Optimization of Reservoir Shrinkage Volumes:Laboratory And Field Results
Authors: Negenman T.J. , Thomas F.B. , Long Z.X. 
Published: March 2010

This paper reviews a technique to enhance the value of existing oil fields by optimizing the operating temperature and pressure of the surface processing facilities (batteries). Incremental value is added by reducing the shrinkage volume and density of the stock tank oil, which is offset to some extent by reduced gas production volumes and heat content. Improved laboratory equipment and procedures were assembled to model multi-stage separation systems. The experimental and theoretical results determined the optimum operating conditions and an economic evaluation was done which identified outstanding potential economic returns. A post mortem evaluation indicated that the project has performed as expected, with significant increases in both incremental cash flow and field value.

Introduction

With increasing economic pressures placed on the upstream oil industry, One must take advantage of every means possible to extract the greatest economic value from existing oil fields. One prospective means of doing so, where oil shrinkage volumes are reduced by modifying surface facility temperatures and pressures, may hold considerable promise. This method applies best to conventional and light oils with an API gravity of at least 35 °.

Background

An obvious method of increasing revenues from an oil-producing property is to maximize the sales liquid volumes and minimize the sales liquid density (while maintaining the appropriate RVP criterion) with respect to unit volume of reservoir fluid produced at the well head. The lighter the oil the more sensitive the oil's shrinkage response will be to the conditions chosen between the well head and the stock tank. For some oils the volume may only shrink by 1 % in travelling through the separator train to the stock tank. For lighter oils, however, the shrinkage may be more than 10 % and therefore considerable revenue could be realized if this shrinkage could be reduced. Figure 1 shows a typical separation train. For mature waterfloods and miscible floods, the conditions of the Inter Surge Vessel are usually determined by the volume of f1uids being produced since the temperature, in particular, is very difficult to change due to the large volume of water being produced and its relatively high heat capacity. Pressures are more easy to modify but their impact on volumes is usually less important than temperature. In combination, the two may act synergistically, however, resulting in considerable shrinkage changes.

FIGURE 1: Typical surface processing operations. (Available in full paper)

Two oil systems have been tested in the laboratory using specially designed equipment to measure accurate phase volumes. This will be reviewed in detail along with all the experimental data generated. The scheme was then implemented in the field and detailed economic analyses were performed to determine the impact on cash flow and field net present value.

Laboratory Testing

Figure 2 provides a schematic diagram of the pressure cells used most commonly to measure PVT behavior of petroleum fluids. The cell is a Ruska-type visual cell with an internal diameter of approximately 3.6 cm (1.4 inches) and a length of about 10 cm (4 inches).