Evaluation of flow potential in the overburden Georg Röser

2014-10-30 Classification: Open

P&

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30.1

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014

Outlook

1. The problem at hand

2. Legal framework and requirements

3. Scope of the project

4. Flow potential in low-impermeable formations

5. Proposed workflow during well planning

6. Summary

2014-10-30 2 Classification: Open

3

1. The problem at hand

• Statoil is looking at ~1200 wells for permanent P&A

• A project was initiated to look into cost efficient

P&A solutions

• Strict requirements regarding potential

permeable zones in the overburden

will lead to extra barriers and thus

cost a lot of money!

• Hence a sub-project on the evaluation

of permeable zones in the overburden

was initiated.

2014-10-30 Classification: Open

2. Legal framework and requirements

4

NORSOK D-010

9.3.1 Design basis, premises and assumptions

“All sources of inflow shall be identified and documented.”

→ we need to find them… all of them!

9.6.2 Well barrier acceptance criteria

“Permanently abandoned wells shall be plugged with an eternal perspective taking

into account the effects of any foreseeable chemical and geological processes.”

→ how to define “eternity”…?

→ how to cover any eventuality…?

2014-10-30 Classification: Open

TR3507

In drilling and well activities any formation shall be considered to be a potential source of inflow

with overpressure and/or HC present, unless otherwise can be concluded.

A formation shall be considered to be a potential source of inflow and consequently must be

regarded as a reservoir if:

1. The formation contains free gas

2. The formation contains movable hydrocarbons

• Hydrocarbons are normally movable unless they are residual or have extremely high viscosity (i.e. tar)

3. The formation contains movable water with overpressure, unless the risk (probability

and consequence) of an inflow is considered to be insignificant. An assessment of risk

shall include a quantitative evaluation of:

• Flow potential; volume, matrix permeability and fractures

• Potential consequences associated with flow to overlaying formations and/or the environment.

5 - 17

2. The legal framework and requirements

2014-10-30 Classification: Open

3. Scope of the project

• Definition of the term “flow potential” in low-/impermeable

zones of the overburden; describe a work

process/procedure to identify flow potential.

• Assess uncertainty in porepressure estimates in the

overburden.

• To which degree can experience be transferred across

fields, is it possible to establish general statements about

some formations across larger areas?

• A medium/long-term task is to challenge the existing

requirements.

• External study ongoing on risk based leak criteria for wells

(DNV)

6 2014-10-30 Classification: Open

4. Flow potential in low-impermeable formations

1. Ruling factors for flow potential in low/impermeable overburden formations

− Permeability logs, core

− Pressure pressure points/MDT

− Volume available connectivity, lateral extent

− Fluid type scanning/sampling

− Temperature direct temperature measurements

− Time consider different time spans

Difficult to define cut-off value for flow potential

due to combination of affecting factors.

7 2014-10-30 Classification: Open

4. Flow potential in low-impermeable formations

2. Identification of problem zones

− Data acquisition at different operational stages of a well (drilling, production, P&A)

− Zones with possible flow potential often don’t show on standard datasets alone

− Additional data acquisition (NMR, pressure/inflow testing, seismic, laboratory testing)

− The Statoil internal “Overburden Management Project” recommends to extend standard

data acquisition in the overburden to include NMR (FMI) and inflow testing (MDT, mini-

DST) in the future.

8 2014-10-30

GR DEN/NEU DTS/DT RT NMR – T2 POROSITY K comp GR -spectral

This zone was never thought of as a possible zone of influx, but

was discovered by shear (un)luck because it was decided to log

the whole section with NMR-tool – not just the already known

zones of interest!

Classification: Open

4. Flow potential in low-impermeable formations

3. Sensitivity study regarding flow potential in different sized reservoirs and varying fluids

9 2014-10-30

Hydrocarbon mass

Original in placeProduced during depletion

from 200 bar to 199 bar

[kg] [kg]

Oil, 100m•100m•0.35m 362329 1812

Oil, 100m•100m•1m 1035226 5176

Oil, 100m•100m•5m 5176129 25881

Oil, 1000m•1000m•0.35m 36232903 181165

Oil, 1000m•1000m•1m 103522581 517613

Oil, 1000m•1000m•5m 517612905 2588065

Gas, 100m•100m•0.35m 83216 416

Gas, 100m•100m•1m 237760 1189

Gas, 100m•100m•5m 1188800 5944

Gas, 1000m•1000m•0.35m 8321600 41608

Gas, 1000m•1000m•1m 23776000 118880

Gas, 1000m•1000m•5m 118880000 594400

Classification: Open

5. Proposed workflow during well planning

10 2014-10-30 Classification: Open

6. Summary

• Very strict requirements – “zero flow for eternity”

• Possible high impact on cost savings during P&A

• Main challenges connected to…

− definition of flow potential as it is affected by many different factors

− localizing zones that need to be plugged

• Sensitivity study shows volumes in place to be one of the most critical factors

→ however very difficult to assess in overburden formations (geometry, lateral

extent)

• Workflow proposed to optimize identification of zones with flow potential in a well’s

life cycle from exploration to PP&A.

11 2014-10-30 Classification: Open

Evaluation of flow potential in the

overburden

Georg Röser Discipline Leader Operations Geology GEOP STJ

E-mail address georos@statoil.com

Tel: +47 915 75 627 www.statoil.com

12 2014-10-30 Classification: Open