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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: An Integrated Study of the Liuhua
11 - 1 Field Using an Ultra-High
Resolution
3D Seismic Dataset:
South China Sea


By
1CAEX Services Inc.,
2BP Amoco
3Freze Unrversitaet Berlin
4CNOOC
Introduction
The Liuhua 11-1 field, located 130 miles southeast of Hong Kong in 1000 feet of water, is a vuggy carbonate reservoir at shallow depths (3850 feet subsea), producing 16-22 degree API oil under a very strong bottom-water drive. The field was discovered in 1987 and is currently being developed with 25 long-radius horizontal wells drilled from a floating production system. Project success is dependent on limiting water production with the heavy oil, which in turn makes an accurate reservoir description critically important.
To better define reservoir heterogeneity, a 3D seismic survey of the
Liuhua Field was acquired in July 1997. A very high resolution
dataset (200+ Hz) was obtained and has been used in an
integrated field study to evaluate the future exploitation potential
of the 1.2 billion barrels of oil in place in the reservoir.
The seismic data were converted to acoustic impedance using geologically-constrained inversion techniques and converted to porosity based on a linear impedance vs. porosity relationship. Drilling data were integrated with the seismic data to create detailed maps of reservoir structure and stratigraphy. Petrophysical data and modeling coupled with the seismic inversion were used to create a spatial distribution of porosity, permeability, and saturation. Faults, fractures, and oilfield karst collapse phenomena in the reservoir were analyzed using coherence technology. Complex attribute analyses added an additional understanding of rock matrix continuity. This information was used to build reservoir characterization and simulation models that were tuned and validated using historical performance to predict future reservoir performance.
Conclusions
Much of the prior geoscience understanding of the Liuhua reservoir
was revised significantly as a result of this work. The
structural location of the wellbore is a critical factor along with
the internal faulting, fracturing and solution
collapse, the porosity
and permeability of the flow units, and the integrity of the
tight zones. A significant finding, demonstrated by the porosity
model, is the heterogeneity and lack of continuity in the tight
layers as called for in the original pre development plan. The
Liuhua reservoir is riddled with porosity soft spots and suspected
fracture swarms in the baffle zones that were originally required
to be spatially competent as tight protection from early aquifer
influx.
Solution
collapse and gas chimneys are also critical factors
affecting reservoir hydraulics, and the associated
vertical
water movement was simulated successfully using attribute
analyses during flow modeling around the horizontal wellbores.
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Figure 1. 3D image of the top of the Liuhua reef complex Fault breaks shown as gaps; karst features as deep holes.
Figure 2. Coherence image of the reservoir top. Large circular features are karst collapse zones; linear features are faults.
End_Page 24---------------
Figure 3. Reflection strength
attribute section showing amplitude
loss in the gas chimney zones within
and above the reservoir. Vertical
water flow associated with the
oilfield karst features was modeled
in the reservoir simulation.
Figure 4. Combined structure and property model in depth showing carbonate porosity flow units input to reservoir simulation.
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