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? Groundwater contamination risk assessment | 28 August 2018 | 2

Hydraulic Fracturing ● Technique used to increase permeability ● Fracture growth is controlled by stress – Grows perpendicular to least stress direction Groundwater contamination risk assessment | 28 August 2018 | 3

Wellbore delamination ● 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. Groundwater contamination risk assessment | 28 August 2018 | 4

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 Groundwater contamination risk assessment | 28 August 2018 | 6

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- ฀ ) Groundwater contamination risk assessment | 28 August 2018 | 7

Case study regions Queensland and NSW

Where ● Surat Basin – Hydraulic fracture extent – Wellbore delamination ● Sydney Basin / Camden Region – Wellbore delamination Groundwater contamination risk assessment | 28 August 2018 | 9

Mathematical models Hydraulic fracture and wellbore delamination analytical model

Modelling hydraulic fracture growth Height growth Lateral growth Groundwater contamination risk assessment | 28 August 2018 | 11

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? Schematic of a vertical well injector (not to scale). (Lecampion et al. 2013). Not a CSG well. Groundwater contamination risk assessment | 28 August 2018 | 12

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 1 1 0.9 0.8 Cumulative Probability 0.75 Cumulative Probability 0.7 0.6 0.5 0.5 0.4 0.3 0.25 0.2 0.1 0 0 0 1 2 3 0 2 4 6 8 10 12 14 Sum of flipping (1-2) Coin Sum of 2 rolled dice Groundwater contamination risk assessment | 28 August 2018 | 14

Probability Box 1 1 0.9 0.9 0.8 0.8 0.7 0.7 ● Roll two dice Probability Probability 0.6 0.6 0.5 0.5 – 6 sides with unknown 0.4 0.4 0.3 0.3 numbers? 0.2 0.2 – Unknown number of dice? 0.1 0.1 0 0 0 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 Sum of 2 rolled dice – 6 sides – unknown 1-6 numbers Sum of rolled dice ● P-box – Probability that sum is 8 or less is between 18% and 80% – 95 th percentile is between 9- 12 Groundwater contamination risk assessment | 28 August 2018 | 15

Input Data Injection rate 𝑛 3 /min 𝑅 Minmaxmean (0.96, 3.2, 1.6) 𝜈 Viscosity of injected fluid (cp) Minmaxmean (200, 235, 230) 𝑢 Total injection time (min) Minmaxmean (20, 120, 30) 𝜃 Treatment efficiency Minmaxmean (0.3, 0.5, 0.4) 𝐸 Injection depth (m) Minmaxmean (400,700,520) ℎ 𝑔 Height of pay zone (m) Minmax(40,70) 2𝑆 1 Casing diameter (mm) 140, 178 2𝑆 3 Well diameter (mm) 200, 216 ● Data extracted from Queensland Qdex, NSW Digs, operator information, company reports and literature. Groundwater contamination risk assessment | 28 August 2018 | 16

Results Hydraulic Fracture Growth

Hydraulic Fracture Growth Hydraulic fracture growth size at 99.9, 85 th , 75 th and 50 th percentile Groundwater contamination risk assessment | 28 August 2018 | 18

Hydraulic Fracture Growth Hydraulic fracture growth size at 99.9th and 50 th percentile at whole of basin scale and specific scenario A with shorter injection time, lower injection rate. Groundwater contamination risk assessment | 28 August 2018 | 19

Results Wellbore Delamination

Micro-annulus growth during HF Micro-annulus crack length p- Micro-annulus crack length p- box in the Surat basin with a box in the Sydney basin with a 178mm casing diameter. 140mm casing diameter. Surat – 178mm Sydney – 140mm 50TH PERCENTILE Min Max Uncertainty Min Max Uncertainty Length of Micro-annulus 1 44 43 2 24 22 (crack) (m) Fracture Opening (microns) 52 72 20 52 104 52 Fluid volume entering the 0.02 0.18 0.16 0.02 0.30 0.28 micro-annulus during hydraulic fracturing (litres) Groundwater contamination risk assessment | 28 August 2018 | 21

Micro-annulus growth post decommissioning Time for micro-annulus to reach Time for micro-annulus to reach Surface in the Surat basin. Surface in the Sydney 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 Groundwater contamination risk assessment | 28 August 2018 | 22

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. Groundwater contamination risk assessment | 28 August 2018 | 24

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 Groundwater contamination risk assessment | 28 August 2018 | 25

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 other deep coals plays, or other fracture fluids. Groundwater contamination risk assessment | 28 August 2018 | 26

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