Revised inflow performance relationship for productivity prediction from marine sandy hydrate reservoirs in Nankai Trough

Abstract

Productivity prediction is crucial for the safe and efficient exploitation of marine methane hydrate. As a feasible method, inflow performance relationship (IPR) can characterize productivity results and provide a theoretical basis for optimization of depressurization schemes. In this study, we propose two modified IPR models based on field data from limited trial production and numerical fitting in the Nankai Trough. Prediction results are obtained by depressurization, together with IPR curves under different recovery ratios. According to the conventional formulas, the reservoir pressure of the deliverability equation is revised, considering the dual contributions of hydrate dissociation and pressure drop. The comparison results show that the modified Vogel formula and Fetkovich formula can suitably describe the IPR for the single vertical well and horizontal well, respectively. Sensitivity analyses of various reservoir physical parameters indicate that changes in porosity and hydrate saturation cause diverse values for the undetermined coefficient A, primarily due to the alterations in the key coefficient pr′ in the revised Vogel formula for the vertical well scenario. However, absolute permeability has only a slight influence on the shape of the IPR curve. In contrast, absolute permeability plays a crucial role in affecting the Fetkovich-modified IPR curves for horizontal wells. Productions under varying porosities exhibit a consistent linear trend on the Fetkovich-modified IPR curve because of the comparable impact of gas production rate and pressure square variance. Besides, changing hydrate saturation can also have some effect on the IPR. Our research provides a feasible productivity prediction methodology for the safe and efficient extraction of similar hydrate reservoirs.