Sonatrach in Algeria needs to meet its natural gas production targets to honor foreign sales contracts and domestic demand. As depletion drive gas fields, their reservoir pressure declines with an associated reduction in gas production. This phenomenon is more pronounced when aquifer water breaks through resulting in well-head pressures drop. This paper demonstrates how we developed several workflows serving construction of robust high-resolution simulation model to optimize gas recovery of mature field. The applied workflows started by reviewing seismic interpretation where different scenarios for velocity model were evaluated. Then followed by revising the petrophysics reservoir evaluations and developing a general deterministic for reservoir rock typing (RRT) and fluid contact identification. A pseudo-saturation modeling workflow was settled when SCAL data are missing. Control of channels bodies distribution in the model was achieved by applying a workflow that integrates all available geological data with interpreted dynamic data. Last workflow combining the defined RRT with generated maps of GIIP density, flow-capacity (KH) and actual reservoir pressure helped to identify the sweet spot locations for infill drilling option. A robust 3D geological and compositional dynamic model that allows accurate computation of LPG and condensates recoveries was constructed for a complex clastic reservoir in South-East of Algeria. No upscaling was applied on the static model to preserve its geological sense and getting high-resolution multi-million cell model. It replicates perfectly the reservoir pressure behavior and the 20 years of production history, allowing optimization of the field development plan. Among the multiple development scenarios that were investigated using the high-resolution simulator to reduce the run time, combination of infill drilling and mainly gas compression widely adopted by the petroleum industry and considered as a reliable method for improving reserves base was found to be the optimum development plan for the studied mature gas condensate field. Compression at wellhead from 75 to 20 bars extends well and field life resulting in tapping additional reserves of natural gas, LPG and condensates, which may be left behind in case surface compression facilities are not put in place in a timely and phased manner. By 2050, the final recovery factor (RF) of gas and condensates can be increased by 35% and 15% respectively compared to the existing development. The application of such integrated workflows in a structured, consistent and proactive approaches with the use of high-resolution simulator tool leads to have multiple scenarios/evaluations in a very short time and assure the ability to handle detailed geology and therefore reduce uncertainty in modeling outcomes. All of these will definitively improve the overall asset management in terms of maximizing production and recoverable reserves in similar complex clastic reservoirs from any part of the world.

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.