Miscible and Immiscible Gas Injection for Enhancing of Condensate Recovery in Fractured Gas Condensate Reservoirs
- Amir Taheri (Norwegian University of Science & Tech) | Lars Hoier (Statoil ASA) | Ole Torsaeter (Norwegian University of Science & Tech)
- Document ID
- Society of Petroleum Engineers
- EAGE Annual Conference & Exhibition incorporating SPE Europec, 10-13 June, London, UK
- Publication Date
- Document Type
- Conference Paper
- Society of Petroleum Engineers
- 5.8.6 Naturally Fractured Reservoir, 4.1.2 Separation and Treating, 4.6 Natural Gas, 5.2 Reservoir Fluid Dynamics, 2.2.2 Perforating, 5.2.2 Fluid Modeling, Equations of State, 4.1.5 Processing Equipment, 5.5 Reservoir Simulation, 1.2.2 Geomechanics, 5.2.1 Phase Behavior and PVT Measurements, 5.4.2 Gas Injection Methods, 5.8.8 Gas-condensate reservoirs, 4.1.9 Tanks and storage systems
- fracture, immiscibility, miscibility, condensate
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Gas condensate reservoirs usually exhibit complex flow behaviors because of accumulation of condensate in the reservoir and two-phase flow of gas and condensate when the reservoir pressure drops below the dew-point. In some complicated geological systems like naturally fractured reservoirs, these complex behaviors will be more. In these systems, pressure drop response propagates in the fracture network and all the matrix blocks surrounded by fractures are influenced by pressure drop in the wellbore. This causes accumulation of large amount of condensate in the matrix blocks entire the reservoir when the pressure drops below the dew point. Usually, the accumulated condensate saturation in the matrix blocks of fractured reservoirs is lower than the critical condensate saturation that causes trapping of large amount of condensate in the matrix blocks. So selection of an efficient EOR scenario for recovering this trapped condensate is important.
In this paper, a single matrix block surrounded by fractures is used to study the performance of a fractured gas condensate system in natural depletion, miscible and immiscible gas injection. C1, N2, CO2 and stock-tank gas composition are considered as injection gases and their miscibility with condensate is studied. Also some sensitivity analyses were performed on different parameters for more accurate investigation about the effects of different parameters on performance of the fractured system in different production scenarios.
In both miscible and immiscible gas injection scenarios, the timing for injection and injection gas composition are two key parameters. In miscible gas injection case, miscibility is the main mechanism for condensate production, while in the case of immiscible gas injection scenario, vaporization of condensate by injected gas is the more efficient mechanism for condensate recovery. Gas-gas miscibility mechanism is more efficient in comparison to gas-condensate miscibility in miscible gas injection and vaporization in immiscible gas injection scenario.
Complexity of gas condensate systems is mainly due to the complication of gas condensate fluids. Considering complicated porous media like fractured systems, the analysis will be difficult and simulation of these types of reservoirs from geomechanical and thermodynamical point of view is faced with many problems.
In fractured gas condensate reservoir, by production and dropping the pressure below the dew point, condensate is formed in the matrix and fracture. There are few publications about condensate recovery mechanisms in fractured gas condensate reservoirs. Gravity drainage, molecular diffusion, viscous and capillary forces and compressibility are the production mechanisms that must be considered in production and enhancing recovery from fractured gas condensate reservoirs.
One of the most important mechanisms of condensate recovery from fractured reservoirs is gravity drainage. Castelijns and Hagoort in 1984 studied condensate recovery due to gravity drainage in Waterton reservoir in Alberta which has a large fracture network. Because of pressure drop in fractures, condensate is first formed in the fractures. This condensate has the capability of entering into the matrix block near the fracture due to imbibition process. This capability is opposed by viscous force of the expanded gas in the matrix and finally when the rate of imbibition is less than the rate of condensate deposition, some part of deposited condensate moves downward and collects in the downstream of the reservoir. Since the fracture pore volume is too small, very small amount of condensate is formed in the fracture that quickly imbibes into the matrix. Instead, the amount of condensate that is formed in the matrix and drains into the fracture can be considerable (Castelijns and Hagoort 1984).
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