Page 286 - Origin and Prediction of Abnormal Formation Pressures
P. 286

258                                 H.H. RIEKE, G.V. CHILINGAR AND J.O. ROBERTSON JR.

            TABLE  10-7
            Variation in the  composition  of the  supernatant  liquid  and pore  water centrifuged  out of smectite  clay (API
            No.  25,  Upton  WY,  USA);  the  chlorinity  ratios  (Ca/CI,  K/C1  and  Na/C1)  are  presented  along  with  the
            Na/C1  and Ca/Mg  ratios  (after Rieke,  1970)
            Ions        Composition,  ppm
                        seawater,  St   supernatant   centrifuged   remaining   remaining
                                    liquid,  S1   liquid,  82   liquid,  $3   liquid a, $3
                        (Vt  =  10 ml)   (V~  =  2.95  ml)   (V2  =  2.9 ml)   (~  =  4.15  ml)   (V3 =  4.15 ml)
            Ca 2+         480         444          462         518.2        431
            Mg2+         1,283        765          794        1,992         744
            K +           427         260          274         652.6        250
            Na +        10,554      13,949       14,813       5,164       13,345
            SO 2-        2,172       4,380        4,471          b         4,292
            C1-         19,574      20,355       21,823       16,202      19,329
            Total solids   34,490   40,153       42,661      24,530       38,391
            Na/C1        0.539       0.685        0.678       0.319        0.69
            Ca/C1        0.0245      0.0218       0.0212      0.0320       0.0223
            K/C1         0.0218      0.0128       0.0126      0.0403       0.0129
            Na/C1       21.9        31.4         32.0         9.966       30.96
            Ca/Mg        0.374       0.58         0.581       0.26         0.579
            a Remaining  liquid composition  was calculated using the supernatant  liquid as the starting  fluid.
            b The results are not reported because the clay tested  appears  to have a high  SO42- content.


            TABLE  10-8
            A  summary  of  the  chemical  analyses  of  the  major  cations  present  in  the  pore  water  of  the  original
            (unleached)  clay  sample  (undisturbed  marine  clay,  Drammen,  Norway)  and  the  cations  present  in  the
            leachate (after Kazi  and  Mourn,  1972, table  2, p.  10)
            Cation   Cation  concentration a   Remarks
                     pore water   leachate
            Na +     438.73     484.57      Na +  and  K +  are leached in excess  of that present in the pore
            K +       15.66      36.85      water of the original  sample,  whereas the amounts of Ca 2+
            Ca e+     21.93      16.15      and  Mg 2+  in the  leachate are lower than those in the original
            Mg 2+     41.78      26.46      sample.
            a Expressed in mg/100  g of the original dry weight  of the sample.


            the  free  pore  water,  was  removed  and  analyzed.  The  remaining  saturated  sample  was
            placed  in  a  hydrostatic  compaction  cell  (Sawabini  et  al.,  1971)  and  the  successive
            portions  of the  expelled  solutions  were  analyzed.  The  final  remaining  moisture content
            was  62%,  which  corresponds  to  an  overburden  pressure  of  35  kg/cm 2  (3.43  MPa).
            The  results  presented  in  Table  10-9  illustrate  that  the  concentration  of  the  various
            ions  expelled  at  the  initial  stages  of  compaction  are  slightly  higher  than  that  of  the
            original  pore  water  present  in  the  smectite  clay  saturated  in  seawater.  As  shown  in
            Fig.  10-17,  the concentration  of the various  anions  and cations go through a maximum,
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