Study On Design,Synthesis And Application Of Polymers For Oil-Based Drilling Fluid

With the increase of people’s demand for energy and depletion of conventional oil and gas resevoirs,the exploration and development of oil and gas resources in unconventional reservoirs aroused widespread attention.China’s conventional oil and gas reserves are poor.And with the development of economy,the degree of dependence on foreign crude oil is increasing year by year.The exploration and development of unconventional reservoir drilling technology is crucial to ensure China’s energy security.Drilling fluids are key circulating fluid in drilling operation,which plays a role in cooling and lubricating drilling tools,transporting drilling cutting and maintaining wellbore stability.Oil-based drilling fluids are more suitable for complex drilling conditions such as geothermal wells and hydrated formations due to their better lubricity,high temperature resistance and clay inhibition.The quality of oil-based drilling fluids can be measured by its key properties such as emulsion stability,rheology and fluid loss.In practical applications,key additives are used to adjust drilling fluid properties to obtain high quality oil-based drilling fluids.However,the lack of high-performance additives for oil-based drilling fluids,such as high-temperature-resistant emulsifier and fluid-loss controller,limits the wide application of oil-based drilling fluid in complex drilling conditions.The addition of a large number of colloidal materials such as organoclay and oxidized asphalt in conventional oil-based drilling fluids are not conductive to improvement of revolving speed during drilling.The development of high quality oil-based drilling fluid requires the research of high performance additives and the construction of clay-free oil-based drilling fluids.In this thesis,we research the influence of drilling fluid additives on the performance of drilling fluids in chapter 1.Based on theme of improving the performance of oil-based drilling fluid,we designed and synthesized high-temperature resistant emulsifier,fluid-loss-control agent and viscosity-increasing polymer.Then we used them as key additives to build clay-free drilling fluids.And a selective oil absorbing material was prepared,which has application potential in oil purification and recovery of waste oil-based drilling fluid.The main content includes the following four parts:1.In order to solve the problem of emulsion stability of oil-based drilling fluids at high temperature and the difficulty of abandoned waste oil-based drilling fluids,a high-temperature-resistant emulsifier with pH response to demulsification was designed and synthesized.The emulsifier was synthesized by modifying poly(maleic anhydride-alt-1octadecene)with N,N-dimethylethylenediamine(DMEDA).The structure and molecular weight of emulsifiers were characterized by FT-IR,1H NMR,elemental analyses and multi-angle scattering.The effects of the proportion of DMEDA on the interfacial activity,pH-response and the stability of the emulsion were studied in this part.This emulsion prepared by this emulsifier can withstand high temperature aging up to 232℃.At the same time,because of the responsiveness of the pH value of the tertiary amine,the preparation of water-in-oil emulsion in neutral and alkaline conditions formed stable water-in-oil emulsion.Under acid condition,the emulsion separated apart.It provided convenience for the post-disposal of the oil-based drilling fluids prepared by this emulsifier.During evaluation of the emulsifier in oil-based drilling fluids,systems performed good rheological properties and low filtrate.These properties make the emulsifier a great application potential in high-temperature oil-based drilling fluids.2.To solve the problem of fluid loss in high-density oil-based drilling fluids at high temperature and high pressure,the amphiphilic polymer powder was prepared by amine cross-linked poly(maleic anhydride-alt-l-octadecene)as fluid-loss controller.The structure and thermal stability of the polymer were characterized by FT-IR,elemental analyses and thermogravimetric analyses.And the effects of amines on the amphipathy and fluid-loss-control performance were studied.The fluid-loss-control agent reduces the filtrate by assisting in the construction of a compact filter cake.During evaluation of the fluid-loss-control agent in oil-based drilling fluids at 176℃ and 3.5 MPa after aging for 16 hours at 232℃,the filtrate was reduced by 90%compared with a blank oil-based drilling fluid.The optimized fluid-loss-control agent has been pilot-scale production and used in oil-based drilling fluid with a filtrate reduction of more than 80%,showing potential for industrial production and application.3.Through the cross-link of poly(maleicanhydride-alt-l-octadecene)with amino-ends dimethylsiloxane,we make the viscosity of oil-based drilling fluid increasing.This method utilized the cross-linking behavior of polymer to improve the rheological properties and the ability of the drilling fluid to transport and suspend weighting materials.The influence of poly(maleicanhydride-alt-1-octadecene),amino-ends dimethylsiloxane and emulsifier on the viscosity of the system was studied by controlled experiment and the cross-linking ratio of the polymer was determined.The yield point of this oil-based drilling fluid can reach 6.5 Pa after hot rolling.It is found that the sedimentation rate of barite slows down and the demulsification voltage of the oil-based drilling fluid increased with polymer added,indicating that the suspension stability and emulsion stability of drilling fluid are enhanced.This way of cross-linking polymers in drilling fluid provides a new idea for rheological adjustment of oil-based drilling fluids and lays a foundation for the construction of clay-free oil-based drilling fluids.4.Polymer microspheres with particle size of 300-400 nm were prepared by the soap-free emulsion polymerization of styrene,2-ethylhexyl acrylate and divinybenzene oleophilic monomers.The structure and stability of polymer microspheres were characterized by FT-IR spectra,elemental analyses and thermogravimetric analyses.And the particle size distribution was determined by scanning electron microscopy,transmission electron microscopy and dynamic light scattering.The microspheres were used to enhance the suspension of weighted materials in oil-based drilling fluids.Performance evaluation results show that the synthesized polymer microspheres make the viscosity of water-in-oil emulsion increasing and improve the suspension stability of the drilling fluids weighted with barite.On this basis,the clay-free oil-based drilling fluid was constructed by using the emulsifier synthesized in chapter 2 and the cross-linking polymer in chapter 4.The drilling fluid performance evaluation experiment shows that the system has high demulsification voltage,good rheological properties and low filtrate,which make this drilling fluid have the potential of industrial application.5.The feasibility of preparing hydrophobic materials using poly(maleicanhydride-alt-1-octadecene)(PMAO)as a modifier of polydopamine coating was verified on the substrate of silica nanoparticles.Then,a superhydrophobic sponge with large adsorption capacity,good oil-absorption selectivity and tolerance to extreme conditions was prepared by using the same reaction condition to modify melamine sponge.Due to the micro-nano rough morphology by self-polymerization of dopamine on the substrate,the hydrophobicity of sponge is improved,which make modified melamine sponge have good selectively adsorption ability and recyclability.These characteristics make this material have the application value of selective recovery of oil from oil-water mixtures and abandoned oil-based drilling fluids.