Study on Static Viscoelastic Characteristics of Drilling Fluid Using Micro-rheology

The changing process of the viscoelasticity of drilling fluid at static condition was studied using micro-rheology technology. Drilling fluids of different compositions were formulated and tested on their viscoelasticity with Rheolaser^TM after agitating at high shear speeds. Laboratory study found that it is the network formed in oil base drilling fluids that suspend barite particles. Oil base drilling fluid lost its network structure at high shear speeds and resumed the network if allowed to stand quiescent for enough time. The dissipation factor of the network, an indicator of the drilling fluid's ability to resume its original network structure, was decreasing with time, meaning that the settling speed of barite particles was becoming slower. Drilling fluids with poor behavior will lose part of their viscosity and relaxation time, leading to instability in their network structures and fast settling of barite particles. Organophilic clay and gelling agents having the ability to reinforce the micro structure of drilling fluid, when added to a certain amount, accelerate the resumption of the network in drilling fluid. Micro-rheology can be used to describe the changing process of the network formed in drilling fluid, and hence plays an important role in studying and understanding the complex performance changing of drilling fluid.