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Evolution of 3-D Geologic Framework Modeling and Its Application to Flow Studies

In this Fact Sheet, the authors discuss the evolution of project 3-D subsurface EXPLANATION OKLAHOMA framework modeling, research Arbuckle-Simpson in hydrostratigraphy and airborne Arbuckle-Simpson , and methodologies Trinity used to link geologic and Edwards-Trinity models. Edwards Edwards recharge TEXAS area boundary

Edwards-Trinity Trinity

he various geologic processes thatT shape the ’s surface and sub- surface all operate in three-dimensional (3-D) space. Within the U.S. Geological Survey (USGS), the greatest needs and Edwards applications for 3-D modeling include 0 125 250 375 500 KILOMETERS the following: (1) visualization of surface 0 125 250 375 500 MILES into the subsurface, (2) inter- pretation and verification of the geology and its controlling structures, and (3) application of 3-D model data for Figure 1. Location map of the Arbuckle-Simpson and Trinity aquifers and Edwards aquifer investigating geologic issues (Jacobsen recharge area. and others, 2011). Three-dimensional geologic modeling Three-dimensional geologic framework models can be directly converted into of an aquifer can quantitatively depict groundwater flow models, such as MODFLOW. Construction of the 3-D geologic archi- the connectedness of units across tecture of an aquifer needs to be the first step in using geologic properties to constrain fault and fracture zones. This model- groundwater flow models. This first-step approach takes much of the subjective guess- ing allows to determine the distribution of geologic units, structural work out of constructing model layers and results in a model that is more realistic and features, and other controlling factors, representative of the actual subsurface hydrologic conditions of the groundwater basin such as and permeability. being modeled. These parameters are complex vari- Several USGS projects, supported by the National Cooperative Geologic Mapping ables that reflect original depositional Program (NCGMP), are using multidisciplinary approaches to reveal the surface and conditions, alteration, dissolution, and subsurface geologic framework of three important groundwater aquifers: the Edwards, dislocation. Geologic 3-D framework Trinity, and Arbuckle-Simpson (fig. 1). In this Fact Sheet, the authors discuss the evolu- modeling also is useful for visualizing tion1 of project 3-D subsurface framework modeling, research in hydrostratigraphy and the interactions of fault and related airborne geophysics, and methodologies used to link geologic and groundwater flow structural features. models.1 The principal sections of this Fact Sheet are as follows: 21 Ratio of the volume of voids in a Geologic Framework of the Edwards and Trinity Aquifers porosity material to the total volume of the 21 Geologic Framework of the Arbuckle-Simpson Aquifer Rate of flow of a through a 32 permeability porous material 2 Arbuckle-Simpson 3-D Geologic Framework Model to Groundwater Flow Model Freely available USGS 3 MODFLOW software to simulate the flow of groundwater through aquifers 43 Arbuckle-Simpson MODFLOW Model 43

U.S. Department of the Interior 4 Fact Sheet 2012–3106 Printed on recycled paper U.S. Geological Survey 4 October 2012 1

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1 Geologic Framework of the Edwards and Trinity Aquifers 2 Geologic Framework of the Arbuckle-Simpson Aquifer

