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Abstract
The Cao Fei Dian (CFD) field located in Bohai Bay, China contains numerous
commercial oil fields comprising shallow
multi-layered reservoir sands in the Ming and Guantao formations. The
depositional basins containing the Ming and Guantao
sands are inter-bedded with reactive clays in the hydrocarbon-bearing
formations, with multiple pay zones being isolated by
similarly reactive shale zones. The development plans for the fields called for
predominantly horizontal openhole gravelpack
completions, requiring highly inhibitive drilling and completion fluids to
counter the reactive nature of the formations.
A secondary area of concern was the interaction between drilling fluid filtrate
and completion brines with the crude oil. A
cost-benefit analysis indicated the option for oil-based mud, the preferred
completion method and costs associated with a
zero-discharge environment, was not feasible due to the environmental
restrictions.
Prior to development of the first commercial field, extensive laboratory
studies were conducted on cuttings and crude oil
samples collected from exploration and appraisal wells. This series of tests
helped to determine the preferred drilling and
completion fluid program for the field, resulting in a highly successful Phase
1 development project for the CFD 11-1 and
CFD 11-2 fields. Prior to commencing drilling and completion operations on
offsetting fields, additional testing was
undertaken to confirm the fluids of choice were satisfactory. This second
series of tests proved surprising in that the fluids
used in Phase 1 were inappropriate for offset development projects due to
unsatisfactory shale inhibition and adverse crude
oil reactions.
A new series of tests were required to determine optimal shale inhibition
and prevention of crude oil emulsification. This
paper discusses in detail the specific tests performed to optimize production
from the fields prior to drilling, together with
specific examples of the benefits gained from the fluid testing during
execution of the drilling and completion program. To
date more than 40 post-Phase 1 development wells have been completed
successfully in the on-going development project,
including record step-out wells for Bohai Bay, together with an additional
eight exploration and appraisal wells drilled in the
exploration phase.
Introduction
In 1999 the CFD 11-1-1 exploration well was drilled, producing high flows of
oil and gas from the Guantao Formation. High
yield also was shown in the Lower Ming. After the drilling success of the CFD
11-1-1 well, two follow-up evaluation wells
were drilled: CFD 11-1-2 and CFD 11-1-3. Both evaluation wells encountered
commercial oil flow in the Upper Tertiary.
Further evaluation wells were drilled during 2000 and 2001 and seismic, well
test and log data were analyzed before
launching the Phase 1 CFD 11-1 and CFD 11-2 development campaigns.
The first development well was spudded in November 2003 and the CFD 11-1 and
11-2 development phase continued
until early 2006 with a total of 42 wells drilled and completed. These wells
primarily were drilled in interval batches. The
general well design includes a driven conductor followed by 17½-in hole section
by 13⅜-in casing, 12¼-in hole by 9⅝-in.
casing followed by a horizontal 8½-in openhole interval completed by running
premium screens and gravel packing.
In 2005 and early 2006 three new fields were planned for development: CFD
11-3/5, CFD 11-6D and 12-1E. While these
wells use approximately the same well design to penetrate the same reservoirs
encountered in CFD 11-1/2, and are
geographically close to the CFD 11-1 and 11-2 fields, significant differences
in properties of the reservoir interbedded shales
were noted as well as variations in the produced crude.
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