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Transcript of SPE-116528-MS
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SPE 116528
Horizontal Well Best Practices to Reverse Production Decline in MatureFields in South China SeaYou Hongqing, Wei Ping, Tian Xiang, Xu Xiang Dong, Lian JiHong, Thanh Tran, Yoseph J. Partono : CACT,Jeffrey Kok, Liu Yang, Sarfraz Balka: Schlumberger
Copyright 2008, Society of Petroleum Engineers
This paper was prepared for presentation at the 2008 SPE Asia Pacific Oil & Gas Conference and Exhibition held in Perth, Australia, 2022 October 2008.
This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not beenreviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, itsofficers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission toreproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.
AbstractThe Huizhou 6S and 3S oil fields in the Pearl River Basin,
Offshore South China Sea are mature fields which have
produced 40% to 60% of their original oil in place since1991. Currently the field production is rapidly declining
and water production is increasing. However, through
reservoir surveillance data, geologic and reservoirmodeling, significant recoverable oil was identified in
shaly sandstone reservoirs and attic structural locations of
clean sandstone reservoirs. As a result, a comprehensiveportfolio of prospects has been built for a robust
development program. Horizontal wells were utilized toimprove oil recovery in shaly sands and to reduce water
coning in thin remaining oil columns. Horizontal drillingbest practices were applied during well planning and
drilling executions, such as optimum well designs,specific LWD/MWD tool selections, low fluid loss
drilling fluids, real-time geosteering data monitoring and
the cleaning of the pay zone during completions were
applied to maximize reserve recovery and successfullyreverse the fields production decline.
IntroductionThe Huizhou Oil Fields are located in the Pearl River
Mouth Basin, South China Sea approximately 190 kmsoutheast of Hong Kong (Figures 1). Agip, Chevron and
Texaco signed the contract in 1983 and they discovered
nine prolific oil fields by the year of 1989. Firstproduction in this area was from the Huizhou 1S field in
1990 followed by Huizou 6S field in 1991 and Huizhou
3S field in 1995. There are currently 7 platforms and anFPSO which are producing oil and gas from 10 fields.
New efforts were put in the exploration activity with the
drilling of exploration and appraisal wells in the period of2002-5resulting in another significant discovery and the
commercialization of two previously discovered fields.
Geological OverviewHuizhou 6S and 3S oil fields are located in Pearl River
Mouth basin, South China Sea, which is a continental
margin sedimentary basin formed during the rifting of theSouth China Sea in the Late Mesozoic to early Tertiary.
The main pay zones where CACT deploys horizontal and
multilateral well technology were deposited as delta frontbar and coalesced, stacked fluvial-deltaic channel sands in
early Miocene time. Oil accumulations with low gas
saturation and no gas cap are mostly found in 4-way-dipclosures, which are associated with basement highs. In
some cases the traps are also associated with sand layerpinch-outs.
The reasons for drilling horizontal wells arepredominantly based on the following two considerations:
Firstly, after over 15 years of high rate oil production,these fields have gradually entered into a mature and
high-water-cut phase. Oil to water contacts (OWCs) have
significantly encroached upward leaving thin remaining
oil columns and causing high water production from all ofthe existing wells. Due to reservoir heterogeneity, some
of the reservoirs exhibit uneven strength of aquifersupport causing OWCs to tilt after years of production.
To reduce and reverse the rapidly declining oil production
rate is a challenge CACT needs to confront. Tosignificantly improve production efficiency of theremaining potential attic oil locations, horizontal well is
the first priority among various alternatives.In addition, the poor petrophysical properties of shaly
layers did not effectively produce oil from vertical wells.
The recent horizontal and multilateral wells in these shaly
zones have greatly improved production performance andfield recovery. The petrophysics and depositional
environment of the reservoirs are briefly described asfollows.
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in vertical depth which could be detrimental to
the success of a horizontal well drilling and
completion. This risk may be mitigated bydrilling a pilot hole prior to drilling the
horizontal well. In May 2008, CACTreprocessed the 3-D seismic data using a pre-
stacked depth migration (PSDM) technique to
reduce the structural risk.- The risk of not finding sufficient oil
accumulation because the current OWC have
moved higher than expected leaving too thin oilcolumn to produce. If there is no recent
information on the current fluid contact within
the radii of 1000m, it is important to acquire data
to locate the current OWC. Cased hole loggingin nearby wells is a low cost option to survey the
current fluid contact. If reliable cased-hole datacannot be acquired, a pilot hole is to be drilled
prior to drilling a horizontal well.
To anticipate the possibility that the pilot hole does notproof sufficient reserves in the target reservoir due to the
above risks a backup target (Figure 5) is prepared as acontingency against drilling an uneconomic horizontal
well.
Pre-drilling PreparationOnce a horizontal target is selected a detailed well course
is planned to ensure successful placement of thehorizontal section in the reservoir, casing run, casing
cementation and installation of completion.
1. Optimum Well Plan
The design of the well plan requires close collaboration
between geologist and drilling engineer in order to ensurethat the well trajectory is drillable and to reduce risks tothe lowest level and to achieve the best performing well.
The direction of the existing well to be sidetracked does
not usually following the simplest route to reach the targetlocation because of proximity with other existing wells.
