恒速压汞法在致密储层孔隙结构表征中的适用性

Applicability of rate-controlled porosimetry experiment to pore structure characterization of tight oil reservoirs

在深入分析恒速压汞法原理的基础上,结合鄂尔多斯盆地延长组致密油岩心实验结果,研究了该方法在致密油孔隙结构表征中的适用性。结果表明:运用恒速压汞法能够区分孔隙和喉道,获得孔隙半径、喉道半径及孔喉半径比分布,可以更全面地表征孔隙结构并揭示其对渗流能力的影响;恒速压汞法以准静态进汞,能够消除润湿滞后效应,同时修正了高压下介质变形的影响,实验数据相比于高压压汞法更为准确。然而,受最高驱替压力的限制,恒速压汞法最大汞饱和度较低,无法表征半径小于0.12μm的孔喉。总体而言,恒速压汞法在表征致密油孔隙结构方面有一定的优势,但还需要结合其他方法才能表征致密油完整的孔隙结构。

With the deep understanding of theoretical foundation of rate-controlled porosimetry, tight oil reservoirs core samples from Yanchang Formation, Ordos Basin, were conducted to rate-controlled porosimetry to obtain pore structure parameters, and the applicability of rate-controlled porosimetry experiment was analyzed. Results indicate that rate-controlled porosimetry can identify pore and throat, get distribution of pore size, throat size and pore throat size ratio, thus characterize pore structure more effectively, and clarify the relationship between pore structure and flow mechanism. Comparing with pressure-controlled porosimetry, mercury is injected at quasi-static rate. Considering the porous material deformation under high pressure, the results of rate-controlled porosimetry is more accurate. However, restricted by maximum injection pressure, the total injection mercury saturation is low, and rate-controlled porosimetry fails to characterize pore with size smaller than 0.12 !m. The conclusion is that the rate-controlled porosimetry has advantages in characterizing pore structure of tight oil reservoir, while a combination of other techniques is also necessary.