Productivity and oil fingerprinting: Application of analytical chemistry in the assessment of reservoir quality

The ability to understand and possibly even predict the productivity of wells across a field is an important accomplishment in a production setting. In the tight Lower Cretaceous chalk field Valdemar, 5 wells have been observed to produce significantly larger oil volumes compared to nearby wells. This study was conducted to map the inter-well differences in the oil composition to better understand the productivity differences. This was done by analyzing any chemical differences of 21 samples from 16 different wells by GC-MS and principal component analysis of summed extracted ion chromatograms (SICs) using the chemometric analysis of selected ion chromatograms (CHEMSIC) method. The sterane (m/z 217 and m/z 218) and C4 (m/z 234) biomarker SICs were found to have chemically meaningful features described by principal component 1 (PC1). The association between these markers and the relative production was modeled to provide a better understanding of the productivity of the different wells. A correlation between oil saturation and productivity was established in the sense that the more mature and thus less viscous oil seem to have charged certain favorably placed reservoir sections first; these locations coincide with the location of the 5 wells in question.