Changes in Composition and Properties of Light Crude Oil Produced from High Water Cut Sandstone Reservoir during Steamdrive

A steam flood pilot project for inhancing recovery of light crude oil(underground oil viscosity 4.9 mPa·s) has been performed in unit P71-75 of water-flooded,highly heterogeneous sandstone reservoirs of Formation P-Ⅰ,Daqing.This unit covers an injection and seven production wells of various wellnet and is characterized by composite water cut 82.8% and recovery extent 22.62%.The changes in composition and properties are determined for the crude oil produced from three typical production wells before steamdrive and during steam injection in 78 and 120 days.It is shown that during steamdrive the density,pour point,wax content,resin-asphaltene fraction,and kinematic viscosity are decreased;the saturated and aromatic hydrocarbon fractions are decreased initially and then increased;the initial boiling point is decreased significantly from 120℃ to 84℃ and further to 75℃;the total quantity of distillate and the quantities of distillate at different temperature ≤300℃ are increased;the gas-oil factor is increased;the dynamic viscosity at 50—90℃ is the lowest in 120 days and slightly higher in 78 days of steam drive than that before steam injection;an increase in light fractions and in maturity degree is observed during steam injection as shown by a total hydrocarbon analysis.Based on a previously published concept of hot water/distillate mixed zone in steamdrive and using the data of analyses and determinations,the light oil displacement mechanisms in steam flood are discussed as follows: thermal expansion in volume as main factor at early stage;thermal expansion,steam distillation,and reduction in viscosity at middle stage and steam distillation as controlling factor at late stage.