A new laboratory procedure has been developed to study formation damage mechanisms and improve acid stimulation designs using an Environmental Scanning Electron Microscope (ESEM) coupled with core flood tests. An ESEM has the unique capability of observing a sample, wet or dry, in its natural, uncoated state. The core plugs used in core flooding experiments can be observed at the same locations, before, during and after treatment with workover and completion fluids, without any cleaning, drying or metal coating processes. The direct effects of the stimulation and completion fluids on the formation minerals can be seen along with any changes to the initial porosity. The ESEM is combined with energy-dispersive X-ray spectroscopy (EDS) to allow elemental analysis of precipitates or observation of changes in the elemental composition of the clay minerals.

This paper describes both the analytical procedures and the results of acidizing sandstone cores. The core material was observed by ESEM before, during and after laboratory core flood tests. This has resulted in a more effective acid stimulation treatment design through a better understanding of the fluid/rock interactions.

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