Abstract
As a kind of potential new clean energy, natural gas hydrates (NGHs) have become a new hotspot in exploration and development. However, the sand production problem in the exploitation of NGH reservoirs seriously restricts the commercial exploitation of NGHs, so the research on sand control in hydrate exploitation is particularly important. In this study, an actual NGH reservoir in the South China Sea was experimentally simulated and sand control experiments were carried out on four different types of sand control elements. Furthermore, the factors, such as pressure, temperature, permeability, the amount of sand production and structure of reservoir skeleton in experiments were analyzed and plugging mechanisms of sand control elements were studied from the microscopic perspective. It is found that the sand production is mainly concentrated in the early stage of the experiment. Moreover, the failure of the reservoir skeleton is shown as non-uniform extension around, and the reservoir skeleton near both sides of the well wall is more seriously damaged than that to the inward. In the sand control experiment, the higher accuracy of sand control elements is, the smaller cumulative sand production, and the morphology of the reservoir skeleton is basically maintained. The experiment shows that the sand control medium is mainly plugged in the radial (Particle agglomeration-induced plugging) and axial (Fine particle invasion-induced plugging) directions, and particle agglomeration-induced plugging and fine particle invasion-induced plugging jointly act on the sand control medium. A water film and fluid flow on the surface of the sand control medium can accelerate particle agglomeration. Sand control elements made of hydrophobic materials can reduce the degree of plugging of the sand control medium. The research results are conducive to understanding mechanisms of sand control elements plugged by gravel during the exploitation of hydrate reservoirs and provide reference for future sand control design.
NSTL