Measurement of the Permeability of Set Cement

Abstract

Introduction A satisfactory well-cementing composition must retain its fluidity longenough to be pumped into place; then it must develop within a reasonable lengthof time sufficient strength and impermeability to anchor the casing in positionand to form an effective seal between the casing and the formations. Theseproperties may be evaluated by pump ability, strength (compressive or tensile), and permeability tests. Laboratory test procedures for the determination of pumpability time andstrength development have been outlined previously and are readily available, but a satisfactory and convenient laboratory procedure for the measurement ofthe permeability of set cement has not been developed heretofore. Some permeability data have been obtained previously by passing air throughdried cement specimens. Such a procedure is unsatisfactory because the dryingof set cement alters its physical and chemical properties and subjects it toconditions dissimilar to well conditions. A more realistic method would be onewherein the cement remains water-saturated during the aging period and thepermeability is measured with water. Such a procedure, outlined below, has beenused by the authors for the past four years to evaluate well-cementingcompositions. Permeability Test Procedure The brass mold, shown in the upper left-hand corner of Fig. 1, is cleansedwith emery polishing paper and placed on a flat plate and the test slurry ispoured into the mold. The slurry is puddled several times with a stirring rodand levelled off with a spatula. Another flat plate is placed on top of themold to complete the enclosure before the mold is placed under water at thedesired curing temperature. After the cement slurry has aged for the desiredlength of time, the mold containing the set cement is taken from the waterbath, the cover plates are removed, and the specimen is cooled under water toroom temperature. The faces of the set cement (in the mold) are brushed under astream of water to remove the glazed surface and foreign matter. T.N. 120