The Automatic Differentiation General Purpose Research Simulator (AD-GPRS) is a flexible and extensible multiphysics simulation platform. It employs automatic differentiation to construct the Jacobian allowing for an easy extension to new physics and constitutive relations, as well as for complete flexibility in the specification of independent variables, which leads to a unified simulator for different formulations and solution strategies. There are no assumptions about the underlying grid structure thus unstructured grids are supported for accurate representation of the complex structure and heterogeneity of subsurface formations. Fully implicit or sequentially implicit time-discretization schemes are available. The latter is designed for handling different physical sub-problems with flexible coupling strategies. AD-GPRS can be used, for example, to simulate enhanced oil recovery (EOR) processes, CO2 sequestration in saline aquifers and depleted oil reservoirs, shale gas/oil production, and enhanced steam injection.

Currently, AD-GPRS consists of the following modules:

• Flow
  General component-based reservoir simulation tool. Several widely used variable formulations (natural and molar) and solution strategies are incorporated, including Black Oil, fully EoS (two- and three-phase, as well as support for external libraries), and K-value formulation.
• Thermal
  Adds support for thermal-compositional flows, for example, for simulation of steam injection or geothermal reservoirs.
• Geomechanics
  Simulates complex mechanical behavior including plastic deformation and thermal effects. Helps to understand physical processes for fractured and faulted reservoirs. Incorporates poro-elastic, thermo-elastic, and general poro-thermo-plastic models with complete flexibility in adding new constitutive relations. Can be used, for instance, for coupled simulations of gas production from a naturally fractured reservoir, steam-assisted gravity drainage (SAGD).
• Chemical reactions
  Capable of modeling kinetic and equilibrium reactions. Supports both natural and overall-composition variable formulations. Adds a key component for simulation of in-situ upgrading of oil-shale or CO2 sequestration in saline aquifers.
• Wells
  The wellbore flow and the near-well flow behavior have an important impact on well performance. Different techniques have been developed to model multiphase flow through the wellbore. We account for thermal and compositional effects. Currently supported well models include standard well, multi-segment well, and heater model.