准噶尔盆地玛西斜坡区百口泉组砂砾岩埋藏溶蚀作用实验模拟研究

Experimental Simulation of Burial Dissolution of Conglomerate Reservoir in Baikouquan Formation in Western Slope of Mahu Sag,Junggar Basin

准噶尔盆地玛湖凹陷西斜坡区百口泉组发育低孔、低渗强非均质性砂砾岩储层,溶蚀作用显著,但溶蚀作用影响因素不明确。采用质量浓度2%的乙酸溶液代替埋藏条件下的有机酸,开展开放体系、高温高压溶蚀物理模拟实验。为研究有机酸溶蚀砂砾岩后储层物性、孔隙结构的变化,以及温度和泥质含量对溶蚀作用的影响,开展了两组溶蚀实验。结果表明:1)开放体系高温高压条件下,有机酸溶蚀砂砾岩中长石组分可以有效提高储层孔隙度以及渗透率,溶蚀显著增加半径10μm左右的小孔隙和小喉道,对渗透率的改善效果尤为显著;2)有机酸溶蚀模拟实验反应后溶液中析出的主要阳离子(Al^(3+)、Si^(4+)、Na^(+)、K^(+)、Ca^(2+))表明斜长石和钾长石发生溶蚀,并且温度越高,泥质含量越低,长石溶蚀量越大。综合分析认为,在开放体系下,较高地温、较低泥杂基含量的砂砾岩有机酸溶蚀增孔效率更高,这一认识可为下一步寻找有利储层发育区提供理论支撑。

The Baikouquan Formation in the western slope of the Mahu Sag of the Junggar Basin is a conglomerate reservoir characterized by low porosity,low permeability and strong heterogeneity.The dissolution is significant,but the factors influencing dissolution are not very clear.The present simulation experiment of dissolution in an open-flow system at high temperatures and pressures was carried out using an acetic acid solution with mass concentration of 2%to simulate organic acid action under burial conditions.Two groups of dissolution experiments were carried out to study the changes of reservoir physical properties and pore structure of the conglomerate after organic acid dissolu⁃tion,and the influence of temperature and matrix content on dissolution.The results show that:(1)In a high-temper⁃ature and pressure open-flow system,organic acid effectively improves the porosity and permeability of the reservoir,and increases the number of pores and throats with radius of about 10μm.The permeability improvement was particu⁃larly significant.(2)The main cations(Al^(3+),Si^(4+),Na^(+),K^(+),Ca^(2+))precipitated from the organic acid solution indicate the dissolution of plagioclase and potash feldspars.Samples with lower matrix content experienced more feldspar dis⁃solution at higher temperatures.This result is helpful in providing theoretical support for finding favorable reservoir development areas in the future.