Polyalkyl methacrylate copolymers for rheological modification and filtration control for ester and synthetic based drilling fluids

An oil-based fluid system for use in oil and gas drilling operations comprising:

• about 0.5 to 10 lb active material/bbl of a polyalkyl methacrylate with vinyl pyrrolidone copolymer having a weight average molecular weight from about 200,000 to about 450,000 g/mole;
• a weighting agent;
• and
• a base fluid making up the balance, where the base fluid is selected from the group consisting of:
• oil,
• invert emulsion base fluids containing an emulsifier and brine,
• esters,
• olefins, and
• paraffins;
• where the proportion of the copolymer is based on the base fluid.

A method of placing a fluid system in a well comprising:

• providing an oil-based fluid system comprising:
• a base fluid selected from the group consisting of:
• oil,
• invert emulsion base fluids containing an emulsifier and brine,
• esters,
• olefins, and
• paraffins, and
• a weighting agent;
• mixing into the fluid system a polyalkyl methacrylate with vinyl pyrrolidone copolymer;
• and
• circulating the fluid system within a bore hole in an underground formation.

A method of drilling a well comprising:

• providing an oil-based fluid system comprising:
• a base fluid selected from the group consisting of:
• oil,
• invert emulsion base fluids containing an emulsifier and brine,
• esters,
• olefins, and
• paraffins, and
• a weighting agent;
• mixing into the fluid system a polyalkyl methacrylate with vinyl pyrrolidone copolymer;
• and
• circulating the fluid system while drilling the well within a bore hole in contact with a drill bit and an underground formation.

A method of treating a well with a spotting fluid system comprising:

• providing an oil-based fluid system comprising:
• a base fluid selected from the group consisting of:
• oil,
• invert emulsion base fluids containing an emulsifier and brine,
• esters,
• olefins, and
• paraffins, and
• a weighting agent;
• mixing into the fluid system a polyalkyl methacrylate with vinyl pyrrolidone copolymer;
• and
• circulating the resulting fluid spotting fluid system within a bore hole in contact with drill pipe and an underground formation.