Mechanical Properties of Drill Cuttings Based on Indentation Testing and Contact Mechanics Solutions

Abstract

Rock strength evaluation is commonly performed on extracted core samples. The retrieval process of core samples is costly and with high risk, especially in unconventional wells. Besides, mechanical testing carried out on core samples could be time-consuming, particularly for low permeability rocks such as shales. In contrast, tons of shale cuttings are generated and discarded at the end of drilling. Small scale testing, such as instrumented indentation test, could be performed on shale cuttings to obtain the mechanical properties of shale rocks. Unlike core samples, however, the bedding orientation, critical to the definition of mechanical properties of shale cuttings as transversely isotropic material, is indistinguishable on cuttings. A methodology has been developed in the following work to deduce the mechanical properties based on indentation testing of randomly oriented artificial shale cuttings. Estimation of shale cuttings' elastic constants was carried out using microindentation and constrained inverse algorithm developed based on contact mechanics solutions. Microindentation testing was performed on multiple oriented artificial shale cuttings to obtain the indentation modulus as the function of the unknown bedding orientation. The contact mechanics solutions for both transversely isotropic and anisotropic material were utilized to correlate the indentation modulus to the stiffness tensor components of transversely isotropic shale. An inverse problem was formulated with imposed constraints to identify the mean values of the quantities of interest that best fit the data. The constraints represent the physical information about the bounds on elastic properties as well as a mathematical constraint on the structure of elasticity tensor ensuring the accuracy and robustness of the solutions to this optimization problem. Lastly, Ultrasonic Pulse Velocity (UPV) test was performed to validate the modeling results and good agreement was found between the results of the experimental and modeling efforts and results from UPV tests performed on the same material. Mechanical properties of shale rocks hold great importance in the design and implementation of drilling and production programs. Retrieval of traditional core samples is known to be expensive and risky as a failure in the recovery process could lead to well abandonment. By using several cuttings with unknown varying bedding orientations, the elastic constants of shales were inferred based on the microindentation testing and the algorithm developed in this work. Successful implementation of this work would allow for a more efficient and economical mechanical characterization of shales.

Automated real-time formation evaluation from cuttings and drilling data analysis: State of the art

“…(1) Theory Recent advancements in small-scale testing enable mechanical testing on drill cuttings that can provide measurements from nanoscale (load < 100 mN) to microscale levels (load < 15 N) (Martogi et al, 2019;Shi et al, 2020;Alipour et al, 2021;Esatyana et al, 2021;Katende et al, 2021). Indentation measurements at the nanoscale-level enable acquiring mechanical properties of different constituent phases, and measurements at the microscale-level enable acquiring the bulk mechanical properties of the composite behavior of all constituent phases present at the nanoscale-level.…”

“…The two elastic mechanical properties obtained from the load vs. displacement (depth) plot shown in Fig. 6 that is referred as F (in place of P) in the provided derivation, and displacement is referred as h (Martogi et al, 2019).…”

“…A significant advancement in formation evaluation is the realtime analysis of drill cuttings, which are retrieved along with drilling fluids at the surface before passing through shakers/vibrating machines to separate the cuttings from the drilling fluids and may be analyzed to estimate parameters relevant to reservoir and completion quality. Typically, each well-drilling operation produces tons of drill cuttings that are discarded, reinjected into the subsurface, buried in-situ, or placed in landfills (Martogi et al, 2019). Drill cuttings are an abundant source of data that covers a larger stratigraphic section in comparison to cores, and its analysis in near real-time enables relatively economical characterization of reservoirs, such as characterization of mineralogy, petrophysical properties, mechanical properties.…”

Evaluation of geomechanical properties via scratch tests: Where are we and where do we go from here?

“…The uniaxial compressive test using load frame to evaluate the UCS of core plugs is one of the most popular methods. The indentation test [17] is another popular conventional method of estimating mechanical properties of rocks, and other materials. This method involves the use of a scratching tool to create indentations on the surface of the material surface.…”

Evaluation of rock mechanical properties via scratch testing and its impact on energy production: comprehensive review

“…The uniaxial compressive test using load frame to evaluate the UCS of core plugs is one of the most popular methods. The indentation test method is another popular conventional method of estimating mechanical properties of rocks [26], and other materials. This method involves the use of a scratching tool to create indentations on the surface of the material surface.…”