CVD-CVE Device

While drilling through a reservoir, a lot of valuable information can be obtained from mud logging to support formation evaluation. Formation gas is considered as the first indication of a reservoir’s fluid characterization and reflects the extent of the productivity of the well. Geochemical ratios and equations can enhance the interpretation of field data and give the first indication of zones of interest that need further evaluation. The integration of the gas data along with the drilling parameters (ROP, ΔFlow) and geochemical features provide valuable information to quantify the rock properties such as porosity, permeability and identification of fractures while drilling. Since most of reservoirs display specific geochemical signatures in terms of types and quantities of hydrocarbon components and ratios between them, high quality gas data obtained from gas chromatography (GC) is potentially useful for reservoir evaluation and characterization.

The constant volume degasser (CVD) and constant volume extractor (CVE) are the systems able to extract a gas sample from a constant volume of mud regardless of the drilling fluid flow rate and the variations in the mud level. Generally, CVD and CVE instruments are used for analysis of C1-C5 and C5-C10 hydrocarbons, respectively. The CVE, which is also called heated constant volume trap (CVT), regulates the temperature of mud as it flows continuously from the return flowline through a specialized mud-sampling device.

The working principle is based on the suction of a certain volume of mud per minute using a pump. The amount of gas sample extracted from the mud is influenced only by the downhole conditions, since the volume of mud centrifuged is constant. The gas extracted merges with air in the upper part of the bowl and then a pump forces it out with a constant flow rate to the gas distribution system (GDS). From the GDS the gas flow is distributed with constant flow rates to the different gas detectors. The gas readings are monitored by a complex system which provides real-time continuous measurements of the concentration of formation gases from very light components (C1-C5) such as methane, to heavy components (C5+) such as n-hexane.