The Effect of Geologic Parameters and Uncertainties on Subsurface Flow: Deepwater Depositional Systems

The application of reservoir simulation as a tool for reservoir development and management is widespread in the oil and gas industry. Moreover, it is recognized that the results of any reservoir simulation model are strongly influenced by the underlying geologic model. However, the direct relationship between geologic parameters and subsurface flow is obscure. In this paper we explore this relationship in a deepwater depositional system using data from two reservoir analogs: the shallow seismic dataset from the Mahakam Fan and outcrop data from the Brushy Canyon Formation of West Texas. Shallow seismic data from the Mahakam Fan area shows a high-resolution deepwater channel-levee system consisting of 10 migrating channels. Using an experimental design framework and a series of three increasingly complex models, we investigated the effect of nine different geologic factors on several different measures of the flow behavior. Our results show that, as expected, different geologic factors influence different measures of the flow. Most significant is the clear effect that the proportion and organization of the different internal facies making up the channels have on the recovery factor and net oil production. The Brushy Canyon outcrops used in this work represent sand-rich proximal deposits of a distributary lobe complex. Here we built models on a very small length scale to investigate the effects of sheet-like reservoir architecture as well as internal facies distribution of the sheets on subsurface flow. Again, an experimental design framework was employed, this time to examine the influence of 11 input variables. The proportion and organization of the internal lobe facies has a significant influence on the subsurface flow here but in these distributary lobe complexes other variables, including the stacking of the lobes, were also found to be important. The models in this study address flow behavior in deepwater, sparse well environments. Using models from the simple to the complex, we found that several parameters incorporated in the complex models, and not in simple models, had a significant impact on the predicted flow. Introduction The use of reservoir modeling and simulation is common in the oil and gas industry. Indeed, virtually every major oil and gas reservoir is studied or managed using earth modeling and reservoir simulation. Nevertheless, the relationship between input geologic elements and subsurface flow is not generally obvious. The objective of this work is to examine this relationship in detail for deepwater depositional settings. The link between geology and subsurface flow has been examined extensively in the literature. For example, Larue and coworkers have looked at fluvial systems using both conceptual models and the Meren reservoir. They examined a large number of models in an effort to investigate the largest possible variety of geologic interpretations and found a very wide range of resulting behavior (200% variation in breakthrough time and a factor of two variation in oil recovery). They also established that less ‘complex’ models could be built and capture the full range of subsurface performance results in their study. In another example, Jones and co-workers looked at both low and high net-to-gross fluvial reservoirs. In their study of low