Experimental Study On The Distribution Rule Of Immiscible Fluids In Liquid Self-propping Fracturing Technology

At present,hydraulic fracturing technology has been widely used in the stimulation of unconventional reservoirs,and has achieved good results in improving oil and gas well production.Conventional hydraulic fracturing technology requires injecting solid proppants from the surface into the reservoir,then proppants are usually in the form of "sand bank"distribution to support fractures.However,conventional fracturing technology has disadvantages such as reservoir contamination caused by the gel breaking residue of fracturing fluid,abrasion to pumping equipment and tubular caused by high sand ratio with high displacement and pump pressure,sand plugging formed by improper control during sand filling process,as well as safety risk of both fracturing treatment and personnel,all of them affecting the application and development of hydraulic fracturing technology.To solve these problems,a new type of liquid self-propping fracturing technology is being developed.Its principle is defined as injecting two immiscible fluids into formation fractures,including self-generating solid fracturing fluid(SGSFF)and non self-generating solid fracturing fluid(NSGSFF),and SGSFF transforms to self-generating solid proppant(SGSP)under the stimulation of reservoir temperature to support fractures.This technology has four key aspects including phase transition material,phase transition control condition,distribution rule of immiscible fluids and oilfield treatment technology,and this paper is exactly to study the distribution rule of immiscible fluids,which is one of the four key technologies.In the reservoir fractures,the distribution pattern of SGSFF determines the distribution shape of SGSP,directly influencing the propping effect and fracture conductivity.Hence,it is of great significance to research the liquid-liquid two-phase distribution rule of SGSFF system for improving oilfield stimulation effect.This paper focuses on the sensitivity factors such as density difference,interfacial tension,viscosity ratio,injection pressure and injection ratio of SGSFF and NSGSFF,and has carried out the research of distribution rule of two immiscible fluids in liquid self-propping fracturing technology.The main contents are as follows:(1)By studying droplet stability,particle size and its uniform distribution extent of SGSFF,the influence rules of sensitivity factors on droplet shape distribution of SGSFF were analyzed,and the research scopes of sensitivity factors were preliminarily determined.(2)Using a physical simulation device for visualizing distribution in flat plate crack,this paper carried out the research of the influence regulations of those sensitivity factors on the distribution pattern of two immiscible fluids of SGSFF system in flat plate crack by utilizing single-factor controlling variables method.Different distribution patterns of SGSFF,such as bridge pier type,channel type and bead type have been found,and their formation conditions under single-factor influence were analyzed.(3)By using orthogonal experimental method,the influence rules of three factors,including viscosity,density and interfacial tension,on the distribution pattern of liquid-liquid phases of SGSFF system in flat plate crack were researched.At the same time,the influence regulations of injection pressure and injection ratio on the distribution pattern were studied.The formation conditions of different distribution modes under the functions of multi-factors were obtained,such as bridge pier type,channel type and bead type.It was found that the viscosity and injection pressure are the main factors affecting the distribution pattern.(4)According to the distribution physical models of SGSFF in flat plate crack under the influence of multiple factors,three-dimensional distribution geometric models of SGSP were established.Based on the mathematical model of fluid flow,the numerical simulations of flow field were carried out.The fracture conductivities under different distribution modes were calculated,and the distribution modes with high conductivities were preferred to select,such as bridge pier type and channel type.By using range method,the influence extent of viscosity,density and interfacial tension on the distribution pattern is as follows:viscosity is most,next is density,interfacial tension is least.This paper has revealed the distribution rule of immiscible fluids in liquid self-propping fracturing technology under the influence of different sensitivity factors,providing a reference for optimizing the treatment parameters of liquid self-propping fracturing technology and improving the fracture conductivity of reservoirs.