反相乳液聚合法制备改性淀粉降滤失剂及其性能

为克服水溶液自由基聚合制备改性淀粉降滤失剂存在的凝胶化问题，遵循钻井液抗高温处理剂的设计思路，采用反相乳液聚合法将淀粉与含有酰胺基/磺酸基/苯环的3种单体AM、AMPS、NVP进行接枝共聚，合成了一种新型高温抗盐抗钙降滤失剂ESt-g-NAA。首先，采用正交实验确定了反相乳液聚合的最优合成条件为:反应温度为60℃，单体物质的量比为n_NVP:n_AM:n_AMPS=1∶2∶3，亲水亲油平衡值为5。其次，对ESt-g-NAA在3%膨润土基浆中的抗高温、抗盐和抗钙降滤失效果进行了评价，结果显示:100～180℃老化16 h后，含3% ESt-g-NAA钻井液的滤失量可控制在7.6～15.2mL之间，且ESt-g-NAA钻井液的高温滤失量始终低于相同加量的水溶液聚合产物WSt-g-NAA。ESt-g-NAA显示了极强的抗盐和抗钙能力，在150℃老化16 h的饱和盐水钻井液中，滤失量仅为5 mL；含（0.5%～20%）CaCl₂的钻井液在150℃老化后滤失量控制在5.0～15.5 mL，170℃老化后可抗钙10%，但180℃老化后抗钙性能大大降低。最后，通过分析ESt-g-NAA对基浆中黏土粒度分布的影响，以及泥饼的显微观察，揭示了ESt-g-NAA的控制滤失机理。 

The Development of a Modified Starch through Inverse Phase Emulsion Copolymerization and its Performance as a Filter Loss Reducer

To overcome the gelling problem encountered in synthesizing modified starch filter loss reducer through aqueous free-radical polymerization, inverse emulsion polymerization was used to graph copolymerize starch with AM, AMPS and NVP whose molecules contain amide group, sulfonic acid group and benzene ring, respectively. The product of the copolymerization is a new filter loss reducer ESt-g-NAA with high temperature and salt and calcium resistance. The optimum synthetic conditions of the ESt-g-NAA were determined through orthogonal test: reaction temperature 60 ℃, molar ratio of the monomers n_NVP∶n_AM∶n_AMPS= 1∶2 ∶3, and the HLB value = 5. A 3% bentonite base mud treated with 3% ESt-g-NAA had filter loss between 7.6-15.2 mL after being aged at 100-180 ℃ for 16 h, the high temperature filter loss of the ESt-g-NAA treated mud was always less than the high temperature filter loss of the WSt-g-NAA (an aqueous polymerization product) treated mud with the concentrations of ESt-g-NAA and WSt-g-NAA in the base mud being the same. The ESt-g-NAA in the experiments showed excellent salt and calcium resistant capacities; a saturated salt water drilling fluid treated with ESt-g-NAA had filter loss of only 5 mL after being aged at 150 ℃ for 16 h. A drilling fluid containing 0.5%-20% CaCl₂ had filter loss between 5.0-15.5 mL after being aged at 150 ℃. If aged at 170 ℃, the drilling fluid was able to resist the contamination by 10% CaCl₂; aging at 180 ℃ greatly impaired the calcium resistance of the drilling fluid. The filtration control mechanisms of ESt-g-NAA were revealed by analyzing the effects of ESt-g-NAA on the size distribution of the clay particles in the base mud and by observing the mud cakes under microscope.