Influence of mineral ions in salt stratum on properties of cement slurry
Salt stratum,especially large thicknesses of salt stratum,are rich in inorganic salt ions such as Na+,Ca2+,Mg2+.They can enter the cement slurry through dissolution and diffusion during cementing,which will induce changes in the API performance of the cement slurry,and this is not conducive to cementing safety and quality.Taking the salt stratum drilled in a gas storage as the research object,the types and contents of mineral ions in salt stratum were analyzed by energy spectrum,and the main inorganic salt types in salt rock strata were determined.The influence of single type inorganic salt and compos-ite inorganic salt on the API performance of cementing cement slurry was evaluated by laboratory tests.The test results show that a single type of inorganic salt will cause one or more API performance of the cement slurry to fail to meet the standard re-quirements,while the composite inorganic salt will cause adverse effects on all performance indexes of the cement slurry.When the composite inorganic salt NaCl∶CaSO4∶MgCl2=42∶50∶8(mass ratio)is added to the cement slurry,the thickening time and rheological property change most significantly,in which the thickening time decreases by 55.0%,and the consistency coefficient increases by 1 260.5%.When the composite inorganic salt of NaCl∶CaSO4∶MgCl2=88∶10∶2 is added,the filtration loss and compressive strength change most significantly,in which the filtration loss increases by 58.2 mL,an increase of 158.2%,and the compressive strength loss is 9.0 MPa,a decrease of 38.3%.For salt stratum with a certain proportion of MgCl2,the cement slurry should pay attention to the optimization of thickening time,rheological parameters and compressive strength.For salt stratum with a certain proportion of CaSO4,cement slurry should strengthen the optimization of filtration.
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