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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
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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.
End_Page 23---------------
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
.
End_of_Record - Last_Page 25---------------