This tutorial example aims to illustrate usage of continuum fracture modelling in ParaGeo by considering a representative element volume for a fractured reservoir of 10 x 10 x 10 m. A single set of vertical fractures perpendicular to the Y axis regularly spaced with a distance of 0.3 m is considered. The geometry is discretized in a single hexahedral element. Boundary conditions typical of Pore Volume Compressibility tests (PVC) performed on reservoir samples will be adopted.

 

PVC tests are uniaxial lab tests performed at reservoir stress conditions which aim to simulate the behaviour of the reservoir during a production/depletion cycle (and potentially injection). The experiment in performed under the following conditions:

•The vertical stress corresponding to the overburden weight is kept constant,

•Horizontal stress corresponding to reservoir conditions is initially applied and then displacements on the sides of the sample are fixed so the sample diameter is held constant

•Initial pore pressure of the reservoir is applied and then it is decreased to simulate drawdown due to production.

 

Under such conditions uniaxial compaction occurring on reservoirs during production can be replicated on the lab. Hence porosity and permeability reduction with pore pressure decrease will occur.

 

Arbitrarily chosen evolving pore pressure conditions will be applied to the whole element volume and coupling between geomechanical and fluid flow fields is considered.  A history point within the domain will be used to output evolution of the state variables (properties) during the simulation. Several cases with different material assumptions are described.

 

 

                       

Schematic of PVC test conditions (left) and geometry considered for the simulation (right)

 

 

Simulation Cases

 

Case 1a Poroelastic material

 

Case 1b Poro-elasto-plastic material (SR4)

 

Case 2a and 2b Case with 2 sets of fractures (poroelastic and SR4 plasticity material simulations respectively)