Physical simulation experiment on flow characteristics in a low-pressure reservoir under co-production

To study the flow characteristics in a low-pressure reservoir under co-production conditions, a “one well with four layers” physical simulation was performed by constructing a physical simulation experimental platform and evaluating the calculation principles of the flow characteristic parameters.The results indicate that the flow velocity and deflection angle are related to the position of the flow starting point.As the angle between the line from the flow starting point to the wellbore and the horizontal direction changes from 0° to 90°,the horizontal velocity component gradually decreases, and the vertical velocity component gradually increases until it becomes dominant.The confluence effect in the wellbore results in a decrease in velocity, to a certain extent, in the central area of the reservoir.Based on the phenomenon of interlayer interference in a low-pressure reservoir under co-production, this entire process can be divided into a non-disturbance stage and disturbance stage.In the non-disturbance stage, with a decrease in the distance between the flow starting point and the wellbore, the flow direction converges toward the best trend line direction, and the deflection angle trends toward 0°.The flow path far from the wellbore is approximately parallel and exhibits parallel flow, whereas the overall flow trend near the wellbore is influenced by the area around the wellbore and exhibits radial flow.In the disturbance stage, when the pressure of the flow field, formed by the interactions between the fluids produced by each layer in the wellbore, is greater than the reservoir pressure in the low-pressure reservoir, gas invades the low-pressure reservoir and changes the direction of flow in the reservoir.When the distance between the flow starting point and the wellbore decreases, the deflection angle between the flow direction and the best trend line direction trends toward 180°.Additionally, the flow takes the form of radiation from the wellbore to the surrounding reservoir.In production layer combination, the coal reservoirs with small interlayer pressure differences should be selected to optimize the co-producing compatibility, reduce the interference degree of each coal reservoir, and avoid the phenomenon of backflow and gas production inhibition in low-pressure reservoirs.