Numerical simulation of multi-layer co-production in marine-continental transitional shale reservoirs
Distinct sedimentary environments lead to notable disparities between marine-continental transitional shale and purely marine shale.This study develops a numerical model to evaluate the productivity of horizontal wells in vertically multi-lithologic superimposed reservoirs,focusing on the marine-continental transitional shale reservoirs at the eastern margin of the Ordos Basin.The model analyses the dynamic characteristics of single-stage gas well production under various lithologic combination modes.It particularly investigates key parameters such as coal seam permeability,the superposition relationships of reservoirs,and the impact of the production system on output characteristics.The findings indicate that:① In the early stages of combined extraction from coal-rich shale reservoirs,both gas and water are produced simultaneously.The gas primarily originates from the free gas in the sandstone and shale reservoirs,while the water is predominantly sourced from fracturing fluid and coal seam water.Notably,higher coal seam permeability correlates with increased cumulative gas and water production.② The optimal spatial stacking sequence for combined layer mining in coal-bearing superimposed reservoirs is identified as page-sand-coal.This sequence minimizes the interference of coal seam water production on the overall mining process.③ The production from coal seams exhibits significant stress sensitivity,impacting overall gas output.
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