Numerical simulation study on sand production during laboratory natural hydrate exploitation experiment

Abstract:

Nature gas hydrate (NGH) mainly exists in non-diagenetic strata which conducted the sand production restricting production of NGH. The numerical simulation was carried out by gas hydrate exploitation systemic illustrates the different production stages in the process of exploitation of natural gas hydrate reservoir pore pressure, radial strain, axial strain, axial displacement, radial displacement of the spatial distribution and change rule. TOUGH+hydrate and Abaqus were applied to conduct simulation of sand production. This experiment is simplified as a two-dimensional axisymmetric model. The results show: The radial strain appears to be deformed to the right and away from the wellbore during mining. The radial displacement in the mining process is always shown as the left displacement, near the wellbore; It is speculated that under the action of overburden stress, the right wall surface is a displace less rigid body, and the radial strain is manifested as the shear shrinkage phenomenon in the mechanical model, but the radial displacement of the reservoir is characterized as the wellbore displacement.(1) In the first stage of production, the pressure gradient is greatly affected by drainage and depressurization, and the radial strain is greatly affected by drainage step-down and initial strain variables; while in the stage of gas production, the pressure gradient is not only affected by the depressurization gradient of gas production, but also deflected by the overburden stress loading, where the radial strain of the reservoir changes little. (2) The axial strain presents downward strain. Although the entire axial strain is small, its axial strain gradient is not evenly distributed. (3) The radial displacement to the wellbore first increases and then decreases. In the first stage of production, the radial displacement is greatly affected by the drainage step-down, showing obvious displacement to the wellbore, and leading to partial sand production. However, in the gas production stage, the radial displacement of the reservoir is affected by the radial strain shear shrinkage, and its displacement decreases instead. (6) The axial displacement shows a downward displacement. Although the entire axial displacement gradient is uniform, the axial displacement difference is large.