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.

One of the largest gas fields in the Sultanate of Oman was developed between 2010 and 2016 by drilling 26 vertical wells for commingled production from three deep tight gas sandstone stacked reservoirs. The shallower reservoir is a rich gas condensate reservoir, while the other two contain lean gas fluids. Over the last few years, the wells performance has been poorer than anticipated. An integrated study was carried out in 2016-2017 to identify the root causes of this under performance and eventually address it in a new field development plan. All subsurface and surface disciplines worked together analyzing available data in order to understand the production behaviour and complex nature of the field. One of the major findings of the integrated study was the interpreted presence of sub-seismic lineaments corresponding to possible zones of quartz sealed fractures. This was supported by seismic, core, reservoir pressure (MDT) and pressure build up data. The integrated data analysis revealed that these lineaments are having a direct impact on the field performance, as the hydrocarbon in-place volume seen by each well is dependent on the compartments defined by these lineament boundaries. A large set of lineaments were added to the dynamic model after mapping from detailed seismic work. This addition resulted in very good matches of historical production and pressure data. These updates to the reservoir model will ensure a more accurate field forecast and provide a better field development strategy. This paper will demonstrate that the presence of sealed sub-seismic fractures that may remain undetected can have a substantial impact on the performance of tight gas reservoirs. By identifying these sub-seismic elements and understanding their impact through an integrated approach, field performance can be better forecasted in order to account for the presence of these features.