Abstract
Since the beginning of pre-salt exploration, Petrobras has been using matrix acidizing to stimulate carbonate reservoirs, resulting in significant increase of productivity.
Over time, the learning curve has depicted the techniques improvement, leading to lower operation duration and costs and productivity increase. First well tests were performed without previous stimulation, revealing considerable amount of damage and, in some cases, it wasn’t even possible to flow the well without prior acidizing, both situations demanding a second test to assure evaluation objectives achievement. Considering acid job impact, it was decided to always stimulate the wells prior to well testing or production. Operation average duration continuously decreased from 15 days to hours. Treatment volumes, acid systems and chosen strategies were refined while well completion techniques have been developed.
Despite high productivities, as completion intervals got longer and higher permeability contrasts were exposed, well designers were still concerned about Recovery Factor reduction due to inefficient acid diversion. Therefore, stimulation requirements have been influencing well completion design.
Petrobras has developed a database to keep acid operation information, which made possible to get to relevant analysis presented in this paper, connecting information from different fields and well completion designs. Also, estimates of the impact of diversion in stimulation on Recovery Factor are presented along with improvement strategies, considering Pre-Salt scenario.
