Evolution of Conduits in the Edwards Group by Nk0jAc3Y

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									Complexities of the Flow System,
      Edwards Aquifer

     Susan Hovorka, Bureau of Economic Geology
                     with data from:
  Geary Schindel and Steve Johnson, Edwards Aquifer
                        Authority
        J. P Nicot, Bureau of Economic Geology
      Steve Worthington, Worthington Associates
 Adrien Lindley and Thandar Phu, University of Texas at
                         Austin
                        Purpose

• What is the scale, distribution , and hydrologic significance
  of heterogeneity in the Edwards aquifer?

• How much information can be extracted from existing
  data?

• Where are productive areas for future research to better
  answer this question?
                       Techniques
• Thin section petrography
• Measurement of porosity and permeability core plugs from cores and
  outcrops
• Calibration of wireline logs using core plug data and
  porosity/permeability transforms
• Core examination
• Fracture aperture measurement
• Outcrop photograph digitization
• Cave trend analysis
• Calculation of permeability from specific capacity tests
• Well hydrograph recession analysis
• Pseudosynoptic analysis of troughs in the water level
• Calcite saturation and other geochemical indicators
Facies Cross Section
Based on log analysis
Variation in Water Level
High Permeability Deep in the Aquifer
                              Pore Types vugs (molds)
               Intergranular pores    Separate




              Intercrystalline pores   Touching vugs




Bureau
   of
   Economic
 Geology                                                QAa4613c
Permeability in Carbonate




1 mm
Dissolution of dolomite during diagenesis
                            Randolph FM 1604 core, 924 ft
Impact of Gypsum on
   Permeability

            Calcitized gypsum =
            vuggy, zone, moderate
            to low permeability
            Conduit Flow Dominates
• To match
  springflow,
  models must
  upscale
  transmissivity
  several orders of
  magnitude above
  estimated
  transmissivity
  from wells        High transmissivity areas of Maclay and Land
                      overlain on well-test-derived permeability mode
                      SWRI, 2002
      Conduit Flow Dominates
                                     • In wells with
                                       estimated
                                       transmissivity,
                                       matrix flow
                                       accounts for
                                       about 1% of
                                       total flow.

Mace and Hovorka, permeability from core compared to
permeability calculated from specific capacity
Fractures and Caves are Obvious in Outcrop
From G. Schindel
Evolution of Karst, Confined Zone




               Hovorka and Yeh
       Karst features
        are found in
       the confined
          aquifer

        Missing section, terra rosa,
        Off-scale caliper




5 cm
                Effects of faulting on
                    permeability
                                        Fracturing focuses
                                        development of karst




                            Caves

Offset decreases cross-   Fractures and
fault transmissivity      brecciation increase
  Bureau
     of
     Economic
                          permeability parallel to
   Geology                                                     QAa850

                          the fault
Topographic Expression of
Balcones Fault Zone, Austin
Mixing Zone Dissolution –
    Matrix and Karst
t1


      t2
           t3
                t4 t5
 Tracer tests to
 define conduits
 in Barton Springs
 segment
Brian Smith BSEACD
Nico Hauwert COA
Uranine Tracer Test Results in the Landa Park Area
                                                                                #
                                                                                        #




                                                                            #




                                                               #

                                                           #




                                                                     Uranine
                                         #




                                                           U
                                                           %       NBU Well 5
        Eosine                   #
                                 #
                                                 #
                                                 Y
                                                       #

                             #
                             #


                         #
                                             #
                 #
                 #
                 #

            r


                                 #   #


    Panther Canyon   #
                                 #



    Well

                r
                             LCRA Well                                              #
                                                                                    Y




                                                     Schindel, Johnson and others, 2002
Conduit Interpretation
  (Steve Worthington)
                                     San Marcus Sp.


                                          Comal Sp.




         Base permeability from SWRI, based
         on statistical handling of well tests
Synoptic Potentiometric Surface of
     San Antonio Segment




            Esquilin, 2003 provisional synoptic
  Trough in Water Level Interpreted as
              Conduits




Brian Smith, Barton Springs Edwards Aquifer CD; Nico Hauwert City of Austin
Conduits Interpreted from
   Pseudosynoptics
Interpreted Conduits Compared to
         Other Indicators
             Conclusions

• Matrix permeability is inadequate to
  describe Edwards flow system
• Numerous lines of evidence suggest
  that conduit flow dominates

								
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