High-temperature High-performance Organoclay-free Oil Based Drilling Fluid Technology Research

Traditional low-colloid oil-based muds?OBMs?use organoclay as rheology modifier.Because the dosage of organoclay is small,the yield point and yield point/plastic viscosity ratio are low,which adversely influences hole cleaning capability.Besides,the colloidal materials including organoclay,blown asphalts and organic lignites in oil muds have an adverse impact on rate of penetration?ROP?.Besides,if the dosage of these materials is high,it will substantially decrease ROP.Aiming at the above problems,an organoclay-free oil based drilling fluid system without using organoclay or any other colloidal materials was developed.Both indoor performance evaluation and field test showed that the organoclay-free oil based drilling fluid outperformed traditional oil based drilling fluids.The developed high-performance organoclay-free oil based drilling fluid is made up of four core technologies:a rheology modifier that can replace organoclay and provide a weak gel structure,a polymeric filter reducer that can control filter loss without under no organoclay environment,primary and secondary emulsifiers that provide high-temperature emulsion stability and a nanoscale plugging agent that can plug nanoscale pores during shale drilling.Firstly,this paper introduced the supramolecular chemistry theory into drilling fluid area and a small-molecular rheology modifier that can replace organoclay in oil based drilling fluid was synthesized.The rheology modifier can establish three-dimensional networks in water in oil emulsions and provide a weak gel structure.The application of the rheology modifier in an organoclay-free OBM showed that a higher yield point?YP?,higher Gel strengths and a higher electrical stability?ES?were achieved in comparison with the conventional OBMs.Secondary,high-temperature high-pressure filtration is difficult to control under the environment without oganoclay.In order to solve the problem,a styrene/butyl acrylate/acrylic acid terpolymer was synthesized as filter reducer which has an outstanding thermal stability because of its carbon-carbon single bond backbone structure.The filter reducer slightly affects system rheology and can substantially reduce API and HTHP filtrations by improving the quality of mud cakes.In comparison with most commonly used filter reducer in OBMs blown asphalts,the synthesized polymeric filter reducer exhibited better emulsion stabilizing ability,better filtration property,better plugging ability and better thermal stability.Thirdly,aiming to plugging nanoscale pores in shale formation,a shell-core structural acrylic resin/SiO₂ composite was synthesized to enhance the plugging ability of OBMs.This material can be resistant to high temperature of more than 250°C.Membrane efficiency experiments showed that the nanocomposite can significantly enhance plugging efficiency and reduce filtrate invasion into shale.Fourthly,two high-temperature emulsifiers were synthesized:primary emulsifier modified fatty acid and secondary emulsifier fatty acid amide.The electrical stability values?ES?of drilling fluids using the emulsifiers were more than 400V after aging at220?for 16h,which indicates a good thermal stability.Finally,high-temperature high-performance organoclay-free oil based drilling fluids with different densities,which can be resistant to high temperature of 220°C,were formulated using the above five key additives.In comparison with traditional OBMs,high-temperature high-performance organoclay-free oil based drilling fluids have better rheological structure and lower reservoir damage.Field test showed that the developed organoclay-free OBMs were very stable and easy to maintain.In comparison with neighboring wells,the well construction cycle for the application well section was reduced by 33%.