A novel self-generating nitrogen foamed cement: The preparation, evaluation and field application

Insufficient top of cement due to lost circulation is an urgent and worldwide technical challenge for oil and gas well cementing. Foamed cement (FC), especially the nitrogen FC, is a promising technology to prevent cement loss occurring in formations with low pressure, naturally occurring fractures or high permeability. However, the existing technology for nitrogen FC is either mechanically complicated or chemically low efficiency. This paper introduces a chemically self-generating nitrogen foamed cement (SNFC) with high performance to meet the requirements of oil and gas well cementing. Based on chemical thermodynamics and electrochemistry, a new nitrogen gas generating reactant (NGR) with high gas generation efficiency has been developed. The mixture of four surfactants with optimized mass ratio is used as the foam-stabilizer. The nitrogen FC is prepared by the injecting and mixing method in a closed vessel. Extensive laboratory tests were conducted to evaluate the properties of this SNFC, such as fluidity, free water, API fluid loss, thickening time, density and compressive strength. Experimental results indicate that the density of SNFC slurries can be adjusted from 1.25 to 1.60 g/cm3, and the SNFC stone has high compressive strength and low gas permeability. This kind of nitrogen FC has been successfully applied in cementing low-pressure formations.