Characterization and modeling of unsteady state relative permeability

Abstract

Relative permeability is a key factor in all kinds of multi-phase flow performance and reservoir engineering calculations in which it has a great influence in the full field development performance and optimum scheme selection. Accordingly, the accuracy of relative permeability has to be within acceptable and practical range of uncertainty level and that is the reason behind the old/new debate on what is the proper method of measurements and under what conditions the experiment should be conducted. Relative permeability measurements through Unsteady State method has been used as the default over the Steady State method for long time in most cases, since it is cheap, quick and assumed to be reliable. However, Unsteady State method has many uncertainties, since relative permeability profiles are determined after breakthrough occurrence (limited data range); moreover they are obtained using very sensitive interpretation procedures such as Johnson, Bossler and Naumann (JBN) and Jones Rosezelle (JR). This thesis topic has been selected due to the importance and necessity of such comprehensive investigation of Unsteady State relative permeability via analytical and numerical modeling approaches and its direct impact on field performance. Accordingly, the main objectives have been focused to address constraints/assumptions on the available Unsteady State experiments and numerical modeling sensitivity runs in order to comprehensively capture main characteristics and reliability of the method. In order to accomplish thesis objectives, different sets of relative permeability experiments have been gathered and analyzed from various producing fields in the region under different experimental conditions. Throughout this thesis, smoothness process of Unsteady State outcomes (JBN interpretation) has been examined to evaluate associated uncertainty levels. Moreover, in the carbonate core sample examined, it showed that only ∼ 25% of full saturation span is covered by Unsteady State, where almost three times this coverage saturation span is obtained by Steady State method. In addition, numerical modeling revealed that reference laboratory measurements (production, pressure differential and saturation profiles) can be matched through robust regression process under different approaches either 'Fully IMPLICIT' or 'IMREP' in which relative permeability and capillary pressure parameters are controlled. The outcomes of the modeling process illustrated that relative permeability profile is not a unique solution even under similar conditions. Thus, selection of the optimum representative profile that mimics actual multiphase flow in the reservoir should be based on uncertainty evaluation among various modeled profiles and comprehensive validation of the experiment procedure and conditions. This thesis will provide the reader with all related aspects of Unsteady State relative permeability in terms of necessary technical background, analytical investigation details and numerical modeling features and concerns, in order to produce representative relative permeability profile that has great influence in reservoir dynamics and field performance. Steady State tests, although time consuming, provides a robust and more reliable wateroil relative permeability in carbonate reservoir core samples.

Date of Award	2012
Original language	American English