Abstract

Imaging X-ray Photoelectron Spectroscopy (IXPS) has been evaluated for its application to derive information on scale inhibitor distribution directly, and the wettability of pore surfaces indirectly, from a number of North Sea reservoir core samples. The technique derived elemental composition of an area of approximately 2 × 3 mm, with more detailed image mapping for individual elements over an area of 700 m.

An hexaphosphonate inhibitor was applied by both adsorption and precipitation methods. Phosphorous, a major component of the inhibitor, was only detected in the precipitated treated core. The level of detection though was below that necessary for more detailed mapping of inhibitor distribution. At this stage of the evaluation IXPS was found not to be appropriate for deriving detail of inhibitor distribution, however, results of this evaluation indicate that surface carbon distribution (wettability) is clearly affected by inhibitor treatment.

IXPS has also been used to compare different core cleaning and conditioning treatments of oil wet North Sea reservoir core samples. Results show that hot solvent cleaned core has a reduced mean carbon surface composition density relative to core that has been mild solvent cleaned. This confirms the removal of significantly more oil by hot solvent cleaning, indicating that core surface wettability characteristics are modified differently by different treatments, even though both treatments are thought to preserve an oil wet state.

Introduction

Wettability of reservoir rock is a critical parameter in reservoir characterisation Reservoir management and the understanding of oil recovery mechanisms require data on wettability, especially as it affects relative permeability and influences the effectiveness of production operations, e.g., surfactant-inhibitor treatments against scale formation. Current techniques for the measurement of wettability are unreliable and can take many months to complete. IXPS can derive such information rapidly.

IXPS also has potential to be implemented to a number of wider applications during reservoir evaluation. It can derive information on the distribution of elements which may relate to core mineralogy or from chemical treatments applied i.e. scale inhibitors.

Objectives

To evaluate the effects of different core cleaning methods on wettability.

To evaluate the application of surface analysis for mapping inhibitor distribution.

To evaluate the use of surface analysis to correlate 'wettability' and/or inhibitor distribution with reservoir framework mineralogy.

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