Flashing of reservoir liquids and their associated PVT behavior is critical for many oil field operations. Conventional PVT work considers only the reservoir oil and its gas flash behavior. The presence of a water phase in the reservoir is normally neglected. It is assumed that water does not flash below its boiling point. This assumption is justified to some degree if the system contains no components which are soluble both in the water and oil such as CO2 and other gases. Most reservoir fluids contain such gases. Therefore, the conventional bubble point considerations as used for field operations are conceptually wrong. Using only two-phase PVT data in petroleum operations when in reality a three-phase system exists in the field as commonly done could conceivably generate various problems related not only to the proper reservoir management but also to handling of carbonate or sulfide scale problems.

The experimental data on (a) three-phase PVT work and (b) CO2 partitioning effects between oil and water under various conditions are discussed. Actual and different oil/water/gas systems from three California reservoirs were examined.

The results of this work show that the three-phase PVT data are extremely important under the following field conditions:

  1. The WOR is varying and high.

  2. The GOR is varying and high.

  3. The concentration of CO2 and/or other gases which can dissolve in both oil and water phases is high.

  4. The water breakthrough occurs in a waterflooded reservoir.

  5. During CO2 flood operations.

  6. A carbonate or sulfide scale problem exists anywhere in the field.

  7. Application of inhibitors to prevent the formation of various types of scale.

In principle, the phase behavior of reservoir and/or produced fluids as well as.the associated CO2 partitioning effects between the various phases depend upon the following variables:

  1. Pressure and pressure changes.

  2. Temperature and temperature changes.

  3. CO2 concentration in any of the three fluid phases potentially existing in the reservoir prior and anywhere in the system, during and after flashing of the reservoir fluids.

  4. Composition of reservoir brine (including pH), oil and gas.

  5. WOP, GOR and GWE under any set of pressure and temperature conditions.

The present paper discusses the importance of three-phase PVT data (including bubble point and flash behavior in the presence of CO2) and CO2 partitioning data for oilfield operations. Sampling, testing and computational procedures are described. All the discussions are supported through three-phase PVT data generated in the laboratory for three different types of reservoir fluids from California fields.

Keywords:
production control, pvt cell, pvt measurement, oil phase, reservoir, experiment, water phase, sample container, liquid phase, three-phase system
Subjects:
Well & Reservoir Surveillance and Monitoring, Fluid Characterization, Phase behavior and PVT measurements
Copyright 1987, Society of Petroleum Engineers
You can access this article if you purchase or spend a download.