Innovations in Geomechanics for use in Hydraulic Fracturing
Abstract Some elements in the current industry-accepted geomechanical workflow are fundamentally flawed, especially in complex lithologies. The current industry workflow simplifies the mechanical earth model needlessly and often to the point of absurdity. A common assumption is all formations are Continuous, Homogeneous, and Isotropic, and behave in a Linear Elastic manner (a CHILE formation). However, most formations are just the opposite, Discontinuous, Inhomogeneous (heterogeneous), and Anisotropic, and behave in a Non-linear Anelastic (not elastic) manner (a DIANA formation). Failure to account for DIANA behavior in formations, gives a totally incorrect vertical stress profile; and when used in conjunction with hydraulic fracture stimulations, gives incorrect fracture dimensions that leads to many of the problems facing oil companies that are developing unconventional reservoirs: inappropriate well, stage, and cluster spacing, devastating frac hits, and poorly preforming child wells.
I will present a new innovative workflow that diagnoses and differentiates DIANA from CHILE behavior allowing the geoscience specialist to choose rock physics and geomechanical models that are consistent with the individual layer’s mechanical properties and behavior. I will illustrate this workflow using an unconventional carbonate case study where the formation is highly layered, heterogeneous, and composed of sands, carbonates and shales. I found the minimum horizontal stress to be 0.1 psi/ft greater in the shales bounding the reservoir using this new workflow. In contrast to the CHILI model, the DIANA workflow showed substantial stress confinement that is consistent with microseismic and completion observations.
Geomechanical studies have had a large and positive influence on drilling and completion operations. However, to continue this success, the geomechanical analyst must acknowledge the fundamental flaws in the current industry-accepted workflow and use geomechanical models consistent with the formation’s behavior. The good news is this workflow does not require a new logging tool or more data. It does require a more complete and diligent approach using existing data.
Biography Tom Bratton is a consultant to the oil and gas industry specializing in geoscience applications for engineering operations. After retiring from a 36-year career with Schlumberger, he was a Visiting Professor and Research Associate in the Petroleum Engineering Department at Colorado School of Mines (CSM). While at CSM, he enrolled as a graduate student and earned his PhD in Geophysics. Before starting his consulting business, Tom was a scientific advisor to Schlumberger’s senior management, specializing in petrophysics, geophysics, and geomechanics with a broad base of experience in drilling, completion and reservoir engineering. Tom is a full member of the Society of Petroleum Engineers (SPE), Society of Petrophysicists and Well Log Analysts (SPWLA), Society of Exploration Geophysicists (SEG), European Association of Geoscientists and Engineers (EAGE), and the American Rock Mechanics Association (ARMA).