Streamline Technology: Reservoir History Matching and Forecasting = Its Success, Limitations, and Future

Abstract

Although reservoir flow simulation is a mature technology, there is a general lack of understanding in the oil and gas industry as to when it should be applied, the limitations of it and how recent technical improvements have changed simulation. Streamline models have dramatically changed simulation work and made predictions better. Simple workflow and quality control issues are absolutely critical to insuring reasonable forecasts. There are various technologies that will substantially improve simulation forecasts and reduce error bars. Some of these new technologies are:Streamline based flow simulationAssisted history matching (AHM) techniquesFour dimensional seismic (time lapse 3D seismic)Parallel computingIntegrating flow simulation with geo-mechanical effects. This article focuses primarily on the first two points. Streamline Based Flow Simulation Streamtube and streamline technology, to a large extent, have been driven by the realization that heterogeneity controls recovery factors for many fields. This realization caused the derivation of more complex geological models, but unfortunately also highlighted the gap between geological detail and simulation capability. Streamtube technology was originally developed in the 1960s(1, 2). Two dimensional streamtube models were initially available for homogeneous permeability regular flow patterns, such as a five-spot pattern. Streamtube models were later generated for irregular well positions and areally heterogeneous reservoirs. Old streamtube models only allowed constant well rates and positions (i.e., no infill wells, no rate changes or the shutin of wells were allowed). Gravity effects, and therefore the vertical sweep efficiency were not always accounted for. Thus, streamtube modelling often could not allow for infill drilling or shutin wells, and streamlines were fixed in space. As a result of these limitations such early applications were limited and basically evaluated only the areal sweep efficiency of a pattern. To account for vertical sweep efficiency, Chevron(3) developed two-step hybrid streamtube models in which vertical cross sections were first simulated and then combined with areal streamtube models(4-6). Thus, vertical sweep, then areal sweep, were evaluated. However, infill drilling and large changes in production/injection rates meant that streamtube geometry changed resulting in limitations with this technique. Streamline technology is now practical in many field cases because it includes:Gravity3D effectsChanging well conditionsMultiphase flow. Streamline technology includes gravity effects and allows well rate changes (starting/stopping of wells)(7–11). This allows engineers to perform a one-step process that evaluates both vertical and areal sweep, and also accounts for well changes. There has been an explosion of studies that have highlighted the usefulness of streamlines(12-19). In many field situations gravity and vertical heterogeneity are important parameters for waterflood recovery. How Is Streamline Technology Different From Finite Difference Simulation? In a conventional finite difference simulation, there is a pressure-solve segment and a transport-solve (saturation) segment. In finite difference we solve for pressure then calculate flow based on the pressure distribution (for IMPES solutions), but flow transport is from block to block, whereas, in a streamline/streamtube simulation model, fluids are transported along streamlines, as shown in Figure