Sonatrach in Algeria needs to find opportunities and expand the recoverable reserves from a complex brown oil field located in the South East of Hassi Messaoud field (Giant oil field in Algeria). This field has been produced for more than 14 years from two complex reservoirs (lower Claystone Triassic TAGI & Ordovician Quartzites QH). The field has been produced with 5 main wells under natural depletion regime. This paper demonstrates the integrated multidisciplinary work which has been developed to construct a reservoir model and come up with development forecast scenarios for oil reservoir field to evaluate un-connected volumes & improve the actual field ultimate recovery with the complexity of the field and the high uncertainties. The workflow has been started by checking the seismic interpretation for the area. Second step was to QC (Quality Check) the logging cores and reservoir petrophysics evaluation well results. Pseudo functions were generated for both reservoirs based on water saturation profiles versus height. In order to segregate the saturation profiles according to the rock quality we have generated petrophysical litho-facies logs based on cutoffs applied on porosity and permeability logs. Five (5) litho-facies have been defined & good saturation match was obtained at well level. The hydro carbon volumes were calculated based on an ODT (Oil Down To) at −3549m TVDSS (Total Vertical Depth Sub Sea), using porosity, NTG (Net To Gross) & saturation models. Reservoir characterization was also achieved by integrating all available geological data with the extensible dynamic data (pressure build-up data, 15 years production data, PLT/MDT (Production logging Tool / Modular Dynamic Test) data). First the volumes have been matched between static and dynamic model with less than 1% error. The second phase of dynamic modeling was to calibrate the model versus the observed data, for that global modification has been applied to preserve the geological heterogeneities & main parameters were fault transimissibilities, & in absence of kv/kh ratio, sensitivity on this parameter has been also applied & considered. The last phase was to put in place the forecast scenarios. Based on the field challenges and actual behavior the bellow scenarios have been evaluated: – Base case: No further action scenario – Convert existant wells cases (Workover): convert producer with high water cut to water injector – Hydraulic fracture scenario cases A 3D geological model which allows a good predictivity of oil production and pressure regime was constructed for a complex and tight oil reservoir; this has helped to achieve the history matching with minimum modifications and allowed to optimize the field development plan with higher oil recovery factor between the evaluated scenarios highlighted above. The results of the dynamic simulation modeling indicate some potential undrained hydrocarbon areas which are promising for future development. As a result, & among the tested forecast scenarios, one of the existing wells was proposed to be converted into a water injector, this would help to increase the sweep for the other existing wells & improve the final recovery in field. Also, scenario of hydraulic fractures has been evaluated for two existing wells and it has showed also big improvements of the final field recovery.