The Edwards aquifer in Texas is one of the most productive freshwater The Arbuckle-Simpson aquifer of south-central Oklahoma (fig. 1) encompasses more than aquifers in the world. It has been designated a sole source aquifer by the 850 square kilometers and provides for public drinking supply, farming, mining, conservation, U.S.3 Environmental Protection Agency (EPA) and is the primary source of water and5 recreation. The aquifer also contains a number of unique freshwater and mineral springs, such as for San Antonio, the Nation’s seventh largest city. Understanding the Edwards is Buffalo (fig. 4), in the Chickasaw National Recreation Area. essential for maintaining habitat for several threatened and endangered species. The aquifer’s eastern groundwater basin (Hunton anticline area, fig. 5) has been designated a sole The Trinity aquifer forms the catchment area for the Edwards aquifer, and it 560000 source aquifer by the EPA. Proposed development of water supplies from the aquifer led to concerns intercepts some surface flow above the Edwards recharge area. The Trinity aqui- 555000 that large-scale withdrawals of water would cause decreased flow in and springs, which in turn fer also may contribute to the Edwards’ water budget by across 4 550000 could result in the loss of supplies, recreational opportunities, and aquatic habitat. formation boundaries at considerable depths. Dissolution, development, and The Oklahoma Board, in collaboration with the Bureau of Reclamation, the 3288000 545000 faulting and fracturing in both of these carbonate-rich aquifers directly control USGS, Oklahoma State University, and the University of Oklahoma studied the aquifer to determine aquifer geometry by compartmentalizing the aquifer and creating unique ground- 540000 the volume of water that could be withdrawn while protecting springs and streams. The USGS water flow paths. 3280000 2 535000 NCGMP, in cooperation Three-dimensional modeling studies of aquifer-bearing units in south-central EXPLANATION with the USGS Oklahoma Texas concentrated on the area’s carbonate-rich hydrostratigraphic units, and Elevation control points 530000 Water Center underscored the importance of airborne electromagnetic data for defining new 3272000 Picks Geology map relations (colors and other Federal and unit contacts and fault structures (Blome and others, 2006). Two 3-D models 525000 for various units) State agencies, supported discussed5 as follows highlight key controls on aquifer permeability and provide insights on subsurface aquifer processes and aquifer boundaries and interfaces. construction of a 3-D EV The proprietary software EarthVision (EV) was used because of its ability to Figure 2. Three-dimensional model of northern Bexar framework model of the combine various data types and accurately define faulted surfaces while main- County, Texas (Pantea and Cole, 2004). water-producing Hunton taining stratigraphic and structural integrity and complexity. anticline area. Construction The 3-D EV model of northern Bexar County (fig. 2) reveals the subsur- of the model was chal- face geology and groundwater flow units of the Edwards and Trinity aquifers, lenging due to the folded, where water range from 60 to over 300 meters in depth. This 3-D model faulted, and fractured nature is based on mapped geologic relations that of the Hunton anticline reflect: (1) Balcones fault zone structures, geology (fig. 5), variable (2) detailed interpretations of 40 principal wells, unit thicknesses (from and (3) gross geometry of the Edwards Group 600 to 2,750 meters), and hydrostratigraphic units derived from prior Figure 4. Buffalo spring, Chickasaw National Recreation Area, south-central interpretations of depositional environments and scarcity of well information. Oklahoma. paleogeography. The 3-D model was also con- structed to determine whether hydrostratigraphic units could be accurately modeled in the sub- surface and to visualize the lateral connections between hydrostratigraphic units of contrasting 97°00' 96°50' 96°40' 96°30' 34°40' EXPLANATION permeability across fault strands. uplift A 3-D EV model of the rock units of the GARVIN Lawrence Model extent of Hunton Chickasaw National MURRAY FFZ anticline area Recreation Area

Edwards and Trinity Groups in the north Seco COAL Structures FFZ Franks fault zone Creek area of Medina and Uvalde Counties, Texas PONTOTOC All mapped faults CFZ Clarita fault zone 464000 BFZ Bromide fault zone (fig. 3), was constructed using a variety of digital 3265000 Modeled mapped faults Hickory syncline Modeled inferred faults SFZ Sulphur fault zone datasets, such as: (1) geologic maps, including SSF South Sulphur fault Hunton Geology the current geologic map of the area (Blome and anticline MCFZ Mill Creek fault zone 34°30' CFZ Post-Simpson rocks RF Reagan fault UTM coordinates SulphurSFZ others, 2004); (2) lithologic descriptions, interpre- syncline Simpson Group outcrop 3260000 tations, and geophysical logs from 31 drill holes; SSSSFF Arbuckle and Timbered (3) helicopter electromagnetic geophysical data Belton SFZ Hills Groups outcrop UTM coordinates anticline Mill Creek BFZ Geology outside 3-D (Smith and others, 2003); and (4) known major and syncline MCFZ model extent minor faults in the study area. This model reveals RRFF 472000 County boundaries the complex intersections of both major and minor 3255000 faults in the subsurface, and the impact these faults 34°20' CARTER JOHNSTON have on the continuity of the Trinity and Edwards 0 5 10 KILOMETERS aquifer-forming units. 0 5 10 MILES

