Page 169 - Fundamentals of Enhanced Oil and Gas Recovery

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Thermal Recovery Processes

displacement (SDOD) process is Toe-to-Heel Air Injection (THAITM) which is
stable in gravity. The priority of SDOD process is that it occurs ahead of ISC front.
The simulation results and laboratory scale tests revealed that this may occur as a result
of blockage near the wellbore area of horizontal wells. This leads to avoiding oxygen
short-circuiting in this process.

5.2.4.1 Benefits of THAI Process
• In this process, the front propagation is more under control in comparison to ISC
in which the breakthrough occurs at the toe and the advancement happens at the
heel.
• As in ISC process, some lab tests are required for this process.
• There are more choices available to optimize the process.
• If there is an initial mobility for the heavy oil, the process is run simpler; other-
wise, heating of the reservoir may be inevitable.
• This process is run easily at horizontal wells which are near the oil bottom layer.
• The sensitivity of this process to formation heterogeneity is low.

5.2.4.2 Criteria for THAI Application
It is important for the selected reservoirs to have the following specifications:
• If there exists a bottom water zone, its thickness should not be more than 30% of
the oil zone thickness.
• There should not exist a natural or hydraulic fracturing.
• There should be a sandstone or sand formation.
• Pay zone thickness must be more than 6 m.
3
• The oil viscosity and density should be more than 200 mPa s and 900 kg/m ,
respectively.
• The horizontal and vertical permeability of the reservoir should be more than 200
and 50 mD, respectively, and the value of K V /K H . 0.25.
• Water cut should be less than 70%.
If the reservoir permeability is increased moving to downhole, the last two condi-
tions may not be important. The final decision on starting this process is achieved by
analyzing the reservoir simulation outputs.

5.2.5 THAI With Catalyst (THAI CAPRI)
The THAI process was developed using a catalyst to increase the recovery of the
crude oil. This process calling Toe-to-Heel Air Injection (THAI)-Catalytic
Peteroleum Recovery Institute (CAPRI) was first introduced in 1998. Actually, this
process is combination of the previously described, ISC, production from a horizontal
well and catalytic cracking processes that leads to a light product with no requirement