This condition causes difficulty in achieving low well
tortuosity and dogleg severity, where iterative targetadjustments are required to optimize the well plan and
ensure the modeled torque and drag are within allowable
limits.A tangent section of 5m true vertical depth (TVD) above
the target is generally planned to accommodate
uncertainties in the geologic structure interpretation anddirectional survey. (Fig 6)
Landing point of the horizontal section is typically
planned 1m or less below the top of the reservoir to allowmaximum displacement from the current OWC. The
angle along the horizontal section should not exceed 90
degrees to avoid a goose-neck trajectory that could
cause water blockage during production. Depending onthe quality of the reservoir and the simulation results a
horizontal section of 300 to 1000m are planned.To accommodate difficult well drilling operations the
following upgrades were done on the platform and
drilling equipment:
1- 225 tons pipe deck and 3500 m new derrick
2- Hoisting rating: 350 klbs3- Hydraulic TDS: 37,000 ft-lb
4- Mud pumps: 2 x P-750 + 1 x 3NB-800
5- Mud tank: 900 bbls including one removabletank
6- Shale Shakers: 3 X Derrick Hydrill2000 with
0.47 cubic feet per min for each7- Centrifuge: 1 X Swaco518FVS
Well Profil e
All the well profiles were designed in 3-D, (Fig 7). In
order to conventionally hit the planned target TVD,
medium to high doglegs from 3.5 to 4.5 are required.
But it was possible to limit doglegs to the minimum bydropping the inclination with a turn first and then building
in the other direction. While designing the well profile, atangent section for ESP and holding of inclination from
85-87 for a soft landing were also key requirements.
The average open hole length for the sidetrack wellvaries
between 2000 to 2500m. The 3-D profile designs producehigh tortuosity and high Directional Difficulty Index (Fig
8 and Fig 9), where the average tortuosity can varybetween 220-250. Using a water base mud system
further increased the torque and drag issues. To over-
come this, basic drilling surface parameters such as RPM,
WOB, mud pump flow rates are controlled. In addition,well bore improvement techniques such as adding
lubricants to lower friction factors and the usage of rotarysteerable system (RSS) were employed. The application
of RSS tool delivered excellent drilling results in all the
wells, with the exception of one case where the tortuosity
increases above 250 deg that created some issues whenrunning a 7 liner.
Depending on the reservoir properties, multilateral wellswere also planned. The side track point selection was akey element of success that required detail planning and
execution by the drilling and reservoir teams. In total,
three multilateral wells were successfully drilled andcompleted with the combined teamwork and proper BHA
selection.
2. Technology Selection
Whipstock and mi lli ng Window: In many occasions there
is little cement behind the casing where a sidetrackwindow is milled. This leaves a sharp, off-sized window
that causes problems when a drilling BHA or casing
packer is passed through. As a remedy, a cement squeezearound the window is performed, giving very positive
results. Experiences from other parts of the world showed
that after the milling operation, the drilling BHAs had thetendency to track the casing. To address this problem, the
whipstock on CACT wells are set either left or right of the
high side.
Bi t Selection: Historically in CACT, drilling with water
base mud (WBM) in abrasive formation with the presenceof hard and interbedded stringers greatly reduces a PDC
bits performance with bit balling and premature broken
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hole and modeling the liner run with various simulations
to determine the number and position of liner centralizers
required.With this practice, all the wells except one underwent
very good results with the liner run arriving to bottom. Inthat single case (well HZ6S-10Sb), the liner got
prematurely stuck leaving almost 400m of open hole
exposed. Further investigations identified the root causeof such sticking to the liner hanger assembly. As aremedial, a rotating liner hanger was implemented for
future liner designs to help break down the excessivefriction by liner rotation and push the liner to bottom.
ConclusionsHorizontal and multilateral wells have proven effective to
produce remaining oil in thin columns and shaly
formations in mature HZ3S and HZ6S oil fields.
Current surveillance data and pilot holes are essentials toprovide controls for drilling horizontal wells.
Vigilant team work between subsurface, well placement
and drilling teams during all phases of operations,including reservoir modeling, well planning and well
drilling was necessary to provide strategic planning with
contingencies for the best and timely real time decisions.The sidetrack campaign on the HZ3S and HZ6S fieldsin
2007 successfully reversed the production decline wherethe cumulative oil in 2007 from four sidetrack wells
totaled around 1.5MMSTB. This accounted for 30% of
the total field production where the oil rates from these
four wells held 30% of the total field production.
AcknowledgmentsThe authors would like to thank CACT, CNOOC, ENIand Chevron for the permission to publish this
information.
AbbreviationLWD: Logging while drilling
MWD: Measurement while drillingFPSO: Floating Production Storage & Offloading
OWC: Oil Water Contact
BOPD: Barrels of Oil per Day
PVT: Pressure-Volume-TemperaturePSDM: Pre-Stacked Depth Migration
TVD: True Vertical DepthTDS: Top Drive System
ESP: Electric Submersible Pump
RPM: Revolutions per MinuteWOB: Weight on BitRSS: Rotary Steerable System
PDM: Positive displacement mud motor
BHA: Bottom Hole AssemblyPOB: Personnel On Board (Rig or Platform)
WBM: Water Based Mud
PDC: Polycrystalline Diamond CompactROP: Rate of Penetration
DIF: Drill in Fluid
API: American Petroleum InstituteTD: True Depth
RT: Real Time
RTGS: Real Time Geosteering Software
DLS: Dogleg Severity
CD&I: Continuous direction & inclinationMMSTB: Million Standard Barrels "oil"
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Figure 1: CACT oilfields location map
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Figure 2: Generalized stratigraphy of Pearl River Mouth Basin.
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Figure 5 Cross section showing a planned horizontal well with a pilot hole and a backup horizontal target
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Fig 6: Depth Uncertainties in Landing a Horizontal Well
Fig 7 Well Profile
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Fig 8 Torque and drag modeling, Tripping load analysis will be required
Fig 9 Torque and drag modeling, Tripping load analysis will be required
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ADN475 RT Image on InterAct
Layer 1entr
Cutting up strat
Fig11 Density Image Example
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Fig 12 Landing Model and Correlation Example
Fig 13 Horizontal Section