Low Cost Viscosity Reduction Technology For Heavy Oil In Tight Reservoir In M7 Block

The reservoir of M7 block in San tang hu Oilfield has poor physical properties,with characteristics of medium-high porosity,ultra-low permeability,and high oil saturation,and belongs to abnormal low temperature tight oil and heavy oil reservoirs.Due to the deep burial of the reservoir,the unusually low temperature of the formation,and the high viscosity of the heavy oil,the measures such as the multi-element heat flow,nitrogen stimulation,and atomization viscosity reduction carried out in the early stage were less effective.Emulsified viscosity reduction technology has become one of the important technologies for efficient development of heavy oil due to its advantages such as good viscosity reduction effect,mature technology,low cost and wide application range.This paper studies the feasibility of emulsifying viscosity reduction technology in M7 block.Through the design of orthogonal experiments,a new composite viscosity reducer CSY-1 was developed,with a formula of 0.5%OP-10,1.8%SDBS,0.1%Tween80,and 1%NaOH.This type of viscosity reducer has good dispersing and emulsifying ability through the synergistic effect of multiple ingredients.Emulsify the M7 block heavy oil with acid value of 5.8mg KOH/g and 11600 m Pa·s into an O/W emulsion at 50~oC and oil to water ratio of 7:3.It is superior to the other three commonly used viscosity reducers in oil fields.The effects of temperature,oil-water ratio,viscosity reducer concentration,NaOH and other factors on viscosity reduction were further studied.The results show that the temperature has little effect on the viscosity of the O/W emulsion formed by CSY-1.When the oil-water ratio is large,the W/O emulsion formed increases the viscosity of the heavy oil;when the oil-water ratio reaches the water content of the inversion phase,the emulsion will reverse to the O/W emulsion,and the viscosity is greatly reduced;As the oil-water ratio continues to decrease,the viscosity of the emulsion further decreases.As the concentration of the viscosity-reducing agent increases,the viscosity-reducing rate first increases and then tends to be stable.NaOH generates surfactants by saponification reaction with petroleum acid,which can reduce the viscosity of heavy oil.The effect of chemical stimulation of CSY-1 viscosity reducer on heavy oil production was studied by carrying out a simulation experiment on chemical filling of sand-filled pipes in the laboratory.The results show that the recovery rate of chemical throughput in three cycles reaches33.71%,which is an increase of 24.42%compared with water injection.Factors such as temperature,salinity and well time have a great influence on the effect of chemical stimulation oil recovery.Under the same conditions,the higher the temperature,the smaller the injection-production ratio,and the higher the oil production;the higher the salinity,the larger the injection-production ratio,and the lower the oil production;24h is suitable for the well.The numerical simulation results show that the application of CSY-1 viscosity reducer can increase the single well production from 3.74 t/d to 8.12t/d.The cost per ton of water after viscosity reduction and the unit cost of oil increase are 90 yuan/t and 542 yuan/t,respectively,with good economic benefits.