New technique for determining rate dependent skin factor & non-Darcy coefficient

- Introducing new technique for determining rate dependent skin factor and non-Darcy flow coefficient for conventional and unconventional gas reservoirs.
- Using steady state pressure drop for predicting rate dependent skin factor for horizontal wells producing from finite acting gas reservoirs.
- Developing a set of plots for rate dependent skin factor considering different reservoir configuration, wellbore length, and anisotropies.
- The study emphasizes the ability to estimate rate dependent skin factor without the need for experimental work or using currente empirical models.

A non-Darcy flow develops in porous media when the velocity of reservoir fluids becomes extremely high because of the continuous narrowing of the cross section area of the flow and the convergence of flow streamlines. Therefore, the inertial effect increases significantly and the total pressure drop, required by fluids to move from the outer drainage area towards the wellbore increases significantly due to the extra pressure drop caused by the non-Darcy flow. The extra pressure drop is described by the Forchheimer equation in which the deviation from Darcy's law is proportional to the inertial factor which in turn is a function of porous media characteristics such as permeability and porosity.This paper introduces a new technique for estimating rate dependent skin factors (DQsc) and non-Darcy flow coefficients (D). The new technique uses dimensionless pressure for steady state flow to determine these two parameters. A set of plots has been developed for the term (DQsc) based on reservoir configurations i.e. reservoir boundaries (2xe & 2ye), wellbore length, and anisotropy. All the plots have been developed based on the fact that the rate dependent skin factor represents the difference between the total pressure drop and the pressure drop caused by Darcy flow only when non-Darcy coefficient equals to zero. Dimensionless pressure drops for horizontal wells producing from finite acting reservoirs have been calculated for steady state flow when the impact of dimensionless time can be eliminated. The calculated pressure drops have been used in reservoir performance models to estimate rate dependent skin factors and non-Darcy coefficients.A point of special interest in this study is the ability to estimate these two parameters without the need for experimental work or the need to use currently proposed empirical models for calculating them. This new technique requires knowing reservoir configurations (reservoir width and length), the length of the wellbore, and the height of the formation in addition to the anisotropy. The study indicates that rate dependent skin factors and non-Darcy coefficients have the minimum values when the reservoirs having square-shape drainage area. It has also been found that both parameters have great impact on wells with short wellbore length. Additionally, isotropic formations and symmetrical wells perform better than anisotropic formations and asymmetrical wells in terms of extra pressure drop caused by non-Darcy flow.