A Critical View of Current State of Reservoir Modeling of Shale Assets

Economic production from shale has been intimately tied to hydraulic fracturing since the first signs of success in Barnet Shale in the late 90s. The introduction of horizontal wells and multi-stage hydraulic fracturing was met by a huge move by operators towards developing shale formations that were mainly ignored in the past. Today using pad drilling, multiple horizontal wells share surface facilities and infrastructure, a development that minimizes the industry’s environmental footprint. To understand production from shale reservoirs one must understand the network of natural fractures in the shale and the role of hydraulically induced fractures and their interaction. In this article author proposes a new view of the network of natural fractures in shale that when interfaced with the induced hydraulic fractures, will provide a completely different picture of how stored hydrocarbon is produced. Modeling this new network of natural fractures and its interactions with induced fracture requires fundamental changes in our existing simulation models. Hydraulic fracturing has been around and been studied by engineers for decades. Analytical, numerical and datadriven models have been built to explain their behavior and contribution to flow. Contribution of natural fracture networks to storage and flow in carbonate (and some sandstone) reservoirs had led to the development of techniques to study and model them. Since they are the predominant source of connected porosity and permeability in shale, more attention has been focused on their characteristics in the recent years. Studies of methane production from coal seams in the mid 80s provided insights on sorption as a storage mechanism and desorption and diffusion as a transport phenomenon in reservoirs that came to be known as CBM (Coalbed Methane). Today, production from shale is mainly modeled based on the lessons learned in the past several decades where all the above techniques are integrated to create the modern shale reservoir models. In other words, we use the “Pre-Shale” technology to understand and model hydrocarbon production from shale. This may not be the most efficient path forward 1 . The coupling of hydraulic fractures and natural fracture networks and their integration and interaction with the shale matrix remains the major challenge in reservoir simulation and modeling of shale formations. This article reviews the methods used by the scientists and engineers in recent years to understand the complexities associated with production from shale. This will shed light on the commonly held belief amongst some of the best minds in reservoir engineering (those that have been intimately involved in modeling production from shale) that there is much to be learned about this complex resource and that our best days in understanding and modeling how oil and gas are produced from shale are still ahead of us. Furthermore, an alternative solution to the conventional simulation and moldeing currently used in the industry is proposed. This technology that is used and implemented today can enhance our understanding of production from shale. 1 Needless to say that there is much to be learned from the “Pre-Shale” technology. Nevertheless, hydrocarbon production from shale seem to be different enough to require a completely fresh look at the storage and transport phenomena as it is modeled today in our simulators. May be fluid flow through porouse media is not the dominant phenomenon and needs to be augmented and/or completely replaced by other modes of flow such as flow between parallel, diffiusion controlled, thin plates.