高含水稀油油藏蒸汽驱过程中原油组成性质的变化

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

在大庆葡Ⅰ组非均质砂岩油藏的葡71-75井区进行了稀油(地下粘度4.9 mPa·s)蒸汽驱试验.试验区水驱采出程度22.62%,综合含水82.87%,包含1口注入井和分属不同井网的7口采油井.取3口典型采油井,测定注汽前、注汽78天和120天时采出原油组成、性质的变化.结果表明,在汽驱过程中采出原油的密度、凝固点、含蜡、含胶质沥青质及运动粘度下降;初馏点显著降低(120℃→84℃→75℃),总馏量和300℃前各馏分量增多;50～90℃动力粘度在汽驱120天时最低,汽驱78天时略高于汽驱前;气油比增大;全烃分析表明汽驱后采出油轻质馏分增多,成熟度提高.基于前人关于蒸汽驱中产生热水蒸馏混合带的见解,利用所得分析测试数据,讨论了稀油蒸汽驱油机理:初期以热膨胀为主,中期为热膨胀、蒸汽蒸馏和降粘,后期为蒸汽蒸馏.图5表3参6.

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 oovers an injection and seven vroduction wells of various wellnet and is characterized by composite water cut 82.8% and recovery extent 22.62%. The changes in oomposition and properties are determined for the crude oil produced from three typical production weUs before steamdrive and during steam injection in 78 and 120 days. It is shown that during steamdrive the density, pour point, wax oontent, 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 ooncept 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.