Risk assessment on groundwater contamination from hydraulic - - PowerPoint PPT Presentation

Risk assessment on groundwater contamination from hydraulic fracturing and delamination

Modelling hydraulic fracture growth and wellbore delamination

Dane Kasperczyk, James Kear & Raman Pandurangan August 2018

Content

• Quick introduction to:

– Hydraulic fracturing – Wellbore delamination

• Why: The aims for the project
• Where: The case study regions for this project
• How: Statistical methods, mathematical models and input data
• Results: Model outputs
• Conclusions: Findings and where to next?

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Hydraulic Fracturing

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• Technique used to increase permeability
• Fracture growth is controlled by stress

– Grows perpendicular to least stress direction

Wellbore delamination

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• Vertical propagation of a crack (micro-annulus)

– Delamination between cement and casing or cement and rock boundaries – Can contribute to loss of well integrity

CSIRO Laboratory experiments designed to validate the model of micro-annulus growth. (Bunger et al. 2010) Simple schematic of a vertical well injector (not to scale). (Lecampion et al. 2013) Not a typical CSG well.

Rational for doing this project

Why? Aims?

Why

• Address community concerns around hydraulic fracturing

despite low/zero incidences of well failure due to hydraulic fracturing in Australia

• Improve hydraulic fracturing risk assessments

– Not using an artificial worst case scenarios – Avoiding a specific historical data for one area – it works like this over in the USA it will work here too, trust us

• Allow quantitative assessment of fracture growth

– Very Low/Low/Medium/High/Very High

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Aims

• Represent size of hydraulic fractures across entire case study

region

– Height growth – Lateral growth

• Quantify potential size of wellbore delamination from

– Micro-annulus crack growth during hydraulic fracture (0-2hours) – Micro-annulus crack allowed to grow to surface after CSG

decommissioning (0-฀)

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Case study regions

Queensland and NSW

Where

• Surat Basin

– Hydraulic fracture extent – Wellbore delamination

• Sydney Basin / Camden

Region

– Wellbore delamination

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Mathematical models

Hydraulic fracture and wellbore delamination analytical model

Modelling hydraulic fracture growth

11

Lateral growth Height growth

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Modelling wellbore delamination

• Based on Lecampion et al. 2013
• Driven by constant pressure fluid

injection

• Conservative

– No interface strength

• If we allowed the micro annulus to

grow to the surface

– How long would it take? – How wide would the crack be?

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Schematic of a vertical well injector (not to scale). (Lecampion et al. 2013). Not a CSG well.

Statistical method

Probability bounds analysis

Statistics!

• Probability / cumulative density function (CDF)
• Flip a coin
• Roll two dice – 6 sides with numbers 1,2,3,4,5,6 with a known CDF

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0.25 0.5 0.75 1 1 2 3

Cumulative Probability Sum of flipping (1-2) Coin

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 4 6 8 10 12 14

Cumulative Probability Sum of 2 rolled dice

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 4 6 8 10 12 14

Probability Sum of rolled dice

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 4 6 8 10 12 14

Probability Sum of 2 rolled dice – 6 sides – unknown 1-6 numbers

Probability Box

• Roll two dice

– 6 sides with unknown

numbers?

– Unknown number of dice?

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• P-box

– Probability that sum is 8 or

less is between 18% and 80%

– 95th percentile is between 9-

12

Input Data

• Data extracted from Queensland Qdex, NSW Digs, operator

information, company reports and literature.

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Injection rate 𝑛3/min 𝑅 Minmaxmean (0.96, 3.2, 1.6) Viscosity of injected fluid (cp) 𝜈 Minmaxmean (200, 235, 230) Total injection time (min) 𝑢 Minmaxmean (20, 120, 30) Treatment efficiency 𝜃 Minmaxmean (0.3, 0.5, 0.4) Injection depth (m) 𝐸 Minmaxmean (400,700,520) Height of pay zone (m) ℎ𝑔 Minmax(40,70) Casing diameter (mm) 2𝑆1 140, 178 Well diameter (mm) 2𝑆3 200, 216

Results

Hydraulic Fracture Growth

Hydraulic Fracture Growth

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Hydraulic fracture growth size at 99.9, 85th, 75th and 50th percentile

Hydraulic Fracture Growth

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Hydraulic fracture growth size at 99.9th and 50th percentile at whole of basin scale and specific scenario A with shorter injection time, lower injection rate.

Results

Wellbore Delamination

Micro-annulus growth during HF

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Micro-annulus crack length p- box in the Surat basin with a 178mm casing diameter.

Surat – 178mm Sydney – 140mm

50TH PERCENTILE

Min Max Uncertainty Min Max Uncertainty Length of Micro-annulus (crack) (m)

1 44 43 2 24 22

Fracture Opening (microns)

52 72 20 52 104 52

Fluid volume entering the micro-annulus during hydraulic fracturing (litres)

0.02 0.18 0.16 0.02 0.30 0.28

Micro-annulus crack length p- box in the Sydney basin with a 140mm casing diameter.

Micro-annulus growth post decommissioning

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Time for micro-annulus to reach Surface in the Surat basin.

Surat Basin Sydney Basin

50TH PERCENTILE Min Max Uncertainty Min Max Uncertainty

Time to reach the surface (days) 8 39 31 13 17 14 Fracture opening (µm) 20 32 12 32 35 03

Time for micro-annulus to reach Surface in the Sydney basin.

Findings and outcomes

Findings – Hydraulic Fracture Growth

• This study assessed hydraulic fractures growth across the Surat basin
• there is an 83% likelihood that the maximum fracture length would always be less than 500

meters

• and that 74% of fracture heights would always be less than 100m.
• Not an assessment on specific aquifer interaction. A future study could

combine this PBA model with a grid-based spatial method, to assess all subregions and their proximity to local aquifers.

• These measurements should not be taken as an exact measure under field

conditions, these are probabilistic top down values across entire basin, hydraulic fracture operations are monitored and fracture growth is suspended or abandoned when conditions or pressures cannot be maintained in a well.

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Findings – Delamination

• No significant delamination due to hydraulic fracturing in

petroleum wellbores was predicted. These findings are based on a conservative model that found a maximum of ~200ml of fluid in micro-annulus.

• Any potential micro-annulus growth after a well was

decommissioned would most likely have a width less than 50 microns

• Therefore the risk of significant contamination to overlying

aquifers from this mechanism is considered negligible for the Surat and Sydney basins

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Suggestions for future research

• Combine this PBA model with a

grid-based spatial method to simulate any point in the regions.

• This work focused on Australian

CSG – applicable to transfer this knowledge to shale, tight gas and

• ther deep coals plays, or other

fracture fluids.

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Thank you

Dane Kasperczyk Engineer t +61 3 9545 2411 e dane.kasperczyk@csiro.au w gisera.csiro.au