Body of rock that forms a hydrostratigraphic unit distinct hydrologic unit with Figure 3. Three-dimensional model of the north Seco Creek area of Medina and Uvalde Figure 5. Geology of the Arbuckle-Simpson aquifer’s Hunton anticline area, south-central Oklahoma (outlined in the flow of groundwater Counties, Texas (Pantea and others, 2008). Multiple fault structures (shown in red) blue), and its major and minor fault structures (Faith and others, 2010). and electromagnetic geophysical profiles (shown as blue and gray fences) were used Ability to emit or transfer to construct the model. electromagnetic energy in the form of electromagnetic waves model surfaces. The topoftheSimpson surface, whichwasusedtodefineother resents themodel’s primaryreference field geologymapping techniques. and detailunachievablebyusing traditional (fig. 7)representsrockunitswith clarity southwestern flankoftheHunton anticline resistivity overonesurveyblock onthe springs inthewest. A mapofapparent freshwater springsintheeastandsaline and (4)tomapthetransitionbetween outcrops ofthelithostratigraphicunits, surface expression,(3) shallow faultsthathavenorecognizable cisely locatemappedfaults,(2)toidentify 2011), wereusedasfollows:(1)topre electromagnetic survey(Smithandothers, missing becauseoferosion. of themodelarea,post-Simpsonrocksare of thedigitalelevationmodel.Overmuch top oftheSimpsonGroupandsurface unit wasdefinedasthevolumebetween a knowncontact. The post-Simpsonmodel jected basedonthex-,y-,andz-valuesof Group andbasementmodelunitswerepro pre-erosional surfacesfortheSimpson Group wasidentifiedin54 was pickedfrom89 top ofthe Arbuckle-Timbered HillsGroup defined usingdatafrom13drillholes. The (1996). The topofthebasementwas the geospatialmapdatabaseofCederstrand geologic mappingbyJohnson(1990)and and faultsweredefinedfromthesurface and petroleumwells. logs, cores,andcuttingsfrom126water surfaces wereobtainedfromgeophysical data usedtodefinethemodelandmodeled water-bearing unitsoftheaquifer. The (dark pink)rocks,whicharetheprimary Groups (lightpink)andSimpsonGroup extents ofthe Arbuckle and Timbered Hills The model(fig. anticline area(Faithandothers,2010). Arbuckle-Simpson aquiferintheHunton of fourhydrostratigraphicunitsthe structed toquantifythegeometricrelations Geophysical data,includingahelicopter The modelstratigraphiccontacts This 3-Dframeworkmodelwascon

6) showsthevolumetric

drill holesandrep

to refinethe

wells. Locally, - - - - Figure 7. in figure7. model. Thewhitepolygonoutlinestheareaofhelicopterelectromagneticsurveyshown aquifer (Faithandothers,2010).Theyellowboxesrepresentthewellsused toconstructthe Figure 6. contacts andfaults areshownasgrayandblack lines,respectively. western flankoftheHuntonanticline (Smithandothers,2011).Previously mappedgeologic 3807500 3810000 3812500 3815000 3817500 3820000 NAD83/UTM zone 14N zone NAD83/UTM 682500 682500 Basement rocks andArbuckle Hills Timbered Groups Simpson Group rocks Post-Simpson

A perspectiveviewofthe3-DgeologicframeworkmodelArbuckle-Simpson Apparent resistivitymapfromthe helicopterelectromagneticsurveyonthesouth- 800687500 685000 685000 EXPLANATION 687500 0 0 Apparent Resistivity @ 6,200 Hz @6,200 Resistivity Apparent 690000 Arbuckle-Simpson Project Arbuckle-Simpson 690000 5,000 2,500 HEM Survey HEM 950695000 692500 950695000 692500 10,000 FEET 5,000 METERS 697500 697500

