Wettability Determination: Pore Surface Analysis

Abstract

The nature of pore morphology and surface chemistry are inherent in determining the recovery performance of reservoir rock through their influence on relative permeability. Assessment of pore morphology can be made directly by using imaging techniques, although recovery prediction based on this assessment is still difficult. The surface chemistry of the pore structure can determine the very important pore structure can determine the very important parameter, wettability. Determination of the parameter, wettability. Determination of the most representative wetting state of the reservoir is essential to the laboratory core analyst, in order to establish representative relative permeability data. This paper discusses the application of surface science analytical techniques to the characterisation of the pore surfaces of reservoir material. Both inorganic and organic analyses have been performed on reservoir samples of known core performed on reservoir samples of known core properties. Techniques such as X-ray properties. Techniques such as X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS) and Laser Induced Mass Analysis (LIMA) have been used. Particular emphasis has been paid to the correlations generated between wettability parameters and the organic content on the pore surfaces. The work demonstrates quite clearly that direct analysis of the pore surfaces gives information pertaining to the wetting state. Further, pertaining to the wetting state. Further, chemical information is obtained which helps identify the functionality of organic species that leads to oil wetting character. The suggestion is made that the techniques outlined could be used to rapidly determine the wetting state of reservoir material. The surface analysis approach could also lead to a better understanding of how reservoir quality and wetting state can be modified, thus leading to improved predictive capabilities. Introduction The Pore Surface studies objective was initiated to examine the chemical characteristics of pore surfaces, primarily in the study of rock wettability. This has involved using ultra high vacuum surface science techniques and relating these results to existing special core analysis parameters. parameters. Wettability is defined as the tendency of one fluid to spread or adhere to a solid surface in the presence of other immiscible fluids. In reservoir presence of other immiscible fluids. In reservoir engineering, the solid surface is the rock matrix, and the fluids are either oil, water or gas. The wettability of reservoir material can vary from oil wet at one extreme, through various stages of neutral and intermediate behaviour to water wet. Wettability is an important parameter in oil recovery as it affects relative permeability characteristics by influencing the fluid distribution and capillary pressure characteristics of the reservoir. There are a number of techniques available for determining wettability. The Amott test is widely used through out the oil industry. It is a relatively simple test which provides an indication of wettability. However it takes several months to obtain the results. In addition to direct measurements, sample wettability can also be inferred from end point data generated during relative permeability tests. Oil wet samples tend to have a waterflood end point water relative permeability approaching, whereas water wet permeability approaching, whereas water wet samples have a suppressed end point, typically around 0.10. P. 351