A Self-Adaptable High Pressure Bearing Plugging Agent for Synthetic-Based Drilling Fluid in Shallow Extended-Reach Well Drilling in Bohai

The direction in which the properties of the self-adaptable high pressure bearing plugging agent are specifically optimized is understood by analyzing the lost circulation scenarios occurring in shallow extended-reach well drilling in Bohai area, that is, the formations penetrated by the wells have high heterogeneity as well as pores and fractures that are randomly distributed, and lost circulation materials have to effectively plug the pores and fractures with unknown sizes to stop mud losses. The formations penetrated have microfractures that are extremely developed and low pressure bearing capacities, and lost circulation materials must have high compressive strengths. To overcome these difficulties, an oil-absorbing self-adaptable high-pressure bearing plugging agent OBR-1 was synthesized with methyl methacrylate as the backbone and other monounsaturated fatty acid esters with different of carbon chain lengths. Experimental results show that OBR-1 has high volume expansion capacity at rubbery state, high elastic modulus after absorbing oils, good broad-spectrum plugging effect and high pressure bearing capacity. Sand disks of 10-120 μm plugged by a synthetic-based emulsion containing 2%OBR-1 have pressure bearing capacity of 10 MPa. A synthetic-based drilling fluid formulated with OBR-1 as the core material can plug 20-80 mesh sand-beds with pressure bearing capacities of 20 MPa, proving that OBR-1 has excellent pressure bearing capacity and plugging performance, and can provide guarantee for the safe and efficient drilling of offshore extended-reach wells.