Testing the foundations of special core analysis

The project will use advanced mass spectrometric techniques to develop test protocols that can reduce uncertainty in data from special core analysis (SCAL). SCAL is a collective term for certain laboratory tests performed on petroleum reservoir rock (drilling cores) and fluids to determine important reservoir engineering properties. The most basic property at pore scale is the wettability of the reservoir rock with respect to the reservoir fluids. This largely controls the mobility of oil, water, and gas in the pore spaces and thus affects the oil production process. An ideal requirement for representative and reliable SCAL data is that core samples retain their original wettability when delivered to the laboratory. There is often a great deal of uncertainty associated with this. Common laboratory practice is therefore to clean out all reservoir fluids and possible residues of drilling fluid from the samples by various solvents and attempt restoration of the original wettability by well-controlled re-exposure of the cores to oil produced from the reservoir. Whether original wettability can be restored in this way will be investigated by comparing the mass spectrometric profiles of oil components extracted from the pore surfaces in core samples with the profile of oil produced from the formation. The mass spectrometric techniques to be used allow the determination of the molecular weight of individual oil components with a resolution high enough to identify the element formula of each compound. Comparison of the component profiles of adsorbed hydrocarbons and mobile oil can indicate whether the observed wettability of a reservoir core represents original reservoir conditions or are spuriously influenced by the treatment of the core prior to the SCAL analysis. More reliable laboratory data will lead to better operational decisions, less risk of failed investments and better chances of optimization, both in terms of extracted oil volume and energy use.

Special core analysis (SCAL) is a set of laboratory procedures to determine essential reservoir engineering properties like oil displacement, permeability and wettability by conducting various tests on reservoir material. These properties – wettability in particular – are important to assess the resources in place, estimate fluid flow characteristics and in developing optimal strategies for hydrocarbon recovery. More reliable laboratory data will lead to better operational decisions, less risk of failed investments, and better chances of optimization, in regard both to oil volumes recovered and energy expended. Wettability is the most basic rock-fluid interaction at pore level. It largely governs the mobility of reservoir fluids and their distribution in the pore spaces and thereby affects oil recovery processes. A fundamental requirement for representative and reliable SCAL data is that core samples retain their original wettability when delivered to the laboratory or that the original wettability can be restored. It is hypothesized that the most surface-active components in an oil, being minority oil components containing elements such as oxygen, nitrogen and sulphur, will adsorb on the rock surface and thus determine the wettability. If originally only present in small amounts these components might not be present in the mobile oil, and if they are removed during core preparation (by use of strong solvents) it will not be possible to restore original wettability. The uncertainties of SCAL related to wettability can be reduced by an increased knowledge about the minority oil components. The hypothesis will be tested on representative reservoir rock and fluid samples. Employment of cutting-edge high- and ultra-high resolution mass spectrometry techniques will be pivotal to the project. Comparison of the compound profiles of hydrocarbons adsorbed to the pore surfaces and oil produced from the relevant reservoir formation will be a key element of the analysis.