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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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