A New Integrated Workflow to Characterize and Model Shale Gas Fields

Abstract

Proper reservoir characterization and sweet spots identification for unconventional reservoirs need to be performed considering both geomechanical and petrophysical properties. This paper describes the integrated application of tools and technologies developed within eni internal research project on US Barnett shale gas. eni shale gas reservoir modeling has been performed by using a geologic workflow to link the petrophysical characterization and the seismic data at wellbore scale and consistently distribute these properties at field scale by means of a seismic "trend". This is the key to obtain a predictive geological model. In addiction, an engineering workflow that merges hydraulic fracture treatment, microseismic survey and advanced production analysis (APA) was set up. Thus the input parameters for dynamic simulation, focusing on the stimulated reservoir volume (SRV) estimation, may be obtained. A sector model was extracted from the full field geological model for dynamical simulation purposes. A "single porosity-like" approach was adopted to couple the advantage of dual permeability and single porosity models. As a first step, the History Match (HM) of gas production data and flowback water rates, was performed both at single well and pad scale. This allowed the tuning of SRV extension and permeability of the induced fractures. In addition, a comparison of gas reserves obtained by decline curve analysis and simulation model was performed. Moreover, by using the calibrated sector model, a series of sensitivities was carried out focusing on well landing and spacing in order to achieve an optimal pad design. The strength of this study lies on the integrated model approach. It is an efficient tool to drive and optimize the field development plan, allowing the definition of optimal wells spacing and lateral length, positively affecting economics. Finally, it is a robust approach to reduce uncertainties in gas reserves assessment. Introduction The largest part of global discovered hydrocarbon resources is stored in so called Unconventional reservoirs, that need advanced technologies, such as horizontal wells, multistage completion and hydraulic fracturing, to be successfully exploited at economic rate. This work focuses on unconventional gas shale reservoirs that are present worlwide. Nowadays, many efforts are ongoing in order to better understand their nature and the complex physical phenomena involved in the production, thus improving field development strategies. A fully integrated static and dynamic workflow for shale gas modeling was internally developed by eni. The aim was to deliver a more structured and business oriented technology to build a reliable and predictive model able to support and optimize management decisions in such complex systems (e.g. sweet spot definition, well positioning, completion, Both static and dynamic conventional workflows had to be tailored on unconventional context. In static simulation, differences are related to facies characterization and hydrocarbon volume in place calculation; dynamic simulation had to be adapted and improved to reproduce the hydraulic fracture explicitly, to model the frac fluid flowback, to consider gas desorption and multiscale fluid flow.