Reservoir Fluid Properties Measured Downhole

Abstract

Technology Update Over the years, oil companies have started recognizing that a disturbing number of reservoir- and production-management problems could be traced back to a single root cause—inadequate understanding of reservoir fluid properties. After performing detailed analyses and calculations, scientists and engineers were able to quantify the cumulative economic effect of these shortcomings in reservoir knowledge. This provided encouragement to pursue a solution, but the process was difficult. Although it may seem obvious, a prerequisite to accurate reservoir fluid analysis is the ability to acquire a representative sample of downhole fluids. In the late 1980s, a promising piece of the puzzle was developed—a pumpout module that could be incorporated in modular formation-dynamics testing tools. Until this time, highly contaminated fluid samples had been the norm because previous formation-testing tools were a closed system, whereby invaded mud filtrate was produced into a segregated sample chamber before an unknown quantity of formation fluid could be sampled. The pumpout module enabled the field engineer to pump undesirable fluids from the formation—via the sample probe—directly into the borehole, ensuring sample acquisition was performed after the produced fluid had been cleaned up to lower levels of contamination. However, a breakthrough came in 2006 with the introduction of a focused probe tool that consistently provided a formation fluid sample virtually free of contamination from the invaded drilling mud filtrate. By using dual pumps to withdraw both the reservoir fluid and the surrounding mud filtrate simultaneously into separate flowlines, the mud filtrate could be diverted into the borehole, while the relatively pure stream of formation fluid could be obtained for measurement and collection by the field engineer in real time. Variety of In-Situ Measurements Enabled Once it became possible to acquire a pure sample, representative of formation fluid in reasonable time under downhole conditions, a variety of real-time measurements became feasible. Advanced instrumentation was packaged by Schlumberger into its modular formation-dynamics testing tool to perform nine separate field-selectable measurements, characterizing and describing produced fluid to enable real-time downhole analysis. The technology package, called the InSitu Fluid Analyzer system, can measureHydrocarbon fluid composition (C1, C2, C3–5, C6+)Reservoir fluid gas/oil ratio (GOR)Reservoir fluid CO2Reservoir fluid densityReservoir fluid viscosityReservoir fluid pHReservoir fluid colorReservoir fluid fluorescenceReservoir fluid resistivity