700000 700000

3807500 3810000 3812500 3815000 3817500 3820000 1447.2 1120.1 734.2 908.9 146.4 274.9 608.1 487.2 219.2 181.5 115.5 371.1 44.0 33.3 82.3 93.6 40.6 58.8 26.3 62.9 29.9 54.7 13.4 74.5 23.1 10.9 15.2 20.1 67.8 37.0 51.0 47.6 12.1 17.4 Resistivity 4.0 8.4 6.2 9.7 Apparent (ohm-m) 1

Arbuckle-Simpson 3-D Geologic Framework Model 3 to Groundwater Flow Model 96°50' 96°55' The boundary of the 3-D EV model 96°45' 1,150 1,150 of the eastern Arbuckle-Simpson aquifer 1,100 1,150 (fig.4 6) precisely matches the MODFLOW 1,100 96°40' 1,050 Acknowledgments EXPLANATION model developed by the USGS as part of 1,150 1,150 Geologic unit 1,100 the Arbuckle-Simpson Study, 1,150 1,100 1,050 Many thanks to Linda Jacobsen, Arbuckle and Timbered Hills Groups subcrop 34°35' 1,050 which was led by the Oklahoma Water 950 Eugene Schweig, Stan Paxton, and Arbuckle and Timbered Hills Groups outcrop 1,000 96°35' 1,000 1,200 Resources Board and the USGS Oklahoma 1,000 Tom Judkins who improved this 1,100 Thickness contour—Interval is 50 meters 1,150 2 950 Water Science Center. Hydrostratigraphic 1,050 Fault, exposed or inferred from 1,100 1,100 Fact Sheet with thorough reviews. published maps 1,0001,000 surfaces in EarthVision were sampled 950 900 950 1,100 1,200 Fault, inferred from subsurface geologic and interpolated to match nodes in the Jacobsen, L.J., Glynn, P.D., Phelps, G.A., Orndorff, R.C., data and concealed by younger References Cited 34°30' 1,150 1,100 MODFLOW model. These nodes provide geologic units 1,150 1,050 Bawden, G.W., and Grauch, V.J.S., 2011, Chapter 1,050 the land-surface elevations and the thick- MODFLOW model boundary 1,150 1,050 1,150 Blome, C.D., Faith, J.R., Collins, E.W., Pedraza, 13: U.S. Geological Survey―A synopsis of three- 5 1,1501,200 1,100 dimensional modeling, in Berg, R.C., Mathers, S.J., nesses of the Arbuckle and Timbered Hills 1,100 1,000 1,150 D.E., and Murray, Kyle, 2004, Geologic map 1,100 1,050 1,100 1,050 1,150 1,150 Kessler, Holgar, and Keefer, D.A., eds., Synopsis Groups,1 Simpson Group, and the post- 1,050 1,000900 compilation of the Upper Seco Creek area, 1,600 800 1,200 of current three-dimensional geologic mapping and 850 1,150 1,100 1,150 Simpson units across the entire MODFLOW 700 750 Medina and Uvalde Counties, south-central 600 650 1,300 500 1,150 modeling in geological survey organizations: Illinois 1,350 550 1,050 1,150 1,250 Texas: U.S. Geological Survey Open-File model domain. The Arbuckle and Timbered Figure 8. Thickness of the Arbuckle and 1,250 950950 900 1,350 1,500 1,050 950 1,450 State Geological Survey Circular 578, p. 69‒79. 34°25' 750 Report 2004–1430, map with pamphlet, 21 p., 850 550 650 750 850 1,000950 Hills Groups make up the major part of the Timbered Hills Groups, and faults modeled by 600 800 Johnson, K.S., 1990, Geologic map of sections of 700 750 900 scale 1:50,000. 800 650 aquifer for thickness, outcrop extent, and the 3-D EarthVision geologic framework model 750 the Arbuckle Mountains, Oklahoma: Oklahoma 700 550 750 500 450 Blome, C.D., Faith, J.R., and Ozuna, G.B., volume3 of groundwater (fig. 8). (Christenson and others, 2011). 