Study On Weighted Oil-Based Drilling Fluid System Based On CY Oil

With the introduction of environmental regulations,the environmental requirements for oil-based drilling fluid are increasingly higher.It is very important for the development of oil-base drilling fluid to develop a more environment-friendly oil-base drilling fluid system.Based on the research and investigation of the existing base oils for oil-based drilling fluids,it is discovered that,traditionally,diesel oil,gas oil and white oil and so on were usually used as base oils in compounding oil-based drilling fluids,but they have their own advantages as well as different disadvantages.Diesel is cheap but with very serious pollution to the environments.Although gas oil has little environmental pollution,most of the gas oil is imported from abroad.There are great limitations in purchasing and transportation,and the price is extremely high.For white oil,it causes relatively less pollution to the environment and its price is reasonable,also,white oil is used as base oil in most fields,but the viscosity of white oil is relatively high,which has a certain impact on other technological parameters in the process of drilling.For the shortcomings of commonly used base oil,the environment-friendly oil for oil-based drilling fluid(CY oil)was developed in this paper by craft processes such as fractionation,hydrogenation and desulfurization with the usage of heavy hydrocarbons peculiar to Daqing.The performance of the CY oil was systematically evaluated in laboratory.The evaluation results show that the performance of the CY oil is obviously superior to other base oils such as diesel oil,which has advantages including low aromatic hydrocarbon content and little toxicity.Environmental-friendly oil-based drilling fluid system,not only the requirement for base oil is high,but also the development of high-quality emulsifier is also extremely important.Referring to the molecular structure of foreign emulsifiers,primary emulsifier and auxiliary emulsifier are synthesized independently in this paper which are suitable for oil-based drilling fluids.The major design ideas are as follows.Increasing the number or length of the oleophilic chain to improve the oleophilic capability of the emulsifier;reducing the number of branched chains to facilitate the formation of tight alignment;also,introducing positive ions to improve stability;meanwhile,introducing amide group to improve emulsifying ability while sterically protecting it;moreover,introducing tertiary amine group to improve emulsifier polarity;finally,based on the principle of similitude and affinity,the compatibility of primary and auxiliary emulsifier was improved.The synthesized emulsifiers were analyzed by infrared spectroscopy,thermogravimetric analysis,nuclear magnetic resonance test and liquid chromatography-mass spectrometry test and so on.The results showed that the synthesized emulsifiers had multiple adsorption groups which could improve the surface activity;the special molecular structure could be self-aggregated or interlap to form an interspace mesh which reinforced the compact degree and mechanical strength of interfacial film;the high temperature stability was improved by the introduced NVP monomer with five-ring structure;the emulsion droplet formed in this way is more uniform and denserat high temperature;the problems were solved effectively from traditional emulsifiers to low aromatic hydrocarbon base oil such as bad emulsifying effect and poor stability at high temperature.Based on the development of base oil and the synthesis of main and auxiliary emulsifiers,other treatment agents of oil-based drilling fluids and their amount of addition are were optimized.The formulation of oil-based drilling fluid system was determined finally as follows: 240 ml oil sample(CY oil)+ 20% calcium chloride solution + 2.5% main emulsifier(HL-TP)+ 1.0% auxiliary emulsifier(HL-DQ)+ 3% organic soil +1.5% wetting agent(DV-33)+ 6% filtrate reducer +2% shear strength-improving agent + calcium oxide + barite.According to standard experimental procedure,the rheological property,thermal stability,electrical stability,filtration property,pollution resistance,inhibition property and reservoir protection property of drilling fluid system were evaluated.The evaluation results show that the weighted oil-based drilling fluid system not only has good rheological property,but also has little change in demulsification voltage of the system after high temperature aging;the filtrate loss amounts of the oil-based weighted drilling fluid system prepared under different densities are lower,which indicates that the system has better filtration property;the weighted oil-based drilling fluid has the ability of stronger resistance to cuttings invasion and water invasion;by comparing the cuttings recovery rate and the reservoir protection performance with the diesel-based drilling fluid system and gas oil-based drilling fluid system,it is found that the compounded weighted oil-based drilling fluid system based on CY oil has the best cuttings recovery rate and the highest permeability recovery value.The results show that the system can strongly inhibit the hydration and dispersion of shale in complex strata,which can prevent wellbore collapse and effectively protect reservoir.Based on the formation of weighted oil-based drilling fluid system,the sedimentary stability of oil-based drilling fluid is primarily investigated in this paper,focusing on the relationship between barite sedimentation and viscoelasticity of oil-based drilling fluid is investigated.The effects from viscosity characteristics and elasticity of base slurry on barite sedimentation were observed by changing the addition amounts of the organic soil and the shear strength-improving agent,and it is discovered by investigation that: a.the viscoelasticity of the base mud changes with the addition amount of the organic soil.When the addition amount of the organic soil reaches a certain proportion,the growth rate of viscosity of base mud is far greater than the growth rate of elasticity.The rheological properties of drilling fluids are different with different addition amounts of the organic soil.The viscosity of base mud is bigger with more addition amount of the organic soil,when the viscosity becomes higher,the barite sedimentation becomes slower with better stability,but the shear thinning property of base mud becomes worse with the increase of viscosity.Therefore,it is not a reasonable way to reduce the sedimentation velocity of barite in base mud by changing the viscosity of base mud.b.the viscoelasticity of drilling fluids was observed by adding different amounts of shear strength-improving agent in the base mud.With the increase of addition amounts of shear strength-improving agent,the elastic modulusof base mud changes,while the viscosity increases slowly.The fluids at this time can be similar to the ones with the same viscosity and different elasticity.It can be observed from experiments that the effects on sedimentation stability of base mud are different from different elastic modulus.d.by comparing the experimental data,it can be found that both the viscosity and elasticity of the base mud have an effect on barite sedimentation,and the elastic modulus has a greater effect on barite.Through the research on base oil,emulsifier,drilling fluid system and sedimentary stability of drilling fluid,a new type of environmentally friendly drilling fluid technology is provided for deep well drilling operation with high temperature resistance,and the oil-based drilling fluid theory is enriched.