PHASE III (2004-2007)

In Phase III (2004-2007) of the WAG project, we extended the work to coreflood experiments and performed a series of both 2-phase and 3-phase flow tests including WAG and SWAG. The measurements were mainly focused on a 1000 mD core of mixed-wettability using near-miscible fluids but also included some water-wet and immiscible experiments to form a basis for comparison. The majority of the tests were conducted with a very low gas-oil IFT of 0.04 mNm^-1 with some tests carried out at a higher gas-oil IFT of 3 mNm^-1 to determine the base case relative permeability curves.

In this phase we are continuing our study of WAG and SWAG processes, on low permeability cores, utilising the core facilities, simulation and mathematical modelling capabilities and the expertise available at Heriot-Watt University to further investigate the physics of the near miscible three-phase flow particularly in the WAG and SWAG processes for neutrally wet rocks. The study has two distinct and related parts:

1. High-pressure core experiments: Core test facilities capable of operating at simulated reservoir conditions to study three-phase flow, in-situ saturation measurements using x-ray and extensive fluid property measurements will be utilised to carry out WAG & SAWG tests.
2. Mathematical and Numerical Simulation: Simulators, comprising in-house fluid models and leading commercial simulators will be used to simulate and interpret experimental results. Experimental data will be used to evaluate the existing models and develop methodology for determining three phase relative permeability data for application in reservoir simulation.

The experience acquired in the process of WAG Phase 3 research, both on laboratory experiments and simulation will be very valuable in conducting the work in Phase 4.

Specific objectives include:

• To generate a comprehensive set of measured 2-phase and 3-phase relative permeability data.
• The data set would include measurements in two different cores under mixed-wet and natural water-wet conditions using a near-miscible gas-oil system.
• To evaluate the performance of the existing 3-phase relative permeability models against the in-house measurements.
• To develop a methodology to determine three-phase relative permeability data from the two-phase data applicable to mixed-wet rocks and near-miscibility conditions.
• To investigate the impact of interfacial tension, wettability, connate water saturation and petrophysical properties of the core on 3-phase relative permeability values and models.

PHASE IV (2008-2011)

Three-Phase kr Calculation

We have developed a Software that directly calculates and compares three-phase kr curves that can be obtained from a large number of three-phase kr models independently of any reservoir simulators. It also enables users to construct 2D tables of three-phase kr values, which can then be input to reservoir simulators (for models that are not available in the simulator). The software includes three-phase models, which are currently available in existing reservoir simulators as well as those, which are not currently available.

 

Three-Phase Coreflood Simulator

Three-phase kr and Pc curves are determined by matching the recovery and differential pressure obtained from three-phase displacement core tests. The program gives best estimates of three-phase relative permeability and capillary pressure based on suitable mathematical functions defined to describe their dependency to phase saturations. In this approach no assumptions are made regarding the dependency of the multiphase flow functions to a specific saturation.