Abstract
This paper shows a systematic approach to reduce uncertainty of volume, recovery factors and production forecasts with a closed loop of static and dynamic information over the life of the reservoirs. A case study of a Middle Marrat reservoir block in the North Kuwait Jurassic Complex (NKJC) is presented to illustrate the procedures. The NKJC comprises of six discovered fields each consisting of at least four prospective producing units containing multiple fluid types at near critical conditions. Intra-field compartmentalization due to fracture intensity, faulting and litho-facies variations resulting in porosity / permeability pinch outs has further created isolated blocks with a high level of uncertainty in the reservoir parameters describing the storage and flow characteristics necessary for forecasting well behaviors resulting from connected volumes. It is vital to collect as much dynamic data as possible at an early stage of the development for reserve booking and production forecast. Field development plan envisaged for the NKJC considered a three-phase development in order to mitigate CAPEX risk, reduce uncertainty and optimize recovery. Each phase has sufficient gap (3-4 years) to drill wells, collect formation evaluation and well performance data and adjust future plans as necessary. This paper describes the building blocks of volumetric estimates and fluid flow characteristics, considering the uncertainty levels in litho-facies spreads, porosity / permeability relationships, water saturations and fracture geometries etc. based on initial drilling and limited well tests. After the start of production, fluid properties monitoring, collection of well surveillance data such as pressure vs. rate curves, pressure transient analysis (PTA), production logging surveys (PLT), Modular Formation Dynamics Tester (MDT) and material balance calculations indicate another set of storage and flow properties. Integrating these estimates with geology, structural framework and fracture geometry is the key to obtaining a consistent reservoir description. Consistency in turn, reduces uncertainty in the connected volumes and flow dynamics over time. Flow assurance calculations using simulation model calibrated with the integrated set of parameters have been made with confidence to support a lifecycle reservoir management strategy to optimize recovery.
Case study illustrates that Green Field development plans benefit greatly from early dynamic data collection integrated with volumetric estimations by reducing uncertainty of reservoir description parameters that are used to calculate in-place hydrocarbon volumes and reserves. Reservoir uncertainty in naturally fractured carbonates is maximum with consequent risks. The methodology and work flow thus generated may be repeated for other blocks in the complex and for similar naturally fractured reservoirs.
