Abstract
In deepwater drilling, aqueous drilling fluid (ADF) is meaningful because it could be a potential alternative to non-aqueous drilling fluid (NADF). However, its rheological properties varies notably over a broad range of temperature, driving technical hazards including equivalent circulating densities control and lost circulation. Reducing the temperature dependence of the rheololgical properties of ADF thus is a crucial step towards achieving successful and cost-effective deepwater drilling operation. Herein, the combination of clay particles and new class of thermo-associating copolymer, CGBA which was reported in our previous works was exploited to conquer this issue due to their distinct inherent properties. In detail, the contribution of CGBA in driving viscosity enhancement macroscopically in aqueous solution and slurry across a temperature range of 4–170℃was preliminary evaluated by viscosity measurement, zeta potential measurement, and differential scanning calorimetry (DSC). Results from rheological test indicated that, CGBA showed remarkable thermo-thickening phenomenon in slurry ascribed to the self-assemble of BA side-arms. The absolute value of the zeta potential of CGBA aqueous solution increased in slurry. DSC experiments showed that, albeit CGBA in aqueous solution and slurry displayed similar endotherms process, both phase transition and heats of transition decreased from 62 to 43 ℃ and 2.13 to 1.71 kJ/mol DEAm, respectively in slurry. The thermo-rheological properties dependence of the aged CGBA containing drilling fluid was further examined across the temperature range of 4−75 ℃ following the American Petroleum Institute (API) procedure. Results clearly indicated that the designed FR-ADF delivers more stable rheology than those of typical ADF. The change rate of key rheological parameters of the designed FR-ADF, such as, plastic viscosity (PV), yield point (YP) and low shear rate viscosity (LSRV) were less than 30 %. Additionally, the laboratory contamination tests indicated that the designed FR-ADF was found to possess good inhibition properties as well as strong tolerance to the contamination of salts. Albeit the contamination to mudstone cuttings impacted the fluid rheology, the change rate was within an acceptable range. In comparison with reported FR-NADF, the designed FR-ADF showed great potential for application in deepwater drilling operations. This work introduces for the first time a N,N’-diethylacrylamide-based sticker as a novel rheological modifier in deepwater ADF to further broaden the established theory of thermo-associating copolymer in deepwater ADF.
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