Gale Gustavson

Extended-range spectroscopic pH measurement using optimized mixtures of dyes.

The spectroscopic technique for pH measurement is a well-established laboratory technique that can give high-accuracy pH values. Recent studies have shown the advantage of this technique over standard potentiometric methods for pH measurements in fresh water and seawater and also at high temperatures and pressures. However, a limitation of the spectroscopic technique is that a single pH dye is sensitive only over a narrow pH range. We have developed optimized dye mixtures that are both sensitive and accurate over a broad pH range. The measurement is robust and simple, requires a minimum of two wavelengths, and is independent of the volume of the dye mixture added. Optimization of the dye mixture formulation to maximize accuracy in a broad range of pH involves varying both the dye type and its mole fraction and also accounting for spectral noise. This technique has been successfully applied for in situ pH measurements of oilfield formation waters.

Chain of custody for samples of live crude oil using visible-near-infrared spectroscopy.

In order to design oil production facilities and strategies, it is necessary to acquire crude oil samples from subsurface formations in oil wells in so-called openhole prior to production. In some environments, such as deepwater production of oil, decisions of huge economic importance are based on such samples. To date, there has been little quality control to verify that the crude oils collected in the sample bottles and analyzed up to a year later in the laboratory have any relation to the actual crude oils in the subsurface reservoirs. These high-pressure samples can undergo myriad deleterious alterations. Here, we introduce the chain-of-custody concept to the oilfield. The visible–near-infrared spectrum of the crude oil is measured in situ in the wellbore at the point of sample acquisition. This spectrum is compared with the spectrum measured on putatively the same fluid in the laboratory at the start of laboratory sample analysis. First, quantitative assessment is made of whether the fluid in the (high-pressure) sample bottle remains representative of formation fluids. Second, any specific changes in the spectrum of the fluid can be related to possible process control failures. Here, the entire process of chain of custody is proven. The chain of custody process can rapidly become routine in the petroleum industry, thereby significantly improving the reliability of any process that depends on fluid property determination.