20º, and typical well spacing of 2-5 ac. The ultimate recovery factor is variable, ranging from 9% to 79%. The most commonly applied thermal recovery methods are cyclic steam injection and steam flood. In-situ combustion has also been successfully applied to some reservoirs with ultimate recovery up to 45%. SAGD technique applied to extra-heavy oil reservoirs is able to improve recovery by 45% to 50% of STOIIP.
Waterflood, which has been widely applied to relatively "light?? heavy oil with API gravity greater than 15º, can yield good recovery provided that well spacing is close and throughout injection is sufficient. The secondary recovery method is usually implemented in reservoirs at depths greater than 600 m with well spacing of 6-50 ac. Typical ultimate recovery factors for reservoirs with waterflood ranges from 20% to 45%.
Thermal recovery, as the key EOR method for heavy and extra-heavy oil, consists mainly of cyclic steam injection, steam flood, in-situ combustion, and hot water injection. SAGD technique, developed in the late 1970s, for thick and high permeability reservoirs with extra-heavy oil has also been commercialized successfully (Albahlani and Babadagli, 2008). It has been considered the standard technique in extra-heavy oil reservoir. Thermal recovery processes are the most advanced EOR methods and have contributed significant amount of oil production. Most thermally recovered oil is from cyclic steam injection and steam flood (Green and Willhite, 1998).
In the meantime, waterflood is becoming increasingly important in heavy oil production. Study using data from around the world shows that heavy oil (API gravity 13 to 25º) reservoirs are routinely water flooded with excellent recovery. Conclusions were drawn that simple water flood operations for viscous oil should be the base process for improved oil recovery, and recovery of viscous oil via waterflood will improve with reduced well spacing and larger volumes of injection water (Beliveau, 2008). Further study focusing on increasing recovery from heavy oil waterflood suggests that certain amount of pre-waterflood production and certain amount of pre-injection time are beneficial for ultimate waterflood recovery (Brice and Renouf, 2008).
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