Natural fractures are important conduits for oil or gas flow to producing wells. Closure of these fractures seriously impairs well productivity. Determination of fracture conductivity and porosity versus closure stress are important for characterizing naturally fractured reservoirs and establishing safe operating conditions.
As the reservoir is depleted and the fluid pressure drops, the closure stress acting on the natural fracture increases and productivity declines because of the reduced fracture conductivity
Fracture Conductivity and Fracture Porosity Test Apparatus Fracture conductivities and porosities are measured on a core plug with a vertical fracture under uniaxial strain (zero radial strain) conditions.
Proppant Failure at Critical Closure Stress
Natural fractures are naturally propped open by formation materials in the form of sand grains. When drawdown pressure reaches a critical value, closure stress is strong enough to crush the proppant and close off the fracture.
Reservoir modeling techniques such as the Finite Element Analysis employed by Core Lab ProTechnics Business Unit use hard data from real-world rock mechanics testing to evaluate fracture conductivity and find the closure pressure for a system of multiple fractures.
Fracture Azimuth Knowledge of fracture azimuth is important for the placement of horizontal wells and for determining the optimum well locations in tight formations for drainage optimization and drive/sweep efficiency of water flooding or EOR. Sonic velocity anisotropy allows determination of the direction of optimum fracture azimuth with a field proven method (over 100 wells) that is inexpensive and reliable
Proppant Embedment Test
When naturally occurring proppant particles penetrate the walls of the fracture, the effective width of the fracture and thereby the fracture conductivity is decreased. Proppant embedment can reduce fracture width up to 60% with subsequent reduction of productivity from oil and gas wells.