Research On Calcium Carbonate Nanoparticles For Water-based Drilling Fluids

With the rapid development of society and economy,the demand for energy increases quickly.The problem of energy shortage has attracted attentions of many researchers.Therefore,the demand for unconventional energy sources such as shale gas and low-permeability reservoirs has received more and more attention.The shale gas reservoir has the characteristics of high clay content,large number of cracks and easy hydration and expansion,which makes the drilling wellbore unstable.There are a large number of small pores in the shale formation,and the permeability of the fluid leads to decrease in reservoir stability.In the process of drilling opreations,the effective plugging of water-based drilling fluids in the micropores of the reservoir is one of the important measures to ensure the stability of the wellbore.Combining nanotechnology with drilling fluid system,the development of nanomaterials for water-based drilling fluid is an important route for efficient and safe development of shale gas.In this paper,a series of calcium carbonate(CaCO3)particles and polymer surface modified CaCO3 nanoparticles were prepared to meet the needs of water-based drilling fluids for the exploitation of shale gas.The effects of CaCO3 particles on the rheological properties and plugging properties of water-based drilling fluids were investigated.The modification of the polymer can control the size of the CaCO3 particles.Moreover,the dispersibility of the nanoparticles were enhanced by the electrostatic repulsion and steric repulsion provided by the polymer,and the surface modification was used to impart special surface functions to the nanoparticles for improving the rheological properties and plugging properties of the water-based drilling fluid.The main research contents are as follows.(1)CaCO3 particles were prepared through metathesis reaction and used as waterbased drilling fluid treatment agents.The morphology and composition of CaCO3 particles were characterized and their effects on the performance of drilling fluids were investigated.The experimental results showed that the rheological properties of waterbased drilling fluids were affected lessly by the CaCO3 particles compared to the original drilling fluid.With the increase of the CaCO3 particles,the fluid loss volume of the water-based drilling fluid decreases and then increases,and the minimum fluid loss volume was obtained at a concentration of 0.1 wt%.Based on the micromorphology of the filter cake,CaCO3 micron particles are dispersed in the mud cake,but it is difficult to effectively block the micro-nano pores due to its large size,resulting in a large fluid loss.(2)Polyacrylic acid(PAA)modified CaCO3 nanoparticles(CaCO3/PAA)were prepared by in-situ radical polymerization.The products were characterized by infrared spectroscopy,scanning electron microscopy,thermogravimetric test and zeta potential.The obtained CaCO3/PAA nanoparticles were used as additives to modify the rheological and filtration properties of water-based drilling fluids.The results show that the viscosity of water-based drilling fluids at low shear rates was improved with the addition of 0.05-0.1 wt%CaCO3/PAA nanoparticles,resulting in superior shear thinning performance.The yield point of the water-based drilling fluid was increased from 0.18 Pa to 0.43 Pa due to the addition of 0.1 wt%nanoparticles.And the gel strength of drilling fluid system was also increased.At the same time,the fluid loss volume of drilling fluid was reduced with the addition of nanoparticles,and the minimum fluid loss volume was achieved at a concentration of 0.1 wt%.The fluid loss volume was reduced by 10.4%at 25? and the filtration performance and the filter cake quality were improved.Photographs of the microscopic morphology of the filter cake showed that the micro-nano pores between the bentonite sheets were blocked by the CaCO3/PAA nanoparticles to prevent water passing through and the filtration was decreased.(3)Anionic polyacrylamide surface modified CaCO3 nanoparticles(CaCO3/APAM)were prepared by in-situ free radical polymerization,and as a waterbased drilling fluid nano-treatment agent.The effects of CaCO3/APAM on performance of water-based drilling fluid were investigated.The results show that the viscosity of the system at low shear rate was improved and the shear thinning performance was significantly enhanced with the addition of CaCO3/APAM nanoparticles.In addition to the normal temperature conditions,the performance of the drilling fluid under high temperature conditions was also tested.When the fluids were tested at 80?,the rheological behavior of the modified water-based drilling fluid was consistent with the Herschel-Bulkley fluid model,and the addition of CaCO3/APAM decreases the flow index n significantly.The results of the fluid loss experiment showed that the fluid loss volume decreased with the increase of the concentration of nanoparticles,and the optimal concentration was 1 wt%.The fluid loss volume reduced from 32.5 mL to 24.6 mL at 110?,reducing by 24.3%.Salt-tolerant fluid loss experiments showed that the fluid loss volume of water-based drilling fluids was significantly reduced with the addition of nanoparticles,demonstrating that the nanoparticles are effective plugging agents in salt-containing water-based drilling fluids.(4)Poly(2-acrylamido-2-methylpropanesulfonic acid(PAMPS)modified calcium carbonate nanoparticles(CaCO3/PAMPS)were prepared by in situ radical polymerization and added to water-based drilling fluid to modify the performance.The rheological test showed that the shear thinning performance of drilling fluid increased with the addition of CaCO3/PAMPS nanoparticles.When the concentration was 1 wt%,the shear thinning performance at 80? was significantly enhanced.The drilling fluid filtration test showed that the fluid loss volume was effectively reduced in the presence of nanoparticles.When the amount of nanoparticles was 1 wt%,the minimum filtration loss and the lowest filtration loss rate were obtained.The microscopic morphology of the filter cake showed that the blocking of the micropores of the nanoparticles in the filter cake formed a denser filter cake,which improves the plugging performance.In conclusion,calcium carbonate particles for water-based drilling fluids were studied in this work.CaCO3 micron particles,CaCO3/PAA,CaCO3/APAM and CaCO3/PAMPS nanoparticles were prepared to modify the performance of water-based drilling fluids.The experimental results showed that CaCO3 micron particles can not effectively improve the performance of water-based drilling fluid.While the rheological properties,plugging performance,and temperature and salt tolerance of water-based drilling fluids were effectively improved with the adding of the polymer surface modified calcium carbonate nanoparticles.