700 600 450 Geological Survey Circular 91, plate 1, accessed 03 6 9 12 KILOMETERS 500 650 400 2006, Geohydrologic framework of the 550600 September 14, 2012, at http://www.ogs.ou.edu/ 500 Geology modified from 450 350 Edwards and Trinity aquifers, south- 0 3 6 9 12 MILES 200 Faith and others (2010) pubsscanned/CircularsPlates/C91P1.pdf. central Texas: U.S. Geological Survey Fact Pantea, M.P., and Cole, J.C., 2004, Three-dimensional Sheet 2006–3145, 6 p. geologic framework modeling of faulted hydro- Arbuckle-Simpson MODFLOW Model Cederstrand, J.R., 1996, Digital geologic map of stratigraphic units within the Edwards Aquifer, 4 Ardmore-Sherman quadrangles, south-central northern Bexar County, Texas: U.S. Geological Oklahoma: U.S. Geological Survey Open-File Survey Scientific Investigations Report 2004–5226, 96°50' A MODFLOW groundwater-flow 96°55' Report 96–370, scale 1:250,000 (available at: CD with 17-p. report. " 96°45' "" http://ok.water.usgs.gov/gis/geology). Pantea, M.P., Cole, J.C., Smith, B.D., Faith, J.R., """"""" """" " model was specifically developed to " " " "" " " """ """ " " " " " Christenson, Scott, Osborn, N.I., Neel, C.R., Blome, C.D., and Smith, D.V., 2008, Three-dimen- " " " " " " simulate discharge to streams and springs "" " " " 2 " " Faith, J.R., Blome, C.D., Puckette, James, sional geologic model of complex fault structures """"" " " " """""" " " """" " 96°40' " " " "" in the eastern Arbuckle-Simpson aqui- " " """" """" EXPLANATION " " " in the Upper Seco Creek area, Medina and Uvalde """ " "" " and Pantea, M.P., 2011, Hydrogeology "" "" "" 1,000 """ """ """ "" " " "" " 1,180 " 1,020 fer (Christenson and others, 2011). Six Geologic unit " Counties, south-central Texas: U.S. Geological " 1,040 and simulation of groundwater flow in " 1,040 " " 1,160 " Post-Simpson groups undifferentiated, " 1,060 Survey Scientific Investigations Report 2008–5131, layers of 200-meter cells were used to 1,160 " the Arbuckle-Simpson aquifer, south- " " known or inferred to overlie freshwater " " 1,040 "" "" CD with 9-p. pamphlet. 34°35' " """ 96°35' central Oklahoma: U.S. Geological Survey represent the aquifer over a total area of "" "" in the Arbuckle-Simpson aquifer " "" " "" " " " " " """" """ " " " " " "" "" " " " " 920 Smith, B.D., Smith, D.V., Hill, P.L., and Labson, V.F., "" "" " " " " 1,000 "" "" """" " " " Scientific Investigations Report 2011–5029, 1,0025 square kilometers. The resulting Simpson Group "" "" "" " " "" " " "" 1,140 " "" " "" " "" "" "" "" """""" " " 1,120 " " " " "" "" " " " " " 2003, Helicopter electromagnetic and magnetic sur- " "" " " " "" " " "" " " " "" 104 p. """ " " " "" 980 860 simulated potentiometric map (fig. 9) " " " " "" Arbuckle and Timbered Hills Groups " 1,020 " " " """ "" " "" " " "" " "" " vey data and maps, Seco Creek area, Medina and " """" " " "" "" " 1,080 Rock"" Creek " " "" "" "" " Faith, J.R., Blome, C.D., Pantea, M.P., Puckette, """" " " " "" " " "" " " " " " "" "" " " " "" " " represents over 25,000 data points and 920 " 1,000 " """" "" "" " "" " "" " " Uvalde Counties, Texas: U.S. Geological Survey " "" " """ """" " "" " " Potentiometric contour—Shows altitude "" " " " "" " " " "" "" " " "" "" 1,020 " """" "" " " " "" " """" 920 " J.D., Halihan, Todd, Osborn, Noel, Christenson, 1,060 "" "" " 1,080 "" " " """ " at which water level would stand """" "" " "" " agrees well with water level measurements "" """""" " " " 960 " " " Open-File