Micro-PVT Apparatus Without Mercury

Abstract

Summary. A new type of PVT apparatus is presented that avoids use of mercury and works with small sample quantities up to 10,500 psia [72 000 kPa] and 392F [200C]. The equipment is fully automated and the PVT cell is light enough to be weighed with an analytical balance within 10 (-5) lbm [0.5 × 10(-5) kg]. Efficient stirring inside the PVT cell is achieved by use of a magnet rotating in a magnetic field. Internal capacity of the PVT cell is varied by movement of a piston, the displacement of which is measured within 1 m to perform very accurate volume determinations. Introduction Measurement of volumetric properties is very important for designing industrial processese.g., those related to heat pumps, oil production, and to oil recovery. Previous industrial or academic volumetric techniques Previous industrial or academic volumetric techniques used variable-volume cells with mercury. Mercury is dangerous with respect to the operator's health. For this reason, variable-volume cells without mercury have been designed. To avoid the presence of mercury, some authors propose the use of bellows to compress the mixtures e.g., the cell form suggested by Martin and Bhada and Rousseaux et al. For industrial measurements, however, especially GOR studies, the equilibrium cells need very important internal volume controls that are not possible with bellows. Cells with internal pistons are more appropriate: the first apparatus was designed for oil PVT studies, the second apparatus was built to work on heat-pump fluids in temperatures and pressures up to 212F and 750 psia [100C and 500 kPa], and the third type 12 for use on gas/hydrocarbon systems (especially CO2/hydrocarbon systems) in temperatures and pressures up to 320F and 6,750 psi [160C and 45 540 kPa]. The main disadvantage of the equipment described in Ref. 10 is the length of time necessary for equilibration (it has no stirring device). In this paper, a new apparatus is presented for measuring GOR's of oil from the production presented for measuring GOR's of oil from the production well as a function of pressure. Because the cell is a blind type, measurements must be performed on one- or two-phase mixtures in the same way that classic PVT equipment measurements with mercury are made. This apparatus allows accurate measurements and is considered for use in a specialized laboratory rather than directly at a well location. In the last case, some equipment design simplifications would result in an apparatus that provides less accurate data, but makes experimental provides less accurate data, but makes experimental procedures faster and simpler. procedures faster and simpler. Experimental Procedure Principles and Equipment. A certain amount of mixture Principles and Equipment. A certain amount of mixture is introduced under pressure into the PVT cell that comprises a cell body and a piston. Then the PVT cell is thermoslatted. The volume occupied by the liquid mixture is measured from the piston position, and its mass is determined by an accurate weighing before and after its introduction. Density is obtained from these measurements. Then the internal volume is increased to create a vaporized fraction. The vapor is evacuated under constant pressure by decreasing the PVT internal volume. Volume is measured again and the total amount of vapor phase expanded at atmospheric pressure is determined (e.g., by use of a gasometer). Furthermore, samples of vapor are taken for composition analyses. Then the apparatus is ready to reach another lower pressure obtained by increasing internal PVT cell volume. This procedure may be repeated. The flow diagram of the equipment is represented in Fig. 1. The PVT cell is connected to a hydraulic press (HP in Fig. 1) and to the vapor outlet circuit through a regulating valve (RV). The outlet circuit comprises a cold trap (CT) to condense the heavy components, a sampling assembly (SA), and a gasometer (G). The PVT cell is surrounded by a two-envelope thermostatted jacket (TJ), where a liquid (thermoregulated by a liquid bath) is circulated. An electrical coil is wound around the external envelope to provide the major part of the thermal energy needed; the circulating liquid yields only the calories required for thermoregulation and avoids thermal gradients. Six solenoids are placed around the thermal jacket. They are powered in such a way that a rotating magnetic field can be created. This field drives a magnet (MA) attached at the top of the piston (P) in the PVT cell and permits efficient stirring of the mixture contained in the mixture compartment. The electronic hydraulic press supplied by ROP, Model DT 22421, allows regulation of either the pressure or the flow of the hydraulic liquid up to 10,500 pressure or the flow of the hydraulic liquid up to 10,500 psia [72 000 kPa]. Temperature is measured through psia [72 000 kPa]. Temperature is measured through thermocouples that are placed into wells machined into the body of the cell very close to the mixture. Thermocouples are calibrated with a platinum probe connected to a Mueller bridge. After calibration, temperatures are measured within 0.2F [0.1C]. SPEFE P. 85