民和盆地油页岩加热过程储集物性研究

Study on Reservoir Physical Properties of Oil Shale During Heating in Minhe Basin

为明确加热排烃对油页岩储集物性的影响,选择民和盆地未成熟油页岩为研究对象,经低温干馏,利用裂缝三维扫描、高压压汞、低温氮气吸附、X射线衍射等分析手段,对不同加温阶段的油页岩样品进行储集物性分析,进而揭示油页岩加热过程中储集物性的演化规律。结果表明,在低温加热阶段(185~350℃),油页岩少量排烃,油水产率和半焦产率变化较小;中温加热阶段(350~475℃),油页岩大量排烃,油水产率和半焦产率大幅度上升;高温加热阶段(475~520℃),油页岩残余排烃,油水产率和半焦产率基本不发生变化。在油页岩的加热过程中,随加热温度上升,裂缝数量逐渐增多,微小裂缝逐渐加宽并延伸,进而相互沟通连接形成大裂缝,且裂缝主要发育在层理面,垂直层理面方向并未产生明显裂缝;油页岩比表面积逐渐增大,孔隙由微孔向大孔转变,并且随着油页岩大量排烃,部分大孔互相连接沟通形成微裂缝;油页岩半焦的吸附量随着相对压力和温度的升高而升高,黏土含量减小,伊蒙混层中的蒙脱石构造坍塌,逐渐向伊利石转化,矿物颗粒减小,导致泥岩中产生微裂缝,从而使泥岩的孔隙度和渗透率增加。

In order to study the influences of heated hydrocarbon expulsion process on reservoir physical properties of oil shale,selecting the immature oil shale in Minhe basin as the research object,reservoir physical properties of the oil shale samples in different heating stag es are analyzed by means of 3D scanning observation of cracks,high pressure mercury intrusion experiment,low temperature nitrogen ad sorption and X ray diffraction analysis after low temperature carbonization,and the evolution of oil shale reservoir physical properties dur ing heating are further revealed.The results show that in the stage of low temperature heating(185-350℃),small amount of hydrocarbon is expulsed from the oil shale and the production rates of oil water and semicoke change a little;in the stage of medium temperature heating(350-475℃),large amount of hydrocarbon is expulsed from the oil shale,the production rates of oil water and semicoke significantly rise;in the stage of high temperature heating(475-520℃),residual hydrocarbon is expulsed and the production rates of oil water and semicoke remain the same.During the heating process of the oil shale,as the temperature rises,the amount of cracks increases,micro cracks widen and extend and then large fractures are formed.The fractures are mainly developed at the bedding surface and there are no obvious frac tures on vertical bedding surface.The specific surface area of the oil shale gradually increases,micro pores become large pores.With the expulsion of hydrocarbon,partial large pores connect with each other and micro fractures are formed.The adsorption of the semicoke in the oil shale increases with the rise of relative pressure and temperature and the clay content decreases.The smectite in the illite/smectite for mation gradually transforms into illite,the grain sizes of minerals desease,leading to the forming of micro fractures in mudstone and finally the porosity and permeability of mudstone increase.