Aberrant gelation mechanism initiated by component difference of oil well cement slurry at high temperature and its regulators

The aberrant gelation behavior of oil well cement (OWC) slurry in the high-temperature and high-pressure environment (usually occurs between 100-150 ℃) would block the wellbore and endanger its pumping security. Herein, the aberrant gelation mechanism caused by the mineral component differentiation of OWC slurry was studied. Results indicated that the relative content of gypsum and tricalcium aluminate (C3A) was unbalanced for the OWCs that were prone to aberrant gelation (Gypsum/C3A<1). This ratio tended to induce premature hydration of aluminate minerals and a small portion of tricalcium silicate (C3S). As a result, more C3S and the hydration product monosulfoaluminate (AFm) of C3A migrated towards the gelatinous zone. Furthermore, the increased dosage and fineness of quartz sand (QS) would expand its relative proportion in the gelatinous zone and aggravate the aberrant gelation degree of the OWC slurry. Driven by the over-strong pozzolanic reaction, high dosage or high fineness QS tended to adsorb onto the surface of cement minerals that were hydrating to produce calcium hydroxide (CH), and then migrate together with the cement minerals to the gelatinous zone and aggravate the aberrant gelation degree. Therefore, in order to minimize the impact of QS on aberrant gelation behavior, the optimal utilization scheme of QS was to minimize its dosage and mesh number as much as possible under the premise of ensuring normal compressive strength development. Based on the mechanism study, two anti-aberrant gelation regulators (gypsum and sodium hydrogen sulfite, SHS) were discovered. Proper dosages of gypsum (0.5 - 2.0% bwoc) and SHS (0.1 - 0.3% bwoc) could significantly relieve the aberrant gelation by simultaneously delaying the premature hydration of C3A and part of C3S in the cement minerals.