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In developing the Benbutu oilfield in Xinjiang, hole size irregularities were often encountered in the water- and hydrocarbon-containing sections, and these greatly affect the quality of the cementing job and damage the reservoirs. To protect the oil and gas reservoirs in the Benbutu oilfield, an elastic polymer microsphere NWL was developed through soap-free emulsion polymerization and was characterized. A reservoir protective agent CBJ was formulated with NWL, a selected anti water-block agent, a kind of rigid acid soluble nanometer particles (CaCO3) and a petroleum resin in a certain quantity ratio. Laboratory experiment was conducted to evaluate CBL in the aspects such as: the compatibility of CBL with the sizes of formation fractures, the acid solubility and oil solubility of CBL, the compatibility of CBL with the drilling fluids presently used, and the reservoir protection performance of CBL. CBL was also tested in field operations. CBL has the particle size distribution that is suitable for plugging formation fractures, good acid solubility and oil solubility. Drilling fluids treated with CBL have filtration rate reduced by about 20%, and percent permeability recovery by more than 80%. Field application and laboratory study show that CBL has good reservoir protection effect, it can be used to protect the reservoirs of Benbutu oilfield in accordance with the local conditions and maximize the production of oil wells. [ABSTRACT FROM AUTHOR]