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Development strategies for Keshen 2 gasfield,
an ultra-deep naturally fractured tight
sandstone gas reservoir in Tarim basin
Zelong Wang, Ailin Jia
CNPC Research Institute of Petroleum Exploration & Development
Sept. 2019
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Contents
Gasfield overview
Current challenges
Development strategies
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Gasfield overview Keshen 2 gasfield located in the mountainous Kelasu structural belt in
northern Tarim Basin
Primary gas source for the West-to-east pipelines
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Surface is dominated by mountains and ravines without vegetation
Max relative relief can be 500m, max outcrops dip angle over 80°
Burial depth of 6500~7600m, covered by massive salt layers
Naturally fractured tight sandstone reservoir
Dry gas reservoir with complicated gas/water contacts
Reservoir thickness: 300~650m
Structure dip: 30~50°
Temperature: 120~193℃
Reservoir pressure: 116~128MPa
Porosity: 1.5-7%
Average permeability: <0.049mD
1. Geographic and geological characteristics
Keshen 2 reservoir profile (East-West)
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Difficulties in seismic data acquisition, processing and interpretation caused by
complex surface and severely superposed underground structure
Difficulties in drilling due to the existence of gravel layers and severely crept salt-
gypsum formations
Difficulties in reservoir stimulation due to large burial depth and tight sandstone
High risks in downhole well testing due to high formation temperature and
pressure
Difficulties in environmental protection due to the fragile ecological system of the
mountainous area
2. Difficulties in the early phase of development
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Development began in 2009, the first well produced in Oct. 2011, the
preliminary program worked out in July 2013, the field went on stream
in July 2015
Tens of wells have put into production, with high initial gas rate up to
about 900×103 m3/day
Well watering occurred in 2015, and becoming a more general problem
Due to the unexpected watering and sanding problems, current gas
rate couldn’t reach the original target
3. Gasfield development status
Gas rate Tubing pressure
A typical Keshen 2 well production profile
Gas
rat
e( ×
m3/d
ay)
Tub
ing
pre
ssu
re (
MP
a)
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Contents
Gasfield overview
Current challenges
Development strategies
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Ultra-deep HTHP reservoirs are extremely difficulty for seismic data acquisition
and interpretation
Reservoir matrix is tight sandstone, the fluid pathways are dominated by fractures,
and reservoir connectivity controls the flow streams and watering directions
Locate “sweet spots” fracture concentrated zones to obtain high productivity
Difficulties in fracture characterization and reservoir connectivity description due
to lack of implicit and high resolution data
1. Structural modeling and fracture characterization
Fracture intensity map of the top Bashijiqike formation
(1) Challenges
Well K-1Well K-2 Well K-3 Well K-4
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Structural modeling based on detailed seismic acquisition and interpretation
Wide-range, high density seismic survey and nova interpretation techniques
Fracture identification with multi-data integral interpretation
image log, core, outcrop, micro seismic, production data, drilling log, etc.
Reservoir connectivity evaluation based on static/dynamic data analysis
Sedimentary, reservoir pressure, fluid composition, well test, production data, etc.
1. Structural modeling and fracture characterization (con’t)
Fracture identification with multi-data integral interpretation
(2) Solutions
Core K1bs2,6800m,half-sealed fracture
Outcrop of Bashijiqike formation
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Complex water/gas contacts due to structural complexity and intense fractures
system
Watering severely affected well productivity and blocked gas pathways in the
reservoir
Difficulties in characterizing water distribution and generalizing watering patterns
2. Complex water/gas contacts and watering
Keshen 2 reservoir gas saturation in 2017
(1) Challenges
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Fracture identification with multi-data integral interpretation
image log, core, outcrop, micro seismic, production data, drilling log, etc.
Reservoir connectivity evaluation based on static/dynamic data analysis
Sedimentary, reservoir pressure, fluid composition, well test, production data, etc.
Watering patterns recognition and pre-warning techniques
Established 4 watering patterns/type curves, rate transient analysis , numerical
simulation, etc.
Reservoir watering patters and their typical production curves
(2) Solutions
2. Complex water/gas contacts and watering(con’t)
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Contents
Gasfield overview
Current challenges
Development strategies
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Use the best knowledge to make a development plan, revise the
plan along the field development, and optimize production
strategies over time
Closed-loop reservoir management
Sketch of closed-loop reservoir management
Geomodeling, with multi- data constraint
Dynamic data measurement
Data assimilation (history matching)
Strategies optimization
Repeat the cycle until the abandonment
14The latest reservoir models of Keshen 2
Porosity model Permeability modelFacies model
Reservoir structural modeling evolves as more data is acquired
2010,Detailed prospecting
2009,Secondary prospecting
2007,Preliminary prospecting
2013, development planning
2015, re-interpretation
2017, modification
Understanding on Keshen structural belt changes over the years
Seismic survey and interpretation, outcrops, well logs, well testing, core lab, etc.
