Comparative Analysis of Damage Mechanisms in Fractured Gas Wells

摘要

Productivity impairment in tight-gas formations is a typical phenomenon for fractured wells. Processes responsible for this behavior are related to the characteristics of the porous media, and are induced as a consequence of the fracturing process. Fracture damage has been discussed in the literature for decades. In almost all cases, effects were considered in isola- tion. This is often not appropriate since natural effects such as stress dependency, fracture closure, and non-Darcy u0003ow are in- terdependent. The same applies for the cleanup process where the back production of the loadwater from the leakoff zones can be inu0003uenced by mechanical damage caused during the fractur- ing process, or by capillary forces and the gel residues of un- broken fracturing u0003uids within the fracture plane. This study analyzed the most common damage mechanisms by means of both generic and real u0002eld data. The latter was taken from German Rotliegend gas wells, which were history- matched and used for the evaluation of their cleanup and long- term production behavior. The results obtained were used to rank the individual processes for their damage potential. In ad- dition to a commercial model, a customized in-house simulator was required in order to capture the speciu0002c physics. Results suggest that the consequences of processes independent of the reservoir conditions are not negligible when compared to the damage induced by the fracturing itself. In particular, in tight-gas, the stress dependency of the reservoir rock and frac- ture closure both tend to have a signiu0002cant impact on the long- term productivity. Furthermore, inertial non-Darcy u0003ow can cause much higher production impairment than, for example, hydraulic damage. It also shows that low permeability reser- voirs are more affected by non-Darcy u0003ow effects in both the fractures and the reservoir than is generally assumed.