Fiber Optics for Sub-Surface Strain Forecasting

Summary Sub-Surface Strain Forecasting (SSSF) is typically derived from Mechanical Earth Models (MEM). A MEM represents the mechanical properties of rocks, including elastic moduli, fractures, stresses, temperatures and pressure conditions. MEM calibration and verification is an imperative part of the SSSF process. A typical MEM calibration process comprises modifying the model boundary conditions, the regional tectonic displacement field, or material properties to best fit observed data. Fiber optic interrogation presents an opportunity for efficient direct and indirect strain measurement for MEM calibration and verification. Key is regular monitoring of displacements with fit for purpose resolution for attribution to different rock layers. This paper shows how down-hole fiber is to be used for monitoring low levels of overburden strain in an on-shore oil field. A staged pilot over 3 years has been designed to progressively test suitability of different monitoring systems including use of Vertical Seismic Profiles (VSP’s), Surface Orbital Vibrator (SOV), behind casing fiber and clamped to tubing fiber for direct and indirect strain measurement. Multiple types of fiber sensing are to be used, including Distributive Acoustic Sensing (DAS), Distributive Strain Sensing (DSS) and Distributive Temperature Sensing (DTS).