Determination of Asphaltene-Onset Pressure Using Multiple Techniques in Parallel

Abstract

Summary For accurate determination of asphaltene flow assurance, the importance of asphaltene-onset pressure (AOP) as direct information from live oil is undisputed. For this purpose, the standard has been to use a single-phase bottomhole sample, even though this is expensive. This fluid sample stores information most closely representing in-situ asphaltene conditions. Because of its costly collection, the handling and examination of such samples are conducted carefully to avoid inconclusive results and/or wastage; however, unexpected experimental difficulties sometimes result in the failure of AOP detection. In our AOP-measuring experience, the most modern method—laser light scattering (LLS)—has been applied because of its convenient and quick procedure. Our measuring equipment consists of a solid detection system (SDS) that uses LLS to determine AOP using the power-of-light-transmitted (PLT) function. In addition to the SDS, the apparatus also consists of other simultaneous measuring functions: high-pressure microscopy (HPM), which can be used to visually observe asphaltene particle count and size, and a densitometer and viscometer to investigate fluid kinetics. In this work, the HPM and viscometry measuring functions were demonstrated as useful supporting techniques to determine AOP in cases when SDS PLT results cannot be used alone. This work demonstrated that data acquisition should be maximized and as much information as possible should be obtained from the costly sample. AOP interpretation that is based on each type of data can be aligned in an order related to the asphaltene particle size and growth because the detection limits of each measurement are reflected in the AOP interpretation. In summary, comprehensive interpretation can achieve a higher-quality estimate of AOP: Different measurements give different interpretations that can be used in a synergistic manner.