Asphaltene-deposition characteