A Viscoelastic Surfactants: Its Development and Application in Micro Foam Drilling Fluids

A viscoelastic anionic surfactant VES-1 has been synthesized with amino-compound and long-chain acryl chloride for use in micro foam drilling fluids. A micro foam mud treated with VES-1 was formulated with selected micelle enhancer and secondary surfactants. The micro foam mud had good viscoelasticity and stable foam. Low shear rate (0.01 r/min) viscosity of the foam mud is 100 000 mPa·s, and the half-life longer than 18 min. Based on the formation characteristics of the Wen-23 gas storage, the VES-1 micro foam mud was further treated with foam stabilizer and filter loss reducers to form a micro foam mud of high thixotropy. Laboratory evaluation results have proved its high thixotropy and ability to quickly form network structure inside the mud. The initial (10 s) gel strength of the VES-1 foam mud was at least 12 Pa, and there was only slight difference between the 10 s and 10 min gel strengths. This is especially beneficial to carrying drilled cuttings out of hole and plugging low pressure thief zones to avoid mud losses. VES-1 is apparently superior to the commonly used surfactants (such as OP-10) in mud loss control under pressure. In mud loss experiment, injection of 325 mL of the VES-1 mud at 120℃ increased the pressure to above 10 MPa, indicating that this mud can help resolve mud loss problem in low pressure formations. VES-1 micro foam mud also had good pressure resistance; its density increase did not exceed 0.05 g/cm³ under 30 MPa. After aging at 120℃ for 16 h, the mud properties remained unchanged. The VES-1 mud is able to resist contamination by 10% compound saltwater. It also has good lubricity; the friction coefficient of the VES-1 mud is 54% less than commonly used polymer drilling fluids. Properties of the VES-1 micro foam mud are able to satisfy the needs for the construction of the Wen-23 gas storage.