Written by X. G. Lu, S. Q. Sun, and J. Xu
Published by the Society of Petroleum Engineers
Sourced from the International Oil and Gas Conference and Exhibition in China, 8-10 June, Beijing, China, 2010
Copyright: 2010. Society of Petroleum Engineers
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 summarised 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 analysed. 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%.