Study On Imbibition Mechanism Of Fracturing Fluid In Tight Sandstone Reservoir In W Area Of Ordos Basin

Tight reservoir with low permeability,low porosity,low pressure,high capillary pressure and high effective stress,often without natural reservoir capacity,must pass through the volume fracturing to obtain economic productivity.At present,the fracturing fluid flowback rate is generally lower than 40%,capillary imbibition is an important factor of fracturing fluid retention and absorption in tight reservoir,the study on fracturing fluid imbibition mechanism is very important to improve the volume fracturing economic benefit.The paper studies the reservoir characteristics in the W area to understand the imbibition conditions,then designs the imbibition experiment of fracturing fluid based on the imbibition theory,analysis the imbibition phenomena,the mechanical mechanism and the influence factors,uses suitable imbibition model to scale the experimental results,applies the experimental results to predict fracturing fluid imbibition displacement efficiency and fracturing fluid flowback rate.Research shows: the imbibition efficiency of brine system is higher,surfactant system is lower.The imbibition efficiency of different core permeability is between 14.94% and 21.4%,imbibition efficiency increases with the increase of permeability,but when the permeability is too large,the imbibition efficiency has a decreasing trend.When other physical conditions are equal and the water phase viscosity is constant,the imbibition efficiency decreases with the increase of oil viscosity.About different boundary conditions,the imbibition time is between65 h and 185.5h,the imbibition rate is different but the final efficiency is quite.The imbibition rate is greater with smaller the core and smaller the characteristic length.The shut in time has a great influence on the flowback rate of fracturing fluid,the suction velocity of fracturing fluid is far greater within 40 days after shut in.