Description The field in question is a super giant oil field located in Southern Iraq. Historically, the field had 27 wells, along with surface facilities capable of processing ca. 100kbbl/d of oil. An additional processing facility was installed and some 18 additional wells were drilled and completed in the period 2012–13 to increase production levels in the field to more than 200kbbl/d, referred to as First Commercial Production (FCP). The field was shut-in for approximately 14 months during the pre-FCP period. Initially, only scarce historical pressure, well test and production allocation data existed and so an approach to prove up, manage and optimize field production performance was developed using Integrated Production System Modelling (IPSM). This involved both surface and subsurface disciplines collaborating to integrate stand-alone models and discipline data from operations, production technology, reservoir engineering, petrophysics and production geology into a single integrated model for proving up well capacity, field surveillance and optimization. Initially, the individual discipline model definitions were based on design case and oil field theoretical assumptions combined with single point(s) of actual data points. As more field data was collected the various models were updated and re-calibrated to ensure a maximum deviation of 10%. Over the past 3 years, as the field has transitioned from the pre-startup phase to the stable production phase and with this has been the evolution of the uses and application of the IPSM. This paper will describe the data gathered, process of model calibration, uses of the model in the four key phases to date along with the future aspiration case: Generally speaking, the main objectives of building and maintaining an integrated production system model are:

With limited and scarce subsurface and surface data, it becomes quite challenging to monitor a rather large field, having more than 50 wells actively producing, and actively optimize the production, achieving the desired production rates and maximizing the benefit for the operator and partners. The field in question was inherited from the previous operator, with 27 legacy wells, and a surface facility capable of processing ca. 100kbb/d of crude. Additional processing facility was installed to double the legacy capacity and 30 wells drilled by the time of preparing this paper for supplying the crude. The field had a shut-in period of 14 months in 2011-12 for various upgrades and surface works. It was then necessary to introduce an integrated modelling tool, to allow for a more efficient control and monitoring of the producing asset, combining all the components together and testing the interactions between the different system parts. The Integrated Production System Model (IPSM) was built based on the principle of following the oil molecule from the pore throat to the export. As such, it comprises of three main components, linking the subsurface to the surface, those are: –Reservoir Models (built with Petex® MBAL©)–Well Models (built with Petex® PROSPER©)–Trunklines/Flowlines and Separators (built with Petex® GAP©) Petroleum Experts® (Petex) develop the Integrated Production modelling software suite that comprises the tools mentioned above and are the company's proprietary. The current version of the IPSM is used in variety of situations; these include mainly but not limited to: ▪Medium Term Production Forecasting (MTPF)▪Production System Optimization (PSO)▪Opportunities assessment▪Identification of bottlenecks▪Further well scoping The IPSM has facilitated the application of many processes, allowing for a faster and more informed decision making, these include: ▪Optimization: as required and identified in PSO Meetings, optimization activities are carried out as part of increasing the total system production output, which adds more value to this process▪MTPF: generated on a monthly basis, the MTPF clearly highlights the production pitfalls, and the expected targets with a given set of assumption, and honouring the constraints that exist in the system, allowing for proper future planning, and the need for well scoping studies and highlight of the requirements to meet the desirable targets▪Maturing opportunities and assessing their system gains and impact on system This paper presents the process of building and maintaining an IPSM model throughout the different phases of a super giant field's life, from early production days with limited wells and data to the point of having real time data transferred to the office, fully utilizing the available data help make decisions that maximizes and eliminates waste.

One of the principle inputs to project economics and all business decisions is a realistic production forecast. This becomes particularly challenging in supergiant oil fields with medium to low lateral connectivity. In this case, three distinct production forecasts were generated: Short Term (ST) – 3 monthsMedium Term (MT) – 2 yearsLong Term (LT) – 5+ years The main objectives of the Medium Term Production Forecast (MTPF) are: Provide an overview of the total expected production profile, expected wells potential/ spare capacityHighlight the requirements to maintain production targetsProvide an anchor point for the ST and LT production forecast generation The main tool used for MTPF was Integrated Production System model or IPSM (GAP © PETEX) since it can predict reservoir behavior, honor physical constraints and capture bottlenecks and back-pressure effects within the production system. The different components of the IPSM are the reservoir component, well component and surface network. This paper covers the methodology for building the reservoir component of the IPSM to evaluate and accurately predict reservoir performance in the MT period. The IPSM model is not only used for the MTPF generation, but also for real time Production System Optimization (PSO), key decisions regarding well hookups, etc. by the Well, Reservoir and Facility Management (WRFM) team. There was a business need to build a pragmatic IPSM model with an optimal run time. Thus, tank models were built to replicate the 3D reservoir models which had been built in MoRes™ (dynamic reservoir simulator developed by Shell). The MoRes™ model was divided into multiple sectors (tanks) based on pressure sinks predicted by the model and supported by geological studies. From the MoRes™ model, a Grid cell Pressure histogram (Pressure versus frequency plot) was used to divide the reservoir into certain sectors. A close-to-normal distribution per sector was obtained to divide the reservoir into an optimal number of representative sectors. This was done because a single pressure value per sector is used by the well models connected to the sector to calculate the inflow performance in IPSM. Acquired Static Bottom Hole Pressures (SBHPs) in wells were used as anchor points for the calculated average pressure of the sectors and to test the validity of the divided sectors. This methodology has been tested successfully in the stated super giant oil field, which has both sandstone and carbonate reservoirs. An example this is covered in the paper. It was concluded that utilizing multiple sectors (tanks) results in reservoir pressure decline predicted being closer to what is actually seen by the wells. The IPSM model built represents reality sufficiently well in the MT period, thus increasing confidence in the generated production forecast. Another technical advantage of the described method is the higher sustainability of the model. The suggested histogram method, in combination with geological information available, can be applied to majority of the reservoirs. This combination is paramount to ensure the divided sectors concur with reality.