Toe-To-Heel Waterflooding. Part ll: 3D Laboratory-Test Results
- Alexandru T. Turta (Alberta Research Council) | Ashok K. Singhal (Alberta Research Council) | Jon Goldman (Alberta Research Council) | Litong Zhao (Petro-Canada)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 2006
- Document Type
- Journal Paper
- 202 - 208
- 2006. Society of Petroleum Engineers
- 6.5.2 Water use, produced water discharge and disposal, 5.2.1 Phase Behavior and PVT Measurements, 5.4.1 Waterflooding, 4.3.4 Scale, 5.4.2 Gas Injection Methods, 5.3.9 Steam Assisted Gravity Drainage, 2.2.2 Perforating, 4.2 Pipelines, Flowlines and Risers, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.1.1 Exploration, Development, Structural Geology, 5.4 Enhanced Recovery, 4.6 Natural Gas, 1.6 Drilling Operations, 5.4.6 Thermal Methods, 5.7.2 Recovery Factors
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A new waterflooding process, toe-to-heel waterflooding (TTHW), was developed, based partly on a recently developed thermal TTH displacement process, TTH air injection (THAI). TTHW is a novel oil-recovery process that uses a horizontal producer (HP) and a vertical injector (VI). The HP has its horizontal leg located at the top of formation, while its toe is close to the VI, which is perforated at the lower part of the formation.
TTHW realizes a gravity-stable displacement, in which the water/oil mobility ratio becomes less important and its detrimental effect on sweep efficiency is diminished; the injected water always breaks through at the toe, after which water cut gradually increases.
A systematic investigation of the TTHW process in a Hele-Shaw laboratory model mimicking a simulated porous medium showed that the process substantially improved the vertical sweep efficiency as compared to conventional waterflooding. Following these semiquantitative tests, a more comprehensive 3D-model testing was undertaken to investigate the overall sweep efficiency of the process. The 3D model consists of a metal box filled with glass beads and saturated with oil at connate-water saturation. Oil was displaced with high-salinity brine, either in a TTH configuration or in a conventional array, using only vertical wells.
A staggered line drive was used by injecting water in two vertical wells located at one side of the box and producing oil by using either an HP with its toe close to the injection line or a vertical producer located at the HP's heel position.
Several TTHW tests were carried out at different injection rates. For a given injection rate, the TTHW results were compared to those of conventional-waterflooding tests. For the same amount of water injected, the ultimate oil recovery increased by a factor of up to 2, as compared to that for conventional waterflooding.
All in all, the results of these investigations show that the novel TTHW process is sound and can be optimized further.
Conventional waterfloods in heavy-gravity-oil reservoirs (oil viscosity higher than 100 mPa.s) are limited by three main factors:
• Reservoir heterogeneity, leading to water channelling.
• Gravity segregation (caused by oil/water density contrast), leading to underriding of the injected water.
• Highly unfavorable water/oil mobility ratio, which aggravates the adverse effects of the first two factors.
Usually, the heterogeneity is caused by pronounced vertical stratification, manifested by a relatively large contrast in the horizontal permeability of different layers. On the other hand, the negative effect of gravity segregation is felt mainly when the stratification is not very pronounced and effective vertical permeability of the pay zone is relatively high.
The effect of gravity segregation on waterflood performance was reported in 1953 when the first mathematical model of water tonguing (underriding) was published by Dietz (1953). Initially, Dietz's theory was believed to be applicable mostly to thick formations. However, subsequently, Outmans showed that this theory was equally applicable to thin oil formations (Sandrea and Nielsen 1974).
|File Size||1 MB||Number of Pages||7|
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