JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year PETROLEUM RESERVOIR STIMULATION Previous Question Paper (March - 2021 - R16)

Pertinent rock properties essential for reservoir stimulation include porosity, permeability, and mechanical properties such as Young's modulus and Poisson's ratio. Porosity represents the void space within the rock, typically measured using core analysis (Boyle's Law porosimeter) or well logging (density/neutron logs). Permeability defines the ability of the rock to transmit fluids, determined in the lab via steady-state or unsteady-state flow experiments on core plugs, or in-situ through pressure transient analysis (well testing). Mechanical properties dictate how the rock responds to hydraulic fracturing; these are measured in the laboratory using triaxial compression tests on core samples, where stress-strain relationships are analyzed to calculate elastic moduli.

In situ stress refers to the state of stress existing within the rock formation at depth, primarily composed of the vertical overburden stress and two horizontal stresses (minimum and maximum). It differs from atmospheric or lab-induced stress because it is constrained by the weight of the overlying rock column and tectonic forces acting over geological time, creating a non-isotropic stress field that dictates fracture propagation direction.

Determination methods include:

• Diagnostic Fracture Injection Tests (DFIT): A small volume of fluid is injected to create a micro-fracture, followed by a shut-in period to observe pressure decline, allowing for the calculation of the closure pressure, which approximates the minimum horizontal stress.
• Extended Leak-Off Tests (ELOT): Conducted during drilling to determine the formation fracture gradient.
• Acoustic Logging: Using sonic logs to measure compressional and shear wave velocities, which are then used to estimate dynamic elastic moduli and horizontal stress magnitudes through empirical correlations.