Mechanical Characterization of Grainstone and Dolomite Rock Samples from Quissamã Formation, Campos Basin

Abstract

Results from mechanical tests on grainstone and dolomite wellcore samples obtained from the Quissamã formation are presented. Unconfined compressive strength (UCS) logs obtained from scratch tests are compared to known relations. Elastic compressibility moduli, obtained from cyclic hydrostatic and oedometer compression tests, are compared to analytical formulation. Mohr-Coulomb strength envelopes are obtained from compressive tests, such as Brazilian tests, drained uniaxial compression and drained triaxial compression. The mechanical test campaign consisted of the following steps: 1) scratch test of three full wellcore sets from Quissamã formation to obtain UCS logs, 2) wholecore sampling for cylindrical rock plugging, 3) microtomography imaging of new cylindrical rock samples for internal structural integrity preview and 4) compression tests of plugged rock samples to obtain static elastic properties (Poisson's ratio, Young moduli, bulk moduli, grain compressibility moduli and oedometric compressibility moduli) and mechanical resistance properties (indirect tensile strength, drained UCS and drained confined compressive strength (CCS)). Experimental results were compared to literature UCS relations and analytical compressibility moduli formulation. It was possible to observe good concordance between UCS obtained from drained uniaxial compression tests and scratch testing profiles. Using the internal friction angle obtained from Mohr-Coulomb envelopes and the UCS results, it was possible to indirectly obtain an estimation of cohesion through Mohr-Coulomb criteria relations. Compressibility moduli obtained from experiments also were in good concordance with classical formulation for elastic deformation regime. In the end, the mechanical characterization campaign was succesful in obtaining resistance and elastic static properties for loading conditions and some unloading conditions.