Optimization of a Groundwater Wellfield Subject to Regulatory Constraints

Transcription

1 Optimization of a Groundwater Wellfield Subject to Regulatory Constraints Andrew Hinnell, Ph.D., P.Geo. Senior Hydrogeologist, Advisian April 4,

2 Introduction Driver: Controls: Water supply Acts Regulations Guidelines Approach: Optimize water well production rates within the regulatory guidelines Advisian / 2

3 Groundwater Supply ~ 240,000 Water wells drilled in Alberta ~ 150,000 Water wells drilled since 1980 ~ 70,000 Active water wells within the Paskapoo Formation 330 million m 3 of groundwater 660,000 people rely on groundwater as their primary source of water (Alberta Environment 2010) Map credit: Advisian / 3

4 Regulatory Regime - Alberta Statute Water Act The purpose of this Act is to support and promote the conservation and management of water, including the wise allocation and use of water. Under the Water Act a licence is required to divert water for all purposes except household, traditional agriculture, or where use is exempt under the Water Regulation (e.g. fire fighting). Advisian / 4

5 Regulatory Regime - Alberta Implementation of the Water Act managed through Policy and Guidelines Groundwater Authorization Guideline (2011) Water Conservation and Allocation Policy/ Guideline for Oilfield Injection (2006) Groundwater Management Frameworks Advisian / 5

6 Groundwater Authorization Constraints: Sustainable Yield (Q 20 ) Q 20 = 0.7QH a s 20y T + s 100m O s 100m T Drawdown at the pumping well is limited to the top of the confined aquifer Impacts of the proposed water diversion on the Aquifer, the Environment, and Other Users needs to be assessed Advisian / 6

7 Synthetic Example Advisian / 7

8 Scenario Company A is evaluating their unconventional oil and gas asset and requires water to support the appraisal phase Having completed an Alternative Water Use Assessment groundwater was determined to be the preferred water source during appraisal with a switch to reuse/recycle of saline water should the asset move to operations Google Images Advisian / 8

9 Scenario Company A has drilled and tested multiple groundwater wells and is now interested in moving to licencing some groundwater wells to divert groundwater to support appraisal Questions: Which wells? How much? Advisian / 9

10 Setting Advisian / 10

11 Setting Well 4 Well 3 Well 2 Well 1 T=400m 2 /d S=1x10-4 Wells screened in a confined aquifer not connected to surface water Well Q20 rate Available Head Well Well Well Well Advisian / 11

12 Predicted Drawdown (Individual Q20) Well Rate Available Head Well Well Well Well Well A Well B Predicted Drawdown Total Q = 7,300m 3 /d Advisian / 12

13 Constraints Well interference within the well field reduces overall capacity of the well field H a 1 > s 1 1 +s 2 1 +s 3 1 +s 4 1 Drawdown at Wells A and B what interference is reasonable? s A > 0.1H a A s B > 0.1H a B 10% used as an example, actual values are subject to negotiation Advisian / 13

14 Predicted Drawdown (Well field) Well Rate Available Head Well Well Well Well Well A Well B Predicted Drawdown Total Q = 5,000m 3 /d Advisian / 14

15 Predicted Drawdown (Well field) Well Rate Available Head Well Well Well Well Well A Well B Predicted Drawdown Total Q = 1,200m 3 /d Advisian / 15

16 Optimization Multiple combinations of wells can meet constraints Which combination of pumping rates meets the constraints and results in the highest production rate for the well field? Advisian / 16

17 Optimization Multiple options based on complexity of problem and forward model DREAM - Efficient global MCMC even in high-dimensional spaces Advisian / 17

18 Optimized Production Rates Well Rate Available Head Well Well Well Well Well A 15 4 Well B Total Q = 5,500m 3 /d Predicted Drawdown Advisian / 18

19 Cost Considerations Well Rate Available Head Well Well Well Well Well A Well B Total Q = 4,900m 3 /d Predicted Drawdown Slight reduction in volume with significant reduction in cost (2 wells do not need to be tied in) Advisian / 19

20 Summary Objective: estimate the maximum volume of groundwater that could be produced from a wellfield given the regulatory constraints and thus identify a production rate that is defensible within the regulatory guidelines Approach: solve a constrained optimization problem for maximum production rate. Result: Maximum likelihood estimate of the production rate for each well that meets the specified constraints. From the groundwater licence applicant s perspective, this approach provides an estimate of total production rate for the well field and an estimate of proposed production rates from individual wells and a proposed well field operation scheme that meets regulatory constraints. Advisian / 20

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22 DISCLAIMER This presentation has been prepared by a representative of Advisian. The presentation contains the professional and personal opinions of the presenter, which are given in good faith. As such, opinions presented herein may not always necessarily reflect the position of Advisian as a whole, its officers or executive. Any forward-looking statements included in this presentation will involve subjective judgment and analysis and are subject to uncertainties, risks and contingencies many of which are outside the control of, and may be unknown to, Advisian. Advisian and all associated entities and representatives make no representation or warranty as to the accuracy, reliability or completeness of information in this document and do not take responsibility for updating any information or correcting any error or omission that may become apparent after this document has been issued. To the extent permitted by law, Advisian and its officers, employees, related bodies and agents disclaim all liability direct, indirect or consequential (and whether or not arising out of the negligence, default or lack of care of Advisian and/or any of its agents) for any loss or damage suffered by a recipient or other persons arising out of, or in connection with, any use or reliance on this presentation or information.