Using Modelling to Improve Wastewater Disposal Strategies

Transcription

1 Using Modelling to Improve Wastewater Disposal Strategies Gordon MacMillan, P.Geol. Matrix Solutions Jens Schumacher, M.Sc., Matrix Solutions Maxime Claprood, Ph.D., P.Eng., Matrix Solutions Michael L. Brewster, M.Sc. P.Geol., Devon Canada Matrix Solutions Inc. 1

2 Presentation Objectives 1) Complete the story of Grand Rapids disposal 2) Raise awareness of hydrogeology related disposal issues 3) Contribute to the rhetoric on the value of models Matrix Solutions Inc. 2

3 Presentation Objectives Every model math is wrong but some models math are useful Garbage in. math garbage out Models math are too time consuming to be useful Value of these statements can be tested by substituting model with math A x = b More useful clichés might be math Models provide a formal test of logic Models can support decision making Matrix Solutions Inc. 3

4 Introduction In-situ oil sands projects generate two wastewater streams that need to be handled. The most common approach to handling wastewater is downhole disposal. Poor selection of disposal zone can impair: 1) Bitumen recovery 2) Make-up water quality of wells in the same aquifer 3) Water quality of a non-saline aquifer Matrix Solutions Inc. 4

5 Introduction Wastewater disposal strategy can affect the project economics (SOR and CAPEX on disposal wells and pipeline) design Key Decisions 1) Aquifer selection 2) Number of wells 3) Pipelines and other infrastructure 4) Well placement 5) Distribution of rates Matrix Solutions Inc. 5 o o o Desired Outcomes Minimize cost Minimize risk Maximize regulator and stakeholder acceptance

6 Introduction If the modelling objective (question) is well defined, modelling can inform decisions and optimize the project design. d obs Key Decisions (m) 1) Aquifer selection 2) Number of wells 3) Pipelines and other infrastructure 4) Well placement 5) Distribution of rates Matrix Solutions Inc. 6 Φ m = d obs Fm 2 2 Numerical Model (F) Desired Outcomes (d obs ) Minimize cost Minimize risk Maximize regulator and stakeholder acceptance

7 Example 1 Wastewater disposal near a steam chamber Matrix Solutions Inc. 7

8 Example 1 Wastewater disposal near a steam chamber Problem: Steam chambers interact with bottom water aquifers. Wastewater disposal could inadvertently cool chamber and increase water handling. Matrix Solutions Inc. 8

9 Example 1 Wastewater disposal near a steam chamber Modelling Objective: Create a tool that can account for the interaction between the steam chamber and the aquifer. Identify areas of risk (i.e. areas sensitive to pressure change) Plan disposal strategies to match desired reservoir conditions Evaluate potential cumulative effects from other operators Matrix Solutions Inc. 9

10 Example 1 Wastewater disposal near a steam chamber Model Data: - 11 years of disposal or pumping at 50 wells - Transient pressures recorded at 50 observation locations - Large amount of geologic control: seismic; pre- Cretaceous unconformity; 6,261 well control points Model Approach: - Use high resolution McMurray Aquifer isopach - Include water imbalance at the SAGD pads as a source term - Use a fast 2D model to calibrate (15 min solution time) - Use a high degree of parameterization (1,800 adjustable parameters) to allow for potential heterogeneity Matrix Solutions Inc. 10

11 Example 1 Wastewater disposal near a steam chamber Matrix Solutions Inc. 11

12 Example 1 Wastewater disposal near a steam chamber - 50 source and disposal wells - Rates variable over time at all wells Matrix Solutions Inc. 12

13 Example 1 Wastewater disposal near a steam chamber Matrix Solutions Inc. 13

14 Example 1 Wastewater disposal near a steam chamber Matrix Solutions Inc. 14

15 Example 1 Wastewater disposal near a steam chamber Matrix Solutions Inc. 15

16 Example 1 Wastewater disposal near a steam chamber Calibrated transmissivities were relatively smooth and honored setting Some SAGD pads had a large influence on heads Model did good job of reproducing changes in head Matrix Solutions Inc. 16

