candidate selection - overview

Candidate Selection - Overview

• The objective of candidate selection is to find the optimum stimulation candidates using accepted tools.

• Candidate progression involves grading those initial selections through a wellwork hopper to gain maximum impact.

• Application excellence makes the difference between success and failures on even the best wellwork candidates.

8/25/2015 1 George E. King Engineering

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Reasons for failures

• Many re-completion and re-stimulation jobs fail because the work was focused only on underperforming wells.

• Production data alone is not a basis for re-stimulation or other wellwork considerations.


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Know the Flowing System

Source – Chirag PTL 8/25/2015 3 George E. King Engineering

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The effect of damaged permeability layers in the

formation flow path. [ks* ke * (re/rw)] kavg = [ks * ln (re/rs)] + [ke * (ln re/rs)] kavg = avg perm thru the reservoir plus damaged layer ks = permeability thru the damaged layer ke = perm in the undamaged reservoir re = reservoir drainage radius of the well rs = radius of damaged (or stimulated zone) rw = radius of the wellbore


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Sources of the Best Wellwork • Reservoir

– Understand Channels

– Pressure Support

– Water and Gas control

– Infield drill

– Stimulate

– Inflow restrictions

– Waterblock

– Condensate Banking

– Bypassed pay

• Downhole – Lift

– Deliquification

– Deposits and restrictions

– Perf and Reperf

– Integrity Repair

– Friction limited

• Surface

– De-bottle

neck

– Choke

setting

– Gathering

line

– Separator

pressure

– Water and

gas

handling

• Injector

– Conforma

nce

control

– Fill

– Control of

x-flow

– Backflow

control

• Operations

– Up-time

– Optimizati

on

frequency

– Bean-up

Strategy

– Flux

Strategy


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What works the best?

• Look at the whole flowing system • Know your wellstock • What wellwork has been done? – what has worked,

what hasn’t, and why? • Identify the controlling limits or choke points. • Start with the best wells, but assess the poor wells

for anomalies • Look at all the opportunities and the options • Risk assess, rank opportunities and group work. • Timing, people availability, rig availability, access are

all important controls.


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Some Effective Parameters for Candidate Selection

Parameters used in

candidate selection

Importance How can it be

improved?

Recoverable

Hydrocarbon Reserves

What is remaining and

movable?

What can make it more

mobile?

Reservoir Pressure Pressure is the driving

energy

Floods, gas inj.,

Fh – porosity-feet A simple comparative

measurement of pay

quality

Well placement and

Reservoir contact :

laterals, fracs, etc.

Conformance Review Minimizes fluid

handling

Determine what fluids

are flowing & where

Lift optimization Ensures that the

maximum drawdown

can be placed on pay.

Survey the lift system

and check key

indicators.


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Common Traits of Successful Re-stimulation Re-Completion Projects.

1. Complex reservoirs (shales, coals, bedded, tilting, compartmentalized, discontinuous, etc.)

2. Low reservoir drive energy where water-flood or gas injection is possible.

3. Poor initial fracture design. Short fractures in tight gas reservoirs or low conductivity fractures in higher rate potential wells.

4. Opportunity for application of specialized technological advances, i.e., fit for purpose in a field.

5. Older wells that have been damaged by production of repair operations.

6. Wells with limited entry or limited wellbore-to-reservoir contact.


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Common Traits of Successful Re-stimulation / Re-Completion Projects.

7. Extremely thick zones of variable horizontal permeability and very low vertical formation permeability.

8. Infield Drilling Opportunities where fluid viscosity favors drilling (vertical or horizontal) over fracturing.

9. Cased, cemented and perforated completions in very high rate formations.

10. Wells with conformance control issues where water or gas can be controlled without reducing hydrocarbon flow.

11. Flow restrictions (chokes, small flow lines, excessive bends)

12. Well Repair – bringing on shut-in wells (integrity problems).

13. Reserve progression – Non-Proved to Proved-Developed.


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Complex Reservoirs

• Completions in complex reservoirs are usually the result of trial and error completions.

• Near-field and Far-field stresses may alter the direction of a frac once it leaves the near wellbore area.

• Polymers can damage coals and some shales. Inability to break polymers leaves the formation and the fracture pack damaged and low conductivity.

• The length of the fracture can be critical in effectively accelerating the production of


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Frac Length Variation with Permeability

The fracture length ranges are averages of what has typically been use,


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Frac Length Effect on Skin

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

FCD

Fra

ctu

re S

kin

Frac Length = 50 ft

Frac Length = 100'

rw = 10"

The FCD, or dimensionless fracture capacity, is a comparison of frac conductivity to that of the formation. Low skins are possible where the fracture is significantly more conductive than the formation – yet even in high formation permeabilities, fracturing benefits the production simply by breaking through the near wellbore damage.


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Rock Variability – what effect on flow?

• Permeability data from Permian dolomitized shallow-water platform carbonate outcrops in west Texas and New Mexico exhibit two to five orders of magnitude variability, most of which occurs within distances of a few feet [1 m] within single rock-fabric units. (SPE-65370 – Jennings)

• Fluid-flow simulations demonstrate that some long-range features control overall flow behavior even when short-range variability composes most of the variance. The short-range heterogeneities produce local smearing of displacement fronts.


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What is the source of the

well under-performance

problem? • Ineffective or problematic initial completion

– Problems from design, execution or damage, poor perfs, poor connection with reservoir (not matched to flow paths).

• Pressure depletion – Frac geometry change, loss of drive pressure, out-

gassing, loss of light ends, increasing deposits, water influx

• Damage during production operations – Deposits resulting from shear, temperature change,

out-gassing or mixing incompatible fluids (paraffin, asphaltenes, scale, salt, etc.)

– Phase changes from dew point, bubble point, water 8/25/2015 14

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candidate selection - overview

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