Joint stimulation-water shut-off technology leads to extra oil from mature fields

There are number of challenges encountered in oil production of mature, depleted fields like naturally fractured complex carbonate reservoirs found in Oman and the Middle East Region. These include production under high water cut ranging from 90 to 99%, the presence of conductive natural fractures connected to the aquifer in the producing zones, multi-zone production and reservoir heterogeneities encountered in each zone. Conventional acid stimulation at such reservoir conditions is rather questionable, showing no economic value and exhibits very high risk of losing the remaining oil production with unwanted, further increased water production. However, acid stimulation combined with water control gives good opportunity for recovering extra oil using hydrophobic chains containing associative polymer. The polymer adsorption has double roles during and after the treatments acting as an acid diverter and water control agent as relative permeability modifier. In naturally fractured producing zones, this combined method shows lower risk and better potential than in those zones where matrix flow exists only. In summary, this paper will cover the theory behind the above-mentioned method, stimulation challenges, candidate selection, treatment design and the results of the campaign started since 2006 in one of matured fields in North Oman. The campaign focused on oil producing wells having more than 97 % water cut. These trials were the last chance for achieving acceptable oil production before abandonment. The main achievement of the campaign resulted in more than 207% incremental oil (net) added to the stock tank in parallel with 1.5% average water cut reduction. The technology will be applied in a bigger scale as part of production optimization.