Abstract:

Main pay zones of tight gas reservoirs are usually multiple layers of stacked channel sandbodies. Commingled production of these layers is commonly challenged by unclear contribution from each layer and undefined boundaries of sandbodies. Considering the morphological characteristics and different boundary sizes of channel sandbodies in the layers, and according to the principle of equivalent flow volume, a model of multi-layer commingled production well in tight gas reservoir was established. Then, based on the theory of modern production decline analysis, a method for determining the boundaries of channel sandbodies in tight gas reservoirs was proposed, and the production decline analysis charts for multi-layer commingled production wells were plotted. Finally, the production decline was discussed by boundary size, amount, and position of channel sandbodies, and the impacts of multi-layer channel sandbodies on production decline were clarified. The study shows that the production deline of multi-layer commingled production wells in tight gas reservoirs exhibits five stages. In the middle unsteady flow stage, it is possible to diagnose whether the boundary sizes of the sandbodies in each layer are equal. The smaller the range of channel sandbodies, the fewer the wide sandbodies, the smaller the proportion of wide sandbody, the poorer the stable productivity of the reservoir, and the more likely the increase in production decline rate occurs in the early and middle unsteady flow stages. The established method of production decline analysis provides a basis for evaluating the producing degree of each layer and determining reservoir stimulation treatments.

Key words: tight gas reservoir, production decline analysis, channel sandbody, multi-layer commingled production, sandbody boundary, flow model, parameter inversion