Optimization of a Groundwater Wellfield Subject to Regulatory Constraints Andrew Hinnell, Ph.D., P.Geo. Senior Hydrogeologist, Advisian April 4, 2017 www.advisian.com
Introduction Driver: Controls: Water supply Acts Regulations Guidelines Approach: Optimize water well production rates within the regulatory guidelines Advisian / 2
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
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
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
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
Synthetic Example Advisian / 7
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
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
Setting Advisian / 10
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 1 1600 8 Well 2 2600 10 Well 3 800 13 Well 4 2300 20 Advisian / 11
Predicted Drawdown (Individual Q20) Well Rate Available Head Well 1 1600 8 13.6 Well 2 2600 10 15.5 Well 3 800 13 12.8 Well 4 2300 20 14.2 Well A 15 8.5 Well B 5 8.6 Predicted Drawdown Total Q = 7,300m 3 /d Advisian / 12
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
Predicted Drawdown (Well field) Well Rate Available Head Well 1 900 8 7.5 Well 2 1000 10 9.6 Well 3 800 13 10.8 Well 4 2300 20 12.0 Well A 15 5.9 Well B 5 6.0 Predicted Drawdown Total Q = 5,000m 3 /d Advisian / 14
Predicted Drawdown (Well field) Well Rate Available Head Well 1 300 8 2.2 Well 2 400 10 2.5 Well 3 300 13 2.3 Well 4 200 20 2.0 Well A 15 1.4 Well B 5 1.3 Predicted Drawdown Total Q = 1,200m 3 /d Advisian / 15
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
Optimization Multiple options based on complexity of problem and forward model DREAM - Efficient global MCMC even in high-dimensional spaces Advisian / 17
Optimized Production Rates Well Rate Available Head Well 1 1100 8 8 Well 2 1300 10 10 Well 3 800 13 13 Well 4 2300 20 14 Well A 15 4 Well B 5 3.5 Total Q = 5,500m 3 /d Predicted Drawdown Advisian / 18
Cost Considerations Well Rate Available Head Well 1 0 8 7.1 Well 2 2600 10 10 Well 3 0 13 7.9 Well 4 2300 20 11.8 Well A 15 5.9 Well B 5 6.0 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
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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