One of the largest problems facing the oil industry today is to characterize fluid and architectural complexities of oil reservoirs. This applies particularly in the development of offshore fields where reservoir reconnaissance is impeded by the high costs of wells, often exceeding $100 million. As such, new methods are being developed to address these complexities. Downhole fluid analysis (DFA) is a new method of in-situ fluid characterization used to understand the heterogeneous distributions of hydrocarbon fluids in the reservoir and to identify which crude oils merit subsequent analysis in the laboratory. Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful new method to analyze complex hydrocarbon mixtures such as crude oils and, especially when combined with mass spectroscopy, to elucidate explicit chemical structures. Here, we explore the protocol of DFA coupled with GC×GC to address reservoir complexities.
Accurate measurement of pH is important in several diverse fields, such as process control, reaction equilibrium and kinetics, environmental research to monitor seawater chemistry and natural water quality, biomedical research and in oilfields. The International Union of Pure and Applied Chemistry (IUPAC) has issued guidelines for the standard potentiometric technique for pH measurements. These methods and calibrating standards are, however, recommended only for 278 -323°K, 0.101325 MPa and ionic strengths below 0.1 mol/kg water. 1 The reasons for these measurement constraints are the uncertainty in liquid junction potential and reference electrode stability at high temperatures, pressures and ionic strength and the lack of calibrating standards. Many chemical reactions and processes require pH monitoring and control at extreme conditions of pressure, temperature and salinity. In oilfield applications, accurate pH measurements require that they be made at downhole wellbore conditions with fluids in their native state at high temperatures (typically 323-473°K), high pressures (typically 30 to 100 MPa), and high ionic strengths (typically 0.5-5 mol/kg water). pH is a key parameter whose accurate measurement at downhole wellbore conditions is critical in understanding formation fluid water chemistry to predict corrosion and scale potential in well tubing and surface facilities.Spectroscopic measurement of pH with very high accuracy using pH-sensitive dyes is a well-established laboratory technique for ambient conditions since the early 1900's. 2,3 More recently, this technique has been shown to improve precision for seawater pH measurements. 4 Using equimolal tris buffers for total pH scales, dye equilibrium dissociation constant was characterized at 0.101325 MPa pressure as a function of temperature (293°K to 303°K) and salinity over the narrow salinity range characteristic of seawater (30 to 37 salinity range corresponding to ionic strengths of ϳ0.53 to 0.66 mol/kg water). Yao and Byrne 5 have also applied this technique for freshwater pH measurements, where potentiometric methods can prove to be problematic. Using phosphate buffers, the dye equilibrium
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