1. Structural modeling evolution
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2. Facies and fractures modeling
+
Geological
understanding
Petrel®
facies modeling
FracaFlow®
fractures modeling
3D-DPDP
reservoir modeling
Fracture porosity Fracture permeabilit
Discretized fractures
Dynamic data modified
Fault screening
Sedimentary facies (reservoir matrix)
Objective based modeling
geological dictionary (outcrops)
Seismic impedance
(interlayer thickness probability)
Multi-data constraint fracture modeling
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3. Dynamic data monitoring and interpretation
Sanding and watering damaged the well deliverability
Sanding wells productivity decreased 85%, watering wells decreased 76%
Sanding wells analysis
Sanding particles: reservoir sands, proppants, cements, iron fillings
Regulate production rate: critical sanding flow rate
Workover for severe sanding wells
Sanding particlesForce analysis model on sanding particles
Critical sanding flow rate
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3. Dynamic data monitoring and interpretation (con’t)
Objective based modeling
geological dictionary (outcrops)
Seismic impedance
(interlayer thickness probability)Watered wells
2016.82015.10
2016.62014.3 2014.6
2016.62016.9
2016.10
2016.112015.8
2017.11
water breakthrough time
5.7 6.2
6.2
10.611.18.3
6.2
13.310.6
5.8
Chloride,104mg/L
Watering well analysis
Water monitoring and control is the key in gasfield operation
Watering wells concentrated on the edge of the reservoir anticline and near fault
locations
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3. Dynamic data monitoring and interpretation (con’t)
Watering patterns and watering early-warning technique
Established 4 reservoir watering pattern and their corresponding RTA type curves
Reservoir watering patters and their typical production curves
Watering early-warning technique based on rate transient analysis KES203
50
0
10
20
30
40
Ga
s P
rod
uc
tiv
ity
In
de
x (
(10
3m
3/d
)/(1
06k
Pa
2/
Pa
.s))
100000
0
20000
40000
60000
80000
p/Z
** (kP
a(a
))
7000 50 100 150 200 250 300 350 400 450 500 550 600 650
Cumulativ e Gas Production (106m3)
Legend
Flowing p/Z**
Productiv ity Index
Watering behavior on Blasingame typecurves Watering behavior on productivity index
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4. Numerical simulation
Numerical simulation
History matching: the simulation result matched the monitored dynamic data
Reservoir pressure simulation
Well production rate matched measured data
Reservoir gas saturation simulation Reservoir gas in place simulation
Reservoir pressured matched measured data
KS201 KS2-2-12 KS2-2-18
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5. Operation optimization
Optimized well allocation
Production wells on the structural crest, water drainage wells on the anticline edges
Place wells away from fracture concentrated zones, alleviating water coning
Simulation on different structural locations Simulation on fracture-matrix-well bore relations
Well 2Well 1keshen
0 100 200 300 400 500 600 700
0 100 200 300 400 500 600 700
6,6
00
6,7
00
6,6
00
6,7
00
0.00 305.00 610.00 feet
0.00 95.00 190.00 meters
File: KS-500md-30MPa-0-L-1.datUser: Z840
Scale: 1:4725Z/X: 3.00:1Axis Units: m
0
50
100
150
200
250
300
350
400
450
500
Permeability I (md) 2018-01-02 J layer: 26
keshen
0 100 200 300 400 500 600 700
0 100 200 300 400 500 600 700
6,6
00
6,7
00
6,6
00
6,7
00
0.00 305.00 610.00 feet
0.00 95.00 190.00 meters
File: KS-500md-30MPa-0-M-f15m.datUser: Z840
Scale: 1:4725Z/X: 3.00:1Axis Units: m
0
50
100
150
200
250
300
350
400
450
500
Permeability I (md) 2018-01-02 J layer: 26
keshen
0 100 200 300 400 500 600 700
0 100 200 300 400 500 600 700
6,6
00
6,7
00
6,6
00
6,7
00
0.00 305.00 610.00 feet
0.00 95.00 190.00 meters
File: KS-1000md-5MPa-0.datUser: Z840
Scale: 1:4725Z/X: 3.00:1Axis Units: m
0
100
200
300
400
500
600
700
800
900
1,000
Permeability I (md) 2018-01-02 J layer: 26
Measures on existing wells
Regulate pressure draw-down on wells at structural crest without watering
Water drainage operation on wells with mild watering problem, maximizing recovery
Watered-out wells on the anticline edge converted to water drainage wells
Regular sand flush overs on sanding wells and work over on sand-plugged wells
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6. Field development strategic planning decision making system
Multi-scenario gas supply analyzing model, to improve the planning feasibility
and flexibility
Full life circle economic evaluation for gas reservoirs, to determine economic
and technical strategies
Multi-scenario gas supply analyzing
model
Fast evaluation, profits focusing and risk control
Society significance
Profitability
Evaluationmodel
Raw data
Full life circle economic evaluation
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