Environmentally-friendly sealed coring technology for unconsolidated formations

After long-term waterflooding development, the high-porosity, high-permeability unconsolidated sandstone oil reservoirs with the Gangxi Oilfield and Gangdong Oilfield of Dagang Oilfield as the typical ones suffer serious invasion of formation water, so the traditional sealed coring technologies for unconsolidated formations can hardly ensure the core recovery and sealing rate. To solve the low operation efficiency, environment pollution and other problems of traditional sealed coring technologies, the inner cylinder assembly was optimally designed based on the geological characteristics and coring technical difficulties of Minghuazhen Formation and Guantao Formation in the Dagang Oilfield. The low-erosion coring bit was adopted to deal with the low core recovery and complex coring process of watered-out unconsolidated sandstone formation. The low-toxicity environmental chlorinated paraffin based sealing fluid was prepared by improving the sealing fluid processing process. And the safe and environmental sealing fluid treatment process was formed by using the water-bath sealing fluid heating method and the sealing fluid retrieving device. The successful overall sealed coring in two wells indicates that the adoption of scientific and rational technologies and measures can effectively improve the operation efficiency and coring quality of sealed coring and satisfy the safety and environment requirements of coring operation and drilling site.