17 Example 1 Wastewater disposal near a steam chamber Results - Water imbalance in SAGD chamber translates to water gain/loss in the aquifer - Transient head data is sensitive to this imbalance - Numerical model was able to reproduce and can be used to evaluate future operation strategies Identify areas of risk (i.e. areas sensitive to pressure change) Plan disposal strategies to match desired reservoir conditions Evaluate potential cumulative effects from other operators Matrix Solutions Inc. 17

18 Example 2 Wastewater migration toward make-up water supply wells Matrix Solutions Inc. 18

19 Example 2 Wastewater migration toward make-up water supply wells Problem: Wastewater disposal is planned in close proximity to a make-up water supply well and could affect water quality over time. Wastewater Disposal Matrix Solutions Inc. 19

20 Example 2 Wastewater migration toward make-up water supply wells 800 m 10 km Modelling Objectives: 1) Predict likelihood of wastewater breakthrough at make-up water well. 2) Predict concentration profile over time at makeup water well. Matrix Solutions Inc. 20

21 Example 2 Wastewater migration toward make-up water supply wells Model Data: - High resolution transmissivity field from 2D model - Facies characterization of areas to north and south - Vshale interpretations at 100 wells available as digital files - Salinity data from 107 logs - Pre-Cretaceous unconformity and other geologic knowledge Model Approach: - Use high resolution McMurray Aquifer transmissivities - Create a geomodel of hydrofacies in a one township area - Generate 50 stochastic geomodel realizations - MODFLOW predictions of wastewater migration in 22 geomodels - Use stochastic predictions of TDS to optimize disposal strategy Matrix Solutions Inc. 21

22 Example 2 Wastewater migration toward make-up water supply wells Above: 3D visualization of facies in 100 boreholes Left: vertical distribution of facies as volume fraction Right: One of two training images Matrix Solutions Inc. 22

23 Example 2 Wastewater migration toward make-up water supply wells 50 geomodel realizations honor hard data reflect geologic knowledge of channel orientation, meander, and width Reflect proportions of facies (e.g. 48% sand) Facies upscaled to 2.5 m tall by 75 m wide Matrix Solutions Inc. 23

24 Example 2 Wastewater migration toward make-up water supply wells 2D transmissivity field is exactly the same in each MPS model Regen disposal fluid predictions at source well ranged from 1 to 19% wastewater Non-MPS simulations predicted less than 2% wastewater Matrix Solutions Inc. 24

25 Example 2 Wastewater migration toward make-up water supply wells Results - Wastewater migration is highly dependent on geologic structure (i.e. connectivity of sand facies) - Single hydrofacies approach underestimates wastewater migration in this geologic setting - Numerical model was able to test alternative disposal strategies (e.g. rates and completion intervals) so that risk can be minimized Matrix Solutions Inc. 25

26 Example 3 Understanding physical setting in the context of Grand Rapids disposal Matrix Solutions Inc. 26

27 Example 3 Understanding physical setting in the context of Grand Rapids disposal Problem: High salinity area of the Grand Rapids is an attractive zone for wastewater disposal but is near non-saline area. Lower Grand Rapids Calculated TDS 4,000 60,000 (mg/l) Matrix Solutions Inc. 27

28 Example 3 Understanding physical setting in the context of Grand Rapids disposal Modelling Objective: Support decision making on the use of the Lower Grand Rapids Aquifer as a disposal zone by: 1) Evaluating regional structures and groundwater flow for a mechanism responsible for the high salinity 2) Evaluating the likelihood of wastewater impacting water quality in the non-saline areas of the aquifer. Matrix Solutions Inc. 28

