Ridgeway Kite has built on its extensive experience in reservoir simulation solver techniques, and coupled this with the latest massively parallel computing systems to develop the 6X simulator. The resultant solution speed of 6X enables it to be adapted to more compute-intensive problems, specifically, to the implicitly coupled treatment of flow dynamics and geomechanics prevalent in the modeling of unconventional resources. This delivers a unique platform for unconventional field development planning, completion design and recovery management.
The full coupling of Geomechanical rock properties with the reservoir model allows the geomechanics of the reservoir to determine the shape, extent and conductive properties of each fracture stage, in each well, and the effect that fracturing has on existing or planned nearby wells.
Fractures – The image shows an example of the complexity generated by the rock breaking during hydraulic fracturing, showing both tensile & shear fractures.
The simulator models the life cycle of multi-well sections, from the fracturing of the first well, through to the end of production of the last well. It accounts for fracture generation, closure and well interference.
Calibrated models can be used to investigate the effects of well spacing, well timing, stage length, cluster spacing, job size, infill well location and design. These well plans can be further optimized using the integrated multiple realization capability in the simulator.
Optimizing well spacing – The image shows the interference between wells.
The 6X simulator has been designed to model unconventional oil and gas reservoirs. It includes features that have been developed for the CDOT (Completion Design and Optimization Tool) project with industry partners.
Through the project the simulator has acquired unique capabilities to help model the physics of unconventional reservoirs, including multi-porosity systems and vapor-liquid equilibrium in confined media. It includes advanced capabilities to help in modeling fracture mechanics above and beyond those found in other simulators and similar tools.
6X has multi-porosity capabilities, in which different porosity systems (e.g. fractures, kerogen, sandstone) can be arbitrarily connected in a hierarchical model. They can be connected directly, in serial, or more generally as seen in the image above.
Multi Porosity – Illustration shows the variety of matrix-fracture connections possible in the simulator
The model can account for the dual porosity systems commonly modeled with other simulators, with full elimination of the matrix equations for efficiency. A mixed single/dual porosity capability can also be handled.
The presence of high capillary forces in very small pores in unconventional reservoirs results in suppression of the bubble point pressure. To correctly model this, 6X solves the vapor-liquid equilibrium problem consistent with capillary pressures to make this correction.
Stress Dependent Permeabilities
Fracturing events are captured in 6X using regional tables of permeability modifiers versus net stress, which are applied dynamically to modify the reservoir flows. The table modifiers are either applied directly, or conditionally using a Mohr-Coulomb model and an input stress field. Several hysteresis models are also available to model the closing of fractures.
In addition, special consideration is given to the effects on well PIs and flows between different porosity systems, and provision is made to model background effects in nearby zones with transmissibility compressibilities.
Gels and Proppants
The 6X simulator has a tracer capability in which extra fluid components are carried around with the reservoir fluids, but which do not on their own affect the flow solution. They can be used as markers, to trace the flow of injected or initially in-place fluids through the reservoir throughout a simulation run.
6X uses the tracer facility in unconventionals for modeling the effects on flow of gels and proppants. Gels and gel breaker properties can be specified and their combined effect on fluid viscosity modulated. Proppant density can also be accounted for, with special consideration given to the prevention of ingress into non-fracture matrix, and to the differential flow of proppant in a fluid due to the effects of gravity.
Proppant – Example above with a cropped model displaying density of trapped proppant in a model (highest values in red).
Rock compaction models include a standard rock compressibility input, or tables of compressibility versus net stress, including hysteresis effects.