弱胶结储层微观出砂形态与出砂机理可视化实验模拟研究

宏观出砂规律模拟难以揭示微观出砂本质,为了探究弱胶结储层的微观出砂过程、形态与机理,开展了系列弱胶结岩心微观出砂过程模拟实验。实验使用不同浓度环氧树脂在80 ℃条件下固化2.5 h得到一系列不同强度的弱胶结岩心,采用显微放大手段观察不同胶结条件的岩心样品在流体驱替过程中的出砂形态演变过程及其最终出砂形态。根据实验结果提出了连续垮塌式、类蚯蚓洞式和孔隙液化式3种典型的微观出砂形态和出砂机理。通过分析,胶结强度和颗粒尺寸是出砂微观形态的主要因素;类蚯蚓洞式出砂形态下,出砂量m与驱替流量Q2/3大致呈线性关系;驱替流体对颗粒间胶结强度有削弱作用,长时间驱替可能诱使出砂加剧引起微观出砂形态转变;出砂形态是决定出砂量大小的重要因素,孔隙液化式的出砂量仅为类蚯蚓洞式的15%。初步形成的微观出砂形态与机理为后续微观出砂过程模拟、出砂规律定量预测提供了重要指导和依据。

Visual experimental simulation on microscopic sand production morphologies andmechanisms in weakly consolidated reservoirs

The macroscopic sand production laws can hardly reveal the microscopic essence of sand production. In order to explore microscopic sand production process, morphology and mechanism in weakly consolidated reservoirs, this paper carried out simulation experiments on the microscopic sand production process in a series of weakly consolidated cores. In the experiments, a series of weakly consolidated cores with different strengths were prepared by solidifying the epoxy resin of different concentrations under 80 ℃ for 2.5 h. Then, the microscopic magnification method was adopted to observe the evolution process of sand production morphology and the final sand production morphology in the core samples with different bonding conditions in the process of fluid displacement. And according to the experimental results, three typical microscopic sand production morphologies and mechanisms were put forward, i.e., progressive collapse type, similar worm hole type and pore fluid type. It is indicated from the analysis results that bonding strength and particle size are the main factors controlling microscopic sand production morphologies. In the sand production morphology of similar worm hole type, the sand production rate m is approximately in the linear relationship with the displacement flow rate Q2/3. Displacement fluid can weaken the bonding strength between particles, and long-term displacement can aggravate sand production so as to lead to the transformation of microscopic sand production morphology. The sand production morphology is an important factor dominating sand production rate, and the sand production rate in the microscopic sand production morphology of pore fluid type is only 15% that of similar worm hole type. These preliminarily concluded microscopic sand production morphologies and mechanisms provide important guidance and basis for simulating microscopic sand production processes and quantitatively predicting sand production laws.