29 Example 3 Understanding physical setting in the context of Grand Rapids disposal Model Data: - Regional scale characterization and model (Hayley et al. 2014) - 7 base flow estimates - Hydraulic head estimates at 1,359 DSTs and 444 wells - Transient heads at 147 locations responding to 10 years of water use (or disposal) Model Approach: - Use regional scale model to reproduce natural gradients and test for stagnation area - Use particle tracking to evaluate extent of wastewater migration and if the edge of the saline zone will move as a result of disposal Matrix Solutions Inc. 29

30 Example 3 Understanding physical setting in the context of Grand Rapids disposal Regional model: - Extends from ground surface to 50 m below pre-cretaceous unconformity - Includes 28 hydrostratigraphic units - Total volume of 15,000 km 3 discretized with 331,000 nodes Matrix Solutions Inc. 30

31 Example 3 Understanding physical setting in the context of Grand Rapids disposal Empress Channel Gross Isopach Lower Grand Rapids Hydraulic Head Matrix Solutions Inc. 31

32 Example 3 Understanding physical setting in the context of Grand Rapids disposal Lower Grand Rapids Calculated TDS 4,000 60,000 (mg/l) Matrix Solutions Inc. 32

33 Example 3 Understanding physical setting in the context of Grand Rapids disposal Zone of Relative Stagnation ~ 20 km Hydraulic heads in the Grand Rapids are strongly influenced by the Empress Channels and result in stagnant, high TDS, area Matrix Solutions Inc. 33

34 Example 3 Understanding physical setting in the context of Grand Rapids disposal 102/ W4 Relative to the McMurray Aquifer, the disposal zone sands are laterally continuous and homogeneous Particle tracking deemed sufficient to evaluate extent of wastewater migration Particle tacking completed during simultaneous pumping and injection and evaluated after 90 years Matrix Solutions Inc. 34

35 Example 3 Understanding physical setting in the context of Grand Rapids disposal Christina Channel Christina Channel No interference No interference predicted predicted Sunday Creek Channel Saline Water Interface Sunday Creek Channel Wiau Channel Wiau Channel Matrix Solutions Inc. 35

36 Example 3 Understanding physical setting in the context of Grand Rapids disposal Results - Area of hydraulic stagnation between Wiau and Sunday Creek channels correlates with area of high TDS - Single hydrofacies approach was used for wastewater migration in this geologic setting - Modelling results indicate zone can be safely used for wastewater disposal Matrix Solutions Inc. 36

37 Conclusions Matrix Solutions Inc. 37

38 Conclusions Wastewater disposal can pose a risk to project operations and the environment By effectively framing the problem and leveraging all valuable data modelling supported the following findings: Disposal near SAGD chambers has a causal link to SAGD water balance Extent of wastewater migration is highly dependent on geologic heterogeneity An aquifer not traditionally considered for wastewater disposal is an environmentally responsible option Matrix Solutions Inc. 38

39 Acknowledgements Christina Lake Regional Water Management Agreement (CLRWMA) partners: Devon Canada Corporation Cenovus FCCL Ltd. MEG Energy Corp. Rebecca Jacksteit, M.Sc., Cenovus FCCL Ltd. Scott Rayner, M.Sc., MEG Energy Corp. Beiyan Zhang, Ph.D., Matrix Solutions Inc. Louis-Charles Boutin, P.Eng., Matrix Solutions Inc. Kevin Hayley, Ph.D., P.Geoph, Matrix Solutions Inc. Matrix Solutions Inc. 39

40 Matrix Contacts Gordon MacMillan, P.Geol. Matrix Solutions Ph Jens Schumacher, M.Sc., Matrix Solutions Ph Maxime Claprood, Ph.D., P.Eng. Matrix Solutions Ph Matrix Solutions Inc. 40

41 References Hayley K., J. Schumacher, G. MacMillan and L. Boutin Highly parameterized model calibration with cloud computing: an example of regional flow model calibration in north east Alberta, Canada. Hydrogeology Journal (2014) 22: Matrix Solutions Inc. 41