| Abstract |
To deal with lost circulation during construction of geothermal wells, Brookhaven National Laboratory (BNL) has developed a temporary sealing material, which plugs fractures during drilling operations and opens them later by disintegration when the drilling is completed, by introducing carboxymethyl celluloses (CMC) into alkali-activated slag/fly ash cementitious material. Poly lactic acid (PLA) not only has been widely used in medical industry as additive for degradation of biocompatible bone cements, due to its biocompatibility and biodegradability; but also applied to fluid-loss control, fluid diversion, filter-cake removal in oil and shale gas fields for its degradability, in recent years. This paper aims at studying potential of PLA to further promote degradation of the temporary sealing material, by introducing PLA to the material. Thermo Gravimetric Analysis (TGA) was employed to study thermal decomposition behavior of PLA and effects of alkali-activated slag/fly ash cementitious material on it, the thermal decomposition temperature declined after PLA was treated by filtrate of the cement. Pyrolysis-Gas Chromatography/Mass Spectroscopy (Py-GC/MS) was employed to study main products derived from the thermal decomposition of PLA. And the main products, gamma-butyrolactone, o-xylene, hexyl alcohol and 3-ethyl-3-buten-2-ol are in gaseous state at about 200℃. The addition of PLA could increase the material’s fluidity, reduce specimens’ surface cracks, and generate much more pores in specimens after 200℃-heated, compared with the temporary sealing material without PLA. Compressive strength of the 85℃-cured specimens declined as content of PLA increased, it was 6.76 MPa when the content reached 5%. The preliminary conclusion is: PLA has an ability of further promoting the self-degradation of the temporary sealing material. |