Introduction

The presence of mechanical heterogeneity under the well log resolution is commonplace in unconventional plays and can deeply impact geomechanical assessments ranging from wellbore integrity to completion design. Thin (<1 inch in thickness) discrete layers may locally exhibit order of magnitude contrast in stiffness and strength relative to the surrounding material. Depending on stress magnitude and orientation, relatively weak or strong layers may lead to unexpected failure, mechanical decoupling between adjacent blocks, and complicate the understanding of fracture propagation by causing additional energy dissipation.

To validate these potential adverse effects, a thorough screening was conducted using a petrophysical scanner on sections of core recovered from the Permian Basin,Vaca Muerta unconventional formation and deep GOM sandstones and shales. The petrophysical scanner was sequentially run with the following probes: Vp and Vs to provide geophysical information, a geomechanical probe named the Impulse Hammer, and an FTIR (Fourier Transform Infrared Spectroscopy) probe to provide mineralogical information, all at the same indexed locations along a vertical profile with a 5 mm spacing.

Method and Examples

New England Research's Core AutoScan (Figure 1) is a unique measurement platform developed for the detailed quantitative and efficient description of core properties. It is capable of scanning slabbed and whole core or plugs for gas permeability, resistivity, ultrasonic compressional- and shear-wave velocities, composition, mechanical strength, and elastic stiffness (Impulse Hammer) at the mm scale.

The Impulse Hammer was originally developed to provide a non-destructive method to measure the mechanical profile along a core. The Impulse Hammer captures the physics of the impact by measuring the force-time function at the indenter - a small instrumented sensor is free falling onto the core surface from a preset height. Two independent parameters can be extracted, a reduced Young's modulus and an impulse hardness. The spatial resolution of a single measurement is of the order of 2 mm and the footprint is comparable to that of a micro-indentation test. An example of a representative data set is shown in Figure 2.

Conclusions

The combination of fast and non-destructive physical property measurement platorm with workflows capable of relating these measurements across scales is a powerful tool at all stages of field life from exploration and development to production.

Biographical Sketch

Ramil S. Ahmadov is a principal geoscientist at New England Research. He is an integrated scientist with experience in conducting pure and applied research in the area of geoscience and engineering who has held various roles at BP, Ikon Science and New England Research. Dr. Ahmadov has considerable experience integrating laboratory, well log, seismic and production data within integrated multidisciplinary teams at all stages from exploration and development to production. Ramil holds PhD and MS degrees in geophysics and geology from Stanford University and BS and MS degrees in petroleum engineering from Azerbaijan State Oil Academy and University of Wyoming, respectively.

Gregory Boitnott is a principal scientist with New England Research, Inc. since 1992, and NER vice president since 2005. He is a designer of the AutoScan and AutoLab systems at NER and is the inventor of NER's patented method for estimating pore structure of earth formations from their petrophysical properties. Boitnott combines laboratory and theoretical studies of fundamental rock properties and studies their relationship to the microstructural variables that control them. His work has resulted in the development of new testing methods and data mining software used for quantitative model building. His current research involves building physical models of heterogeneous and anisotorpic rocks and sediments at the millimeter to meter scale. Boitnott's work is used by NER to understand the implications of heterogeneity in rock physical properties to assist clients in the areas of reservoir engineering, petrophysics and geophysics. Greg holds MS and PhD degrees in geophysics from Columbia University.