Applications of Streamline Simulations to Reservoir Studies

Abstract

Abstract Computer models of oil reservoirs have become increasingly more complex in order to represent geological reality and its impact on fluid flow. Memory and CPU time limitations by finite difference/volume simulators force a coarser resolution of reservoirs models through upscaling. Upscaling can lead to significant difficulties in reservoirs studies:while the fine-scale geological model is build from petrophysical, log, and seismic data, its dynamic behaviour is never checked. As a result, a coarse-scale reservoir study can be linked to a fine-scale geological model but the two might be inconsistent in their dynamic behaviour.Conversely, the upscaled model cannot be properly tested since the flow and production behaviour at the fine-scale level is not available. There is no reference solution for guiding important decisions for building a consistent upscaled model.A large number of sector models are required in designing optimal well patterns. Streamlines simulation is now an attractive alternative to overcome some of these drawbacks since it offers substantial computational efficiency while minimising numerical diffusion and grid orientation effects. It allows the integration of fine-scale geological models into the reservoir engineering workflow. In this paper, we demonstrate the usefulness and efficiency of a streamline simulator (3DSL5) in the reservoir engineering workflow. We evaluate its speed, memory requirements and scalability using tracer and black oil test data sets on an SGI Origin 2000 (250 MHz MIPS). Our data are based on real fields and range from 200000 to 7 millions cells with cells as small as 30×30×0;5 meters. We examine problems with pre- and post-processing of large data sets and visualising such simulations. Streamlines allowed us to check the validity of a large geological model and to optimise wells patterns with more than 30 producers and injectors. Application of streamlines to the 10th SPE comparative solution project is also discussed. We demonstrate how streamline-based simulation has matured from a research tool to an industrial application providing real benefits to engineers as a complementary tool to existing conventional simulation technology based on finite volumes. Introduction Dynamic flow simulation is still a bottleneck in most integrated reservoir studies that attempt to reconcile the geological model with seismic data and well data. Three-dimensional, high resolution (3DHR) seismic data as well as improved 3D static modeling tools produce models that are ever more detailed and allow significantly more faults than the previous generation of static models. Today's fine-scale models are commonly in the range of 1 to 10 million cells. On the other hand, flow simulation technology based on finite volumes (FV) or finite differences (FD) is mature. Any improvements are expected mainly from parallel processing of key modules such as the simultaneous solution of the linearized flow equations or PVT calculations. As a result, only relatively small dynamic models (˜100000 active cells) can be considered in routine engineering studies. Dynamic flow simulation has also suffered from recent cost cutting by reserving large-scale computing power (machines with more than 1000 processors) to seismic processing, while shifting most other simulations to PC clusters with a limited number of processors (8 to 32). Upscaling fine-scale geological models remains a reality for most studies causing significant deterioration in the geological model. In many cases, the fine-scale and coarse-scale models do not superimpose, with coarse blocks being traversed by fine-scale faults. Under realistic reservoir conditions, rigorous upscaling becomes difficult forcing the engineer to make dubious approximation (fault location and transmissivity, layer resampling, etc). The fact that these approximations often cannot be quantified since a fine-scale reference solution is not available makes matters worst. A methodology that allows solutions on the original geological model is therefore desirable, allowing some quantification of errors due to upscaling. Streamline-based reservoir flow simulation is one alternative currently available1,2.