Apparatus for the optimization of the rheological characteristics of viscous fluids

An apparatus for optimizing the rheological properties of a viscous fluid, comprising:

• a housing for connection in the flow path from a subsurface reservoir to the surface, the housing having a first through bore defining a cross-sectional flow area and a longitudinal flow path for fluid through the bore;
• the through bore having an inlet end for connection to a supply of a viscous fluid in a subsurface reservoir and an outlet end;
• a flow restriction device in the through bore defining a reduced area orifice for restricted flow;
• an adjustment device for varying the size of the orifice:
• and
• at least one magnetic assembly for selective connection to one end of the housing, the assembly having a second through bore for communicating with said first through bore in the housing, and a magnetic field source for generating a magnetic field across at least part of the second through bore in a direction transverse to the fluid flow path.