Laboratory studies were used as an aid in designing stimulation treatments and to assist in the analysis of production results. These analyses were done in conjunction with coastal zone stimulation operations at the Department of Energy's Multiwell Experiment near Rifle, Colorado. A multitreatment stimulation plan was designed for the coastal zone because of apparent damage to the paludal zone formations in prior stimulation operations. The stimulation plan was made to minimize the use of water-based, gelled fluids. Two small stimulations were performed in the same coastal interval: an unpropped nitrogen gas frac and a propped, nitrogen foam frac. Gas production decreased from that of the gas frac after the nitrogen foam stimulation and formation damage was apparent. The laboratory program was used to (1) aid stimulation design; (2) help eliminate several possible causes of damage such as permeability degradation in the matrix rock, a gel block in the sand pack, proppant effects, or imbibition of brine from workover operations; and (3) examine the more probable causes, damage that may be centered around fluid effects in the natural fracture system. A unique explanation is not possible because there are some aspects of these damage mechanisms that cannot be verified in the laboratory. However, comparable damage mechanisms that have been seen in cracked core are described. Also, other postulated forms of fluid damage are discussed, largely in terms of natural fractures in core in combination with other measured core properties.

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