Application Study Of Molecule Self-Assembly In Drilling Fluid Technology

The development of drilling fluid technology is often led by revolution of additives and the revolution bases on the basis of chemistry theory when additives are researched and developed.Self-assembly is the phenomenon that molecule in system aggregates and organizes into regular structure in the absence of human's intervention.Corss-fused with many subjects,self-assembly is an important source of producing new concepts,areas and technology revolutions in 21st century.Molecule self-assembly has many combinations with drilling fluid technology,which enables itself to be the basis for developing additives,achieving functions and innovating drilling fluid technology.In this paper,by combining molecule self-assembly and drilling fluid technology,we develop three additives with self-assembly feature and apply them as core additives in three focused drilling fluids.Because of its strong apolarity,it is very difficult to create networks in inverse emulsion,which causes bad rheology of oil-based drilling fluid.To overcome this problem,a polyhydroxy Gemini amphiphile(SGA)is developed.SGA is able to improve low-shear-rate-viscosity,shear-thinning performance,thixotropy,structure recovery of pure emulsion effectively at low addition,which also has syngerstic effect with organoclay.The self-assembly behavior and mechanism of rheology modification of SGA are studied based on a combine use of rheology,interface property,stability and morphology analysis.Because of the polyelectrolyte effect,regular polymer additive is unsuitable for high concentration of salt.To solve this problem,by transforming idea from salt-tolerant to salt-suitable,we develop two types of salt-responsive polymers.Research results indicate that salt-responsive polymers can assemble with salt into thermodynamically-stable dispersion,displaying absolute antipolyelectrolye effect in saturated salt concentration range.The mechanism of salt-responsiveness is studied by a combine use of rheology,turbidity,intrinsic viscosity and ~1H-NMR analysis.Salt-responsive polymers are evaluated in bentonite suspension loaded with saturated salt.Results indicate their good effect in rheology modification and fluid loss control.High-molecular-weight polyelectrolyte can form viscoelastic soliquid at low addition with excellent inhibition,encapsulation and gel-breaking performance,which enables it to use in clay-free coal bed methane(CBM)drilling fluid as suspension medium.To solve its problem of bad salt-tolerance and heat-tolerance,by introducing super-branched polycation(CPE)into soliquid of high-molecular-weight polyanion(APE),we develop self-assembly soliquid with oppositely-charged polyelectrolytes.APE-CPE soliquid is compatible with salt in essence and has good heat-tolerance.The self-assembly behavior between APE and CPE is studied by a combine use of rheology,phase behavior and morphology analysis.By using other necessary additives,three high-performance drilling fluids centering on the three developed additives are created:a high-temperature high-density organoclay-free oil base drilling fluid with upper density of 2.60 g/cm~3 and temperature of 220?;a saturated saltwater drilling fluid with upper density of 2.00 g/cm~3,temperature of 150?,excellent thermal stability and tolerance of 30%bentonite and30%shale rock cuttings;a clay-free CBM drilling fluid with good rheology,inhibition performance and low residue content.The former two types of additives and drilling fluids were applied in the field of Weiyuan shale gas block and Xinjiang oilfield,achieved good effect.