Assessing Production and Injection Effects• DST results are directly influenced by test conditions as well as the

hydrogeological conditions in the vicinity of test.• Even for good quality tests, there are still a number of issues in

measuring formation pressures such as presence of production/injection wells in the vicinity, inaccuracies in the position of thegauges, gas/hydrocarbons, or fluid variations.

• DST measurements must be reviewed and culled carefully in order todetermine the best estimate of the formation pressure. CumulativeInterference Index (CII) methodology can be implemented to identifythe production /injection influences.

• The CII methodology assumes that for production influences, inanalogy to water­well testing principles (Bruin and Hudson, 1961;Tóth and Corbett, 1986) the effect is directly proportional to aninference index, log(t/r2). Here 't' is the length of time, in years, sinceproduction started before the pressure measurement and 'r' is distancebetween the production wells and the well where the pressure wasmeasured.

• The CII index for a particular DST is the cumulative sum ofinterference indices for pumping/injection wells in the surroundingregion.

Variable Density Flow EffectsRegional groundwater flow in majority of sedimentary basins aroundthe world has traditionally been studied using:• Freshwater hydraulic heads.• Pressure­depth plots.These methods assume that the density variations within the formationare negligible. However in practice the density driven flow can beimportant in aquifers with dense brines, large dip, or small hydraulicgradient. This study implements a Water Driving Force (WDF)approach (i.e. a vectorial analysis to identify flow directions in regionswhere density­driven flow is important and can change the inferredmagnitude and direction of flow).

IntroductionThe Alberta Geological Survey's(AGS) Groundwater Program isfocused on identifying,characterizing and quantifyingAlberta's groundwater resources.Characterization and mapping ofdeep groundwater resources isbecoming increasingly importantas the Government of Albertaimplements its WaterConservation Policy seeking tominimize freshwater use.

Advancing Methods for Hydrogeological Characterizationof Deep Aquifers in Sedimentary Basins

Amandeep Singh, Dan PalombiAlberta Energy Regulator­Alberta Geological Survey402, Twin Atria Building,4999­98 AvenueEdmonton, Alberta, Canada,www.aer.cawww.ags.gov.ab.ca

H11D­0904

Conclusion• As industry in Alberta moves to utilize more saline water, a more

comprehensive understanding of deep groundwater will be requiredto manage and allocate water resources in the province. Currentwork focuses on developing existing methodologies to map regionalgroundwater flow across large areas in a mature sedimentary basin.

• CII methodology provides the user a tool to identify and cull outpotentially erroneous production influenced pressuremeasurements, in order to map distributions of hydraulic headunaffected by production influences. The methodology can also beused to map present­day (after production) hydraulic headdistribution.

• The WDF methodology assists in identifying the regions of anaquifer where density driven flow needs to be taken into account.The methodology implements a vectorial analysis to identify flowdirections in these regions where density can change the inferredmagnitude and direction of flow.

Case Study• A case study for the

area spanning across 4Alberta township (032­8­W­4 to 032­10­W­4)is presented withineastern Alberta.

• Figures to the rightshow the head mapfrom the raw data setand the head map fromthe culled data set,illustrating thedifferences and needto cull the DST datasetfor quality andproduction influences.

Hydraulic Head map (culled data using CII)

Water Driving Force (WDF)Based on Hubbert's (1940) and Davies (1987) work the "Water Driving Force" canbe defined as

where, h is the freshwater hydraulic head, Δρ is thedensity difference between in­situ brine and freshwater,ρ is the density of freshwater, and E is the elevation ofthe aquifer base.• In equation (1), the first term represents the force due to potential gradient whereas

the second term represents the force due to buoyancy.• The equation represents the addition of two vectorial terms, which gives the net

driving force on the formation water at a particular point.• In situ brine density is calculated as a function of pressure, temperature and total

dissolved solids (TDS) using Chierici (1994) equation of state.

Case Study• A case study is presented for the illustration of WDF implementation. The aquifer

presented is the Duperow aquifer from the Williston Basin.The aquifer has amaximum thickness of 150m and is composed of limestones/dolostones alongwithlayers of sandstones, siltstones and shale belonging to the Upper­Devonian system.

Hydraulic Head map Structure map

Results• Figure to the right

shows the water densitymap for the Duperowaquifer. The mapshows that the densityis higher in the south­east part of the domain.

• Figure below showsthe vector map forWDF and the anglebetween WDF vectorand head vector. Thearrows show the forceacting on water and thecolour demonstrates theWDF angle with respect to the head vector. The figure demonstratesthat the WDF method can help identify the regions where densitydriven flow should be taken into consideration and the approximatedirection of water driving force.

Water density map (kg/l)

Cumulative Interference Index (CII)C­code was developed for implementing the CII methodology ( A.I.Alkalali, and B.J. Rostron, 2003).• Methodology implemented uses a

parameter “R”, the search radiusfrom DST location within whichthe production wells are includedin CII calculation.

• CII value of zero indicates noproduction effect (i.e. no wellswithin the search radius before thetest) and the value of 1 indicatesDST at the production location.

CII Implementation

Input­ DST data, Production well data,Parameter 'R'

Output­CII, Wells within 'R'

CII methodology

Temperature map

Salinity map

Pressure map

Acknowledgements

Water driving force magnitude and direction

WDF implementationTwo methodologies are presented inthis work.1. Improving the data quality for

pressure measurements in deeper (>4000 mg/l) units used for mappinghydraulic heads. Drill stem testing(DST) or pressure­transient testing isan oil and gas exploration procedureto determine the fluids present andthe rates at which they can beproduced from a formation. Thefocus here is to identify the DST'spressure measurements influencedby nearby production/ injection.

2. The Water Driving Force (WDF)methodology to takes into accountthe density variations in hydraulichead mapping for deeper aquifers.This study implements a vectorialanalysis to account for densityvariations which are often neglectedin conventional analysis.

Geological Mapping

3D geological Modelling

Hydrostratigraphy

Distributions andPatterns of Salinity

and Hydraulic Heads

Variable Density FlowEffects

Workflow for hydrogeologicalcharacterization of deep aquifers

Python Script

Inputs­ Structure of confining unit, head, temperature,salinity and pressure grids

Outputs ­Waterdensity map, WDFdirection/magnitudemap, Aspect difference(WDF ­ strucure slopeand WDF­ headgradient)

Contact: amandeep.singh@aer.ca

Hydraulic Head map (raw data)

Duperow Extent

Aspect differencebetween WDF andhead vector