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 Q^2/3. 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.