Mechanism Research On Temporary Plugging And Diversion Of Emulsified Diesel For Oilfield W In South China Sea

In the process of well production,drilling,well completion and other measures may lead to reservoir pollution and worse porosity and permeability in the near-well zone,which may lead to the aggravation of inter-layer contradictions and further affect the oil production.Acidizing is an effective measure to improve seepage condition and restore productivity after reservoir pollution.In order to achieve uniform acid distribution in the well,the acidizing technologies including mechanical equipment blocking layered acidizing and chemical working fluid temporarily blocking acidizing tend to be commonly used.However,for offshore production platforms,due to space and cost constraints,it will be better to choose the method with simple operation and high success rate.As the mechanical plugging acidizing needs to trip the pipe string,and the high positioning accuracy of the acidizing layer is required,the working fluid is considered to solve the plugging by using temporary plugging and diversion acid.Through research and the investigation of the existing temporary blocking diverters,it is found that the emulsion temporary blocking agent with low cost and easy access can meet the requirements of offshore oil field operation.After the water-in-oil emulsion enters the well,a high viscosity emulsion can be formed in the water layer to temporarily block the water layer.The crude oil will be diluted and dissolved in the reservoir,which can achieve the purpose of selective plugging,followed by uniform acidification.After investigation,several kinds of commonly used oil-in-water emulsifiers were selected and then the emulsifiers were compounded to enhance the emulsifying effect.Through the evaluation of the appearance,thermal stability,p H stability,viscosity and particle size of the emulsion,the emulsion temporary blocking agent was finally determined:diesel oil as the main agent,water as the auxiliary agent,oil-water ratio of 3:7 to mix and stir,and then add the selected emulsifier volume fraction of 3%to form a stable temporary blocking agent system.When we are evaluating the plugging characteristics of emulsion diesel temporary plugging diverter,the target well cores were selected for the physical model experiment.The blocking ability was evaluated by single core displacement and diversion effect by parallel core displacement.Through the single core displacement experiment,it is found that the emulsion liquid temporary plugging agent has a higher plugging effect on the high-permeability core than the low-permeability core,and the plugging rate is about 80%when the permeability is lower than 50×10^-3?m²,and over 90%when the permeability is higher than200×10^-3?m².In the parallel core displacement experiment,cores with different permeability were used to simulate the flow of adjacent oil and water layers in the formation,respectively.It was found that after the treatment with temporary plugging agent,the permeability of water layer decreased obviously,and the permeability of oil layer was less affected,indicating that the emulsion realized the effect of temporary plugging diversion.In addition,the mechanism of emulsion temporary blocking was confirmed by observing the particle size of emulsion.The particle size distribution of the emulsion is less than 12 m,mainly 2?m?6?m,and smaller than the radius of pore roar.Therefore,when the emulsion enters the pores of the formation rock,it is not blocked in the form of"throat-stuck",but by forming a highly viscous fluid in the water layer to reduce its flow efficiency and form flow resistance,so as to achieve the effect of diversion.The emulsion temporary blocking diverter screened by experiment has the characteristics of low cost,easy producing and simple process flow,and is suitable for offshore oil field.In the field construction,well selection and layer selection has a great influence on the success rate of operation,so it is appropriate to choose the well with high cementing quality,high water-bearing comprehensive index and strong inter-layer heterogeneity.In the process of circulating working fluid,it is suggested to use clear water slug as isolation fluid after extrusion of diversion agent into the formation,and separate it from subsequent extrusion of acidizing fluid,so as to prevent water layer emulsion from demulsifying in advance and affect the diversion effect.