WETTABILITY OF OIL-PRODUCING RESERVOIR ROCKS AS DETERMINED FROM X-RAYPHOTOELECTRON-SPECTROSCOPY

Wettability has a dominant effect in oil recovery by waterflooding and in many other processes of industrial and environmental interest. Rec ently, the suggestion has been made that surface science analytical te chniques (SSAT) could be used to rapidly determine the wettability of reservoir materials. Here, we bring the capability of X-ray photoelect ron spectroscopy (XPS) to bear on the wettability evaluation of produc ing reservoir rocks. For a suite of freshly exposed fracture surfaces of rocks we investigate the relationship between wettability and surfa ce composition as determined from XPS, The classical wettability index as measured with the Amott-Harvey test is used here as an indicator o f the wettability of natural sandstones. The XPS spectra of oil-wet su rfaces of rocks reveal the existence of organic carbon and also of an ''organic'' silicon species, of the kind SI-CH relevant to silanes, ha ving a well-defined binding energy which differs from that of the Si-O species of mineral grains. We provide quantifiable evidence that chem isorbed organic material on the pore surfaces defines the oil-wetting character of various reservoir sandstones studied here which on a mine ralogic basis are expected to be water-wet. This view is supported by a strong correlation between C content of pore surfaces and rock wetta bility. The results also suggest a correlation between organic silicon content on the pore surfaces and rock hydrophobicity. (C) 1996 Academ ic Press, Inc.