In situ bubble point measurement using spectroscopy

Develop and research a new downhole bubble point pressure measurement technology suitable for black oil and volatile oil to enhance well analysis using spectroscopy.

Representative fluid characteristics are required for a wide range of oilfield lifespans, such as the initial scale and production planning of reservoir hydrocarbon reserves. Fluid characteristics are usually obtained from laboratory sample analysis, but some fluid characteristics can also be measured in situ using formation testers. A new downhole bubble point technology has been developed to supplement traditional well analysis measurements. Measure the initial pressure of bubbles on reservoir fluids for early estimation and sample representativeness.

The method outlined consists of two parts: bubble generation and bubble point pressure detection. After separating a certain volume of uncontaminated fluid in the fluid analyzer module of the formation tester, use a downhole pump to reduce the streamline pressure at a low and accurate flow rate. Use spectral measurements at a data sampling rate of 128 ms to detect bubble initiation. Even very small bubbles can scatter visible and near-infrared light passing through the pipeline, ensuring the detection of bubble formation. The streamline pressure reduction experiment can be conducted within a few minutes, at any time, on a series of well bodies.

Underground bubble point pressure measurements were conducted on four different fluids. The gas/oil ratio range for testing fluids is 90 m3/m3 to 250 m3/m3. In each case, the downhole bubble points obtained from the streamline decompression experiment match the saturation determined by constant component expansion in the laboratory, reaching within 350 kPa. Firstly, use near-infrared spectroscopy to detect the initiation of bubbles. As the pressure decreases, the size of bubbles coming out of the solution will increase, and the presence of bubbles can be recognized by other downhole sensors, such as live density and fluorescence, manifested as signal scattering. For each fluid studied, the pressure and density measurements obtained when the streamline pressure is higher than the saturation pressure are also used to calculate the compressibility of pressure changes with pressure.

This type of downhole bubble point pressure measurement can optimize real-time sampling operations, achieve fluid classification and separation research, and can be used for early elucidation of fluid state equation models. This technology is suitable for black oil and volatile oil. For heavy oil with very low gas content, the accuracy of this technology may be reduced due to the energy required to overcome nucleation barriers.

Previously recorded techniques typically infer downhole bubble points by analyzing the rate of change in streamline pressure. For the first time, it demonstrated the beginning of directly detecting the appearance of bubbles without the need for additional specialized downhole equipment, and was validated based on laboratory measurement results. The measurement accuracy was achieved by combining a 128 millisecond spectrum with a low and accurate decompression rate.

Source: Laser Net