The Scratch Test As A Means To Measure Strength of Sedimentary Rocks

Abstract

This paper was selded for presentation by an SPE Program Committee followng rwiw of tnfornubon contained in an abstract submitted by the author(s) Contents of the paper as t~. ham n'Jt~n rw-by the SccIety of Petroleum Engineers and are subject to w-on by the author(s) me material, as presented, does not necessarily reflect any Posmonof the =!ety of Petroleum Engineem, its officers, of membem Papers presented at SPE meetings are subject to publication fww by Edftorjal Committees of the~iety of Petroleum Engineers~ecbo"Ic reprodudon, distribution, or storage of any pa~of this paper for commercial pu~es without the w,tten tn"sent of the Soclefy of Petroleum Engineers is prohlbted PerrmssIon b reprcduce In PM is res~cted to an abstract of not more than 300 words, dtusbations may not be copied The abstract must mntaln conspicuous acknowledge. ment of Mere and by whom the paper ws presented Write Librarian, SPE, P O Box , Richardson, TX 7S0S3.%=, U S A, f~Of-972.952.9435 AbstractThe paper deals with an experimental method to assess the strength of sedimentary rocks. The testing procedure (a "scratch" test, or cutting test performed at a "small" depth of cut of typically 1 mm or less), the method of interpretation, and some experimental results are described, Experimental observations of rock cutting indicate that a "plastic" mechanism of failure takes place at small depth of cut d. This mode of cutting is also referred to as "scratching", The results of scratch experiments on various sedimentar ocks have indicated the possibility of estimating the rock strength from such tests. These experiments have shown that the force on the cutting face is proportional to the crosssectional area ,f of the groove (which is equal to u'd for a rectangular cutter of width IV)and that the intrinsic specific ener~&(the cocfflcicnt of proportionality between the cutting force component in the direction of cutter motion and A ) appears to be WC1lcorrelated with the uniaxial compressive strength q. Moreover, tests have shown that logs of rock strength arc possible; the force measurements have to be averaged typically over 1 cm. in order to produce logs ofs that are consistent and repeatable.The paper finally discusses the influcncc of the wear flat and the depth of cut on the results and also the limitations of the method,

A new approach to evaluate rock drillability of polycrystalline diamond compact bits using scratch test data

“…Based on Teale's theory of MSE, Detournay and Defourny (1992) developed a theoretical model for determining MSE using scratch test data and manifested that MSE of rock is approximately equal to its uniaxial compressive strength (UCS). Richard et al (1998) further demonstrated that the friction coefficient of a scratch test is equal to the intrinsic friction coefficient of the tested rock. Schei et al (2000) analyzed the force acting on a scratch cutter and found that there is a strong correlation between the hardness of rock and scratch measurements.…”

“…The key parameters of the experiment are shown in When the cutting depth is less than a threshold depth, the rock fails in a ductile mode; otherwise, it fails in a brittle model (see Figure 6). Under ductile failure mode, the cuttings are fine and uniform and generated in a continuous manner, and the cutting force is proportional to the energy consumed (Adachi et al, 1996;Almenara, 1992;Detournay and Defourny, 1992;Ghoshouni and Richard, 2008;Pei, 2012;Richard, 1999;Richard et al, 1998;Schei et al, 2000). MSE is closely related to inherent mechanical strength and drillability of rocks.…”

“…MSE of scratch tests Richard (1999) and Richard et al(1998) analyzed the stress acting on a cutter under plastic cutting mode in scratch tests. The normal of cutter face keeps at a constant angle h with respect to the horizontal cutting direction.…”

An Experimental Study to Reduce the Fracture Pressure of High Strength Rocks Using a Novel Thermochemical Fracturing Approach

“…The principle of the scratch test is to control and monitor the continuous shearing action induced by the motion of a 3 Geofluids diamond (PDC) cutting tool on the surface of a rock core sample [47,48]. The continuous high-resolution profile of rock strength (UCS) along the core sample is derived from the force acting on the cutter.…”

Modeling PDC cutter rock interaction

“…In his papers, The Methodology and the apparatus for performing a scratch test which was designed to measure the strength of the rocks were explained by Richard et al (1998). In this case a scratch test was the linear cutting of the rock by PDC bit with a constant cutting depth and constant speed.…”