Presentation 021110

8/19/2019 Presentation 021110

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Horizontal Wells: What WeKnow and What We Will

Never Know

Dr. S.D. Joshi

Joshi Technologies International, Inc.

Tulsa, OK 74135

Email: [email protected]

Website: http://www.joshitech.com

http://www.joshioilandgas.com


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Reservoir Applications

Naturally fractured reservoirs

Austin Chalk

Bakken Shale

Formations with water & gas coning

Gulf of Mexico

Elk Hills, California

Heavy oil reservoirs/Thermal application

California


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Reservoir Applications

Depleted gas/Gas storage reservoirs

Oklahoma

Texas

Low permeability shale gas reservoirs

Barnett, Woodford, Haynesville, Fayetteville,Marcellus, etc.

Waterflooding/CO2 flooding

California

East and West Texas


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U.S. Annual Horizontal Completions – Formation Summary

0

500

1000

1500

2000

2500

2007 2008 2009

YEAR

N U M

B E R O

F

C O M

P L E T I O N S

Bakken Barnett Cleveland Fayetteville

Haynesville Marcellus Woodford


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U.S. Horizontal Completions - State Summary


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History of Horizontal Drilling

Short radius drilling

Medium radius, 1985

Downhole mud motors

Re-entry drilling, 1995

Coiled tubing drilling(underbalance drilling)


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History of Horizontal Drilling

RSS: Rotary Steerable System

Fracture stimulation of horizontal wells

Open hole fracturing

Cased hole fracturing

Simo fracs


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Productivity Improvement Factor Distribution of Productivity in 96 horizontal wells


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Horizontal Wells Drilled in Western Canada

(1988-2001)


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The productivity improvement factor (PIF)ranges from 3 to 5. The short term PIF = 4.

The long term PIF = 1.8.

After 5 years of production, the cumulative oil

production from horizontal wells is about 2times greater than the cumulative production

from vertical wells.

About one in three horizontal wells has been

an economic failure. Thus economic successrate for horizontal wells is 66%.

Comparison of Horizontal and Vertical Wells


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Review the Field Results

Horizontal wells are mostly developmental(in-fill) wells

Commercial success ratio is 65 to 80%

Commercial success rate

Oil & gas price

Production rate


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North Slope, Alaska


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Bakken wells: 2008(8 fractures per well)

0

200

400

600

800

1000

1200

I

. P .

( B O P D )

1 2 3 4 5 6

VARIOUS WELLS IN BAKKEN SHALE

INITIAL PRODUCTION RATES


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Horizontal Well Rates

Stabilized rates of horizontal wells are 2 to 4fold more than stabilized rates of verticalwells.

Rates of fracture stimulated wells are 5 to 11times more than conventional wells.


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Horizontal Well Rate:

Important Parameters

Producing well length (Not the drilled length)

Formation damage/stimulation

kv/kh (vertical to horizontal permeability)

Reservoir permeability, kh


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Horizontal Well Rate:

Important Parameters

3 additional unknowns in fractured horizontal wells:

Number of fractures (producing)

Fracture conductivity

Fracture length


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Measurements

What can we measure?

Well rate

Well testing ( If practical)

Build up or drawdown


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Early Times Late Times

Horizontal Pseudo-Radial FlowVertical Radial Flow

mqB

k k Lv y1

162 6

. k v

k x

k y

Field Units

Metric Units Replace constant ‘162.6’ by ‘2.149 x 106’ in above equations

hk k

qBm

y x

6.1623

Horizontal Well Testing

Concepts


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Maximum three measurements

Rate

Slopes m1 & m3

We have at least 4 unknowns and

possibly 7 unknowns

Producing length, kv/kh, kh,

Skin factor ,Sm (damage or stimulation)

Results


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Results

Every answer is a right answer!


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Multiple Wells in The SameReservoir

Most reservoir properties show log normaldistribution. Therefore, productivity of several

horizontal wells drilled in the same reservoir

would also show a log normal distribution.


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Sandstone Reservoir

98959080502052 101

10

100

PROBABILITY (%)

P R O D U C T I V I

T Y

I N D E X

( B O P D / P S I )


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Log-normal Distribution of

Horizontal Well Productivities

98959080502052 100.1

1

Probabili ty (%)

P R O

D U C T I V I T Y

I N D E X

( B O P D / p s

i )

Sandstone Reservoir


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Reasons for Failure

Mechanical

Casing collapse, well collapse

Sanding & bridging of liner

Hole collapse after well stimulation

Difficulty in installing liner especially inmultilateral wells

Highly ‘sinusoidal’ well shape

Wrong well trajectory: drilling in unproductivezone, drilling in the water zone etc.


