Patent ID: 6247358
Filing Date: 2001-06-19
Classification: E21B

Abstract:
A method for the evaluation of shale reactivity under constant pressure for a preserved shale sample collected from a formation reservoir, where the method attempts to replicate a set of downhole conditions experienced by said shale sample under either an equilibrium state or non-equilibrium state including extreme conditions as subjected to during duplicating a drilling operation done at an overbalance pressure, which comprises the steps of:collecting a set of downhole shale cores and preparing a corresponding set of test plugs for testing under conditions that model a state of original downhole hydration, such that a variable pore pressure across said shale cores can be controlled, adjusted or maintained by a pore pressure system;under the same conditions of original downhole hydration as maintained by application of a preserving mineral oil, introducing a test plug in a triaxial test machine for conducting a triaxial test via a pressurized test fluid and raising confining pressure in both axial and radial directions by increments of from 500 to 1,000 psi, while allowing a quiescent time period for equilibrating the sample after each increment in pressure, the pressure being raised up to the overburden pressure experienced by the collected shale in the reservoir;by draining, allowing the pore pressure to equilibrate between each increment in confining pressure, while still preserving conditions of original downhole hydration by circulating a preserving mineral oil through the pore pressure system, the equilibrium state being monitored by a triaxial detector apparatus sensitive to both radial and vertical strains;after equilibrium is attained, introducing the test fluid in the pore-pressure system to initiate a physical or chemical interaction with said shale sample so as to evaluate reactivity of the test plug of shale sample to said fluid by means of the interaction of the test fluid and the test plug while the test fluid displaces the mineral oil from the surface of the test plug, and monitoring said interaction of test plug and test fluid by means of performing and comparing a series of deformation measurements done on said shale sample subject to any of a set of different conditions including a temperature or thermal potential, a hydraulic potential and/or a chemical potential.