Report 03–226, 53 p., 1 pl. " " " " " """ " " " " " 1,060 " " "980 " " " " " " 860 Scott, Pack, Skip, 2010, Three-dimensional in tightly cased well. Contour interval " " " "" "" " "" " " " " "" " " "" " "" " " "" " " """ Smith, B.D., Smith, D.V., Deszcz-Pan, Maryla, Blome, made in the field. Because of concerns that " " " "" " "" " " " """"" " " " " 20 feet. Vertical datum is NAVD 88 " """ " " "" " " " 920920 """ geologic model of the Arbuckle-Simpson 1,040 900 " " " P 1,140 "" "" " " " " " T v"ertin " " " "" " "" """ra " e " " "" " C.D., and Hill, Patricia, 2011, Helicopter electromag- """ " " " " e " " " "" " """ " " " " " " large-scale withdrawals of water from the "" "" " n """ " " " " aquifer, south-central Oklahoma: U.S. Geologi- MODFLOW model boundary 34°30' """ C "" " "" " " " " "" 940 "" " n "" " " " re "" " """"" " " 1,040 "" " " 880 netic and magnetic data, Hunton "" ek "" " i " "" " "" " "" """""" "" "" " "" " " "" 1,0001,000 " " aquifer would cause decreased streamflow, 97°00' " "" """ n "" "" " " cal Survey Open-File Report 2010–1123, "" "" " " " "" " "" " 940 Model drain cell "" "" " " g " "" "" " 920 """ " """" " "" "" " anticline, south-central Oklahoma: U.S. Geological " " "" ""t "" " " """ "" " """ " " """ ""o " "" "" " " """ "" " " "" " " 940 29 p. the model was optimized to simulate the n 980 """ "" " " " " " Drainage """ "" " 1,100 " " " " Survey Open-File Report 2011–1240, 15 p. """ "" " " " " " """ ""C " " " " " " "" "" " " " " " "" "" " " "" Blue " " 920 " effects on the streams with the largest "" " r " " " "" " " " "" " " " """" "" "" " " "" " "" " " e " " " """"""""""" " " " 880 " "" " " " " """" "" " " " """" " "" " e " " """ "" " " "" " k " " " "" """ 880 " 1,040 " """"" " " " "" 960 " streamflows: Blue and Pennington " " " " " "" 800" 920 " " " " " "" River " " " " " " "" " """ " " " "" "" " 900 By Charles D. Blome and David V. Smith " " """" " 1,060 " " """ " " 1,060 " " """ " " " "" " " " 1,040 " " "" " """""" " " 940 Creek. Model simulations of the effects of """" " "" " " " "" " " " " "" " "" " " " 820 "" " " "" " " " "" """" " "" "" " 900 " "" "" "" " " " " "" "" " " " distributed withdrawals on daily stream- " " "" " " " 840 " Contacts: " "" " " " " " 1,040" "" " " "" " " " 1,080 " "" " "" "" " " " " "" " "" " """""" " " "" " "" " " " 940 " " " " " "" Charles D. Blome David V. Smith flow show that increasing withdrawal of 34°25' " 1,060 """"" " "" "" " "" """" " "" " "" "" " " 820 " " " 1,020 "" "920 1,020" """ " U.S. Geological Survey U.S. Geological Survey groundwater from the aquifer would result " "" " " " """ """"" 940 " 780 """ " " """ " " """ " " Figure 9. Simulated steady-state """ " " MS 980, Box 25046, DFC MS 964, Box 25046, DFC """ " in reduced streamflow and in reduced """ 960 " "" " "" " " Denver, CO 80225 Denver, CO 80225 potentiometric surface in MODFLOW layer 1 " " " "" 960 "" "" discharge to streams and springs in 0 3 6 9 12 KILOMETERS """920 " """"" " " " """ [email protected] [email protected] "" " of the Hunton anticline area (modified from 900"" "" "" many locations. "" " Christenson and others, 2011). " Geology modified from Cederstrand (1996) 0 3 6 9 12 MILES This fact sheet is available online at http://pubs.usgs.gov

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