Research And Application Of Low-injection Clearing Liquid For Tight Reservoir Nitrogen Drilling

Nitrogen drilling in the case of heavy oil reservoir,oil will cause the debris to form a large size viscoplastic rock mass,cause well bore cleaning difference,ring air blocking or card drilling and other downhole complex,at present,the prevention and treatment technology of nitrogen drilling in the oil is not improved,as to restrict the promotion and application of nitrogen drilling in heavy oil reservoir.To this end,this paper takes the effect of formation oil on nitrogen drilling as the starting point,based on the reservoir protection technology,the research on the system of low damage sand cleaning liquid for nitrogen drilling in tight reservoir is carried out.Study on heavy oil properties and components,and from the physical and chemical properties and rheological properties of heavy oil and other aspects of the cluster analysis, pointed out that high viscosity is the result of ring air core oil droplet size,oil is difficult to carry to the ground,causing the main reason for the ring air blockage and other accidents.So the key to clean sand is to reduce the viscosity of heavy oil.Studying on physical viscosity reduction(heating viscosity reduction,mixing thin oil viscosity reduction,ultrasonic viscosity reduction)method and chemical viscosity reduction(emulsifying viscosity reduction, oil-solubility viscosity reducer viscosity reduction)method,comprehensive comparison of its advantages and disadvantages,combined with the actual situation of the site selected emulsification and viscosity reduction.By orthogonal test,timing area method,wafer canvas method,rolling recovery rate experiment,experiments of the grain-size analysis and high temperature and high pressure plugging experiment etc.method of clear sand base fluid,reducing adhesion agent,penetrating agent and plugging agent were optimized,were constructed with active water,water in oil emulsion,oil in water emulsion as base solution of three kinds of sand cleaning fluid system, and finally select the active water cleaning sand liquid,formula is:active water+0.2%viscosity reducing auxiliary agent+2%penetrating agent+1.5%plugging agent.Adhesion and aggregation test,static dissolution test,combined with three-dimensional reconstruction image of X-CT,study on the performance of cleaning sand from the macro and micro perspectives, results show that the active water cleaning sand liquid can effectively remove the clay and oil mixture adsorbed on the steel bar.Oil sand mud loose structure after dissolution,surface produced a large number of mesh cracks,obvious holes and cracks can be observed in the three-dimensional reconstruction image of X-CT.Active water sand cleaning liquid bear temperature up to 120?,the higher the temperature,the sand cleaning fluid damage breaking sludge group more thoroughly.When the degree of mineralization is lower than 15000mg/L, the viscosity reduction effect is good.In addition,the active water sand cleaning liquid also has a very good reservoir protection effect, permeability recovery value above 90%,less damage to the formation.