SCORPIO – A Chemical Treatment Reservoir Simulation Program

Ian Hawkyard is Associate Consultant with ECL Technology Ltd (http:/www.ecltechnology.com). Here he outlines the features of SCORPIO a chemical treatment IOR processes simulator. SCORPIO’s capabilities are available through the reservoir engineering consultancy services offered by ECL Technology - please contact Maggie Thompson (Maggie.Thompson@ecltechnology.com).

SCORPIO is a general purpose, three-dimensional multi-phase, multi-component, finite difference reservoir simulator. It has particular application to modelling chemical treatment IOR processes, although its capabilities allow it to be used to study other processes such as hot water flooding, scale inhibition and reservoir souring. It has been used extensively in a wide range of applications including full field simulations, IOR pilot studies, evaluation of single well treatments and design/interpretation of laboratory experiments.

SCORPIO’s highly flexible reaction and equilibrium phase packages form the basis of the mechanisms by which polymer flooding and in-situ gelation may be modelled. The simulator allows for partitioning of the trace components, such as polymers, between the oil and water phases, and between the mobile phase and the reservoir rock. One example of SCORPIO’s application to polymer modelling is a case where a novel recovery mechanism for polymer flooding in gravity dominated viscous oil reservoirs was identified, as described in SPE paper 27772 (Reference 1). Another paper, SPE 20242 (Reference 2), gives an example of SCORPIO’s gel modelling application. In this case sensitivities to various degrees of vertical communication within heterogeneous formations, and the effects of different gel strategies, were investigated using a single well model.

The Figure 1 is taken from a SCORPIO study which looked at in-depth blocking to boost late life reserves and illustrates the placement of a mobility reducing agent (polymer or gel) in the simulation grid at the end of the simulation. The figure shows that the system has been successful designed to selectively reduce the mobility in the high permeability (upper) zone, making full use of SCORPIO’s modelling capabilities described below.

Figure 1: 3D model showing selective blocking in high permeability (upper) zone

Equilibrium partitioning and adsorption of trace components are handled through the phase package resulting in all components co-existing in an equilibrium state according to user defined isotherms. The isotherms may have complex interdependencies on other component concentrations and temperature. Provision for such interdependencies is available in most of the chemical and physical processes modelled in SCORPIO. This is the key to its versatility, allowing data derived from experimental results as well as from analytical models to be utilised, rather than being constrained to use only hard-wired internal formulae. For example, in modelling polymer adsorption, as well as provision of Langmuir isotherm models, a fully flexible tabular input may be used to construct an isotherm (or to define dependencies of the Langmuir coefficients). Both reversible and irreversible adsorption may be modelled using the phase package.

The kinetic equivalents of the equilibrium partitioning and reversible/irreversible adsorption are modelled within SCORPIO’s reaction package. Kinetic adsorption is defined through a set of adsorption “sites” allowing the same component to adsorb at different rates or via different mechanisms (e.g. reversibly and irreversibly) at different sites on the rock. For kinetic partitioning and Langmuir adsorption, the kinetic model can be allowed to automatically switch to the equilibrium model at rates which become very fast compared to fluid flux within the model.

SCORPIO’s phase and transport property models allow the effect of polymers on phase viscosity (including temperature dependence and shear-thinning effects) and phase resistance factors (permeability reduction effects) to be modelled in an extremely flexible manner. The reduced pore space accessible to polymer molecules may also be modelled. Degradation of the polymer over time is handled through the reaction package.

In addition to modelling kinetic adsorption and degradation of components such as polymers, the reaction package is flexible enough to allow reactions amongst components within mobile phases or between mobile phases and adsorbed material. In this way it is possible to model in-situ gelation. This can be achieved by a boundless variety of methods ranging from defining a single reaction between a polymer and a cross-linker component, through to very complex processes such as those where the gel is built up in layers on the rock, involving definition of several components and reactions.

Reaction rate may depend on component concentrations and adsorption levels, temperature and shear rate. This may be achieved through tabular input or by simple power-law based formulae. A link between the reaction package and the equilibrium phase package permits modelling of reactions where the reaction rate is near instantaneous, dependent only on limiting “threshold” concentrations and temperatures.

The effect of injecting surfactants to reduce the interfacial tension (IFT) between the oil and water phases may be modelled in two ways. The simplest of these is using the two phase oil-water phase model via interfacial tension tables. However, SCORPIO’s quaternary phase package permits the modelling of four component oil, water, surfactant and co-surfactant system in which a third, “micellar”, phase may exist. The phase behaviour in this case is described in terms of a series of pseudo ternary slices through quaternary space with the four components partitioned into the three phases. Additional components (tracers, polymers etc.) then partition between the water and oil “pseudo-components”.

With either surfactant model, a capillary number dependency in the relative permeability tables allows oil-water relative permeabilities to tend to straight lines as the IFT is reduced.

If the quaternary phase package is not used, the third phase can be utilised to model a simplistic gas phase. This also allows SCORPIO to be used for foam modelling.

• SG Goodyear, BJ Mead, CL Woods, "A Novel Recovery Mechanism for Polymer Flooding in Gravity Dominated Viscous Oil Reservoirs, SPE RE, November 1995 (SPE 27772)
• DS Hughes, CL Woods, HJ Crofts, RT Dixon, "Numerical Simulation of Single-Well Polymer Gel Treatments in Heterogeneous Formations", SPE/DOE Sixth Symposium on EOR, Tulsa, OK, USA, April 1990 (SPE 20242)

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