Geomechanical Sweet Spot Identification in Unconventional Resources Development

Abstract

Sweet spot identification in unconventional fields generally involves the identification of clusters and intensities of parameters that indicate the resource volume and production-related parameters, i.e., reservoir quality parameters such as total organic content (TOC), porosity, permeability, pay zone thickness, etc. The process usually incorporates interpretation of seismic data, well logs and other data to develop a 3D model that is used to suggest locations for productive wells. While understanding these parameters is essential in unconventional resource development, the potential to achieve productive hydraulic fractures, or the potential to exploit natural fractures, or the potential to achieve both simultaneously determines the feasibility of developing an unconventional resource. There are geomechanical conditions that are favourable to achieve the maximum productivity from stimulation operations. Identifying the geomechanical sweet spots within the field-wide reservoir quality sweet spots is, therefore, essential for optimum placement of wells and hydraulic fractures in unconventional reservoirs. This identification requirement is gaining more and more attention in the industry, which is helping the technique and workflow development. This paper discusses the workflow to identify the existence and properties of geomechanical sweet spots including rock mechanical properties and natural fracture distribution and how they help to decide the vertical location and direction of horizontal wells for optimal reservoir development. The workflow requires a multidisciplinary data set comprising drilling, geology, geophysics, production, geochemistry and geomechanical information. Based on detailed geological understanding, either a 1D or a 3D geomechanical model is built as the foundation for further analysis. Images, seismic data and structural information are the key to develop the understanding of natural fracture distribution. A discrete fracture network (DFN) model, or other definitive models, is required to identify stress-sensitive fracture distributions under different stress conditions. Due to the fact that local in-situ stress and natural fracture properties can be altered by production operations, initial unsweet spots may turn into sweet spots at some stage of production or injection operations. Based on the results of comprehensive geomechanical sweet spot analysis, an optimal development decision can be made based on integrated geomechanics, production and net present value analyses within the identified sweet spots. This paper includes results and illustrations from several case studies completed for a number of fields in the Asia Pacific to demonstrate the concept.