Understanding the Effect of 3D Layering Methodologies on the Production Profile of Tidal Estuarine Reservoirs

Abstract

A typical tidal estuarine reservoir comprises inclined interbeds of sandstone and claystone, also known as Inclined Heterolithic Strata (IHS). This sub-seismic feature of naturally inclining beds, combined with considerable heterogeneity, commonly inhibits the horizontal connectivity and ultimately controls the fluid flow behavior within these systems. However, normal datasets from subsurface studies frequently restrict a full IHS characterization and lead to the construction of a conventional, proportionally layered reservoir model. Moreover, once the 3D model is carried forward for simulation purposes, any significant changes to the geomodelling parameters are commonly barred which leads to excessive manual near-well region editing. Therefore, this paper aims to showcase the importance of representing the architectural elements of tidal estuarine deposits in the 3D model and their relation to the 3D layering methodologies and reservoir performance through 3D outcrop studies and multi-scenario reservoirsimulation approach.

To demonstrate the effect of 3D layering on the production profile of IHS, 3D scanned outcrops of theBlackhawk Formation, USA, have been studied to produce several realizations of 3D models, including one that matched the morphological features of the outcrops as the truth case. All realizations were then simulated, and history matched to the truth case result as comparative studies.

Using 3 matched realizations to simulate 5-years forecasts, significant divergences prevailed. Cumulatively, there was up to 9% variation in total productions with only 3 producers and 1 injector wells in all realizations. More importantly, evident on both well by well production plots and visually over the time steps, the timing of water breaking-through the producer wells were faster and more uneven on the truth case, contrasting the results from proportionally layered realizations. Naturally, these required varying development strategies and proved that different3D layering methodologies produce quite variations in production forecasting albeit historically matched.

 The novelty of this work is to integrate geological concepts, in a form of 3D layering methodology, as one of the most influential variables when modelling tidal estuarine deposits with under-informed conditions. This work can be implemented further in most fields with layering uncertainties to enable an optimum flow estimation, for a better investment decision.