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Reasons for failure

Mechanical, continued

Pressure drop from toe to heel of a horizontal well

Difficulty in fracture initiation

Screen out of fractures


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Pressure Drop in aHorizontal Well

%10:Desirable Dpipe

pp


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Senlac/Winter Cummings/Dina

Pool, Canada


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Reasons for Failure

Geological /Reservoir

Formation damage: production from a horizontal

well is less than the nearby vertical wells

Reservoir heterogeneity (Producing length shorterthan the drilled length)

Economic failures

Low product prices


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CO2 WAG

HorizontalInjection Wells

South Cowden Unit,

Texas


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Gamma Ray - tool or other lithological toolson MWD assembly

Lithological logging

Production logging

•slotted liner completion (?)

Estimate from well test

Mud log

Measurement of Length


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Well Rate and

Producing Length

Double the producing length of a well and theproduction rate will increase by a factor of 1.44

Reduce producing well length by a factor of 4

and production rate will decrease by a factor of 2


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Permeability Ratio, kv/kh

Core data

kv/kh is generally an estimate

Geological literature for median length of

shale barriers

offshore bars (10 met long)

deltaic environment (400 met long)


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Continuity of Shale Intercalations as a

Function of Depositional Environment


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Reserves

Horizontal well reserves?Horizontal well flow

Initially transient flow

Once well encounters boundaries

Decline ( Steady State or Pseudo steady state Flow)


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660’

L

2000’

1320’

2xeh = 3,3202xev

2yev

1320’

2yeh

Vertical Well

Drainage Area = 40

Acres

xev/yev = 1

Horizontal Well

Drainage Area = 100

Acres

xeh/yeh = 2.5

Reservoir with Uniform HorizontalPermeability (ky/kx = 1)


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Anisotropic Reservoirs

If we drill a horizontal well along the low

permeability direction (perpendicular to the high

permeability direction) then the horizontal well

drainage area will be significantly larger than theconventional well drainage area.


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4174’

209’417’

2xev 2xeh=2417’

2yev

L=2000’

ky/kx = 100

Vertical Well

40 Acre Drainage Area

xe/ye = 0.1

Horizontal Well

232 Acre Drainage Area

xe/ye = 0.58

2yeh

Drainage Area


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Producing Characteristics & Recovery

for Vertical and Horizontal wellsin Austin Chalk, Niobrara and Bakken formations


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Review the Field Results

Reserves are difficult to estimate if wells are

(initial flow period) in transient flow.


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Single Phase Flow


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Type Curve for a Horizontal Well in the

Center of a Square Drainage Area


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Bakken Shale Example

5000’ Horizontal Well

8 Fracs

7744 psia Reservoir Pressure at 10780’

42’ Pay

8% Porosity

0.08 – 0.006 md Permeability

640 acre drainage area

14 years to Pseudo-steady state with 0.08 md !


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Bakken Shale Example

Exponential DeclineBakken Shale Exam ple Expon ential Decline

1

10

100

1,000

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000Cumlative Oil, stb

O i l R

a t e ,

s t b / d

Data

Decline Fit


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Bakken Shale ExampleBakken Shale Exam ple Decline

1

10

100

1,000

1,000 10,000 100,000 1,000,000

Cumlative Production, stb

O i l R

a t e ,

s t

b / d

Data

Decline Fit


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Bakken Shale ExampleBakken Shale Exam ple Decline

1

10

100

1,000

10 100 1000 10000

Time, days

O i l R

a t e , s

t b / d

Data

Decline Fit


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Bakken History MatchBakken Shale Exam ple

0

100

200

300

400

500

600

700

800

0 50 100 150 200 250 300

Time, days

O i l R

a t e , s

t b / d

Data

8 Fractures 80'

4 Fractures 200'


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What We Know

1. Production rate

2. Drilled length

3. Number of fracture jobs


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What We Do Not Know

1. Producing well length2. kv/kh, Ratio of vertical & horizontal

permeability

3. Number of producing fractures

4. Effective fracture conductivity

5. Reserves in the transient flow period


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Conclusions

Horizontal well analysis requires engineering

judgment

It is difficult to get unique answer

Reserves are difficult to estimate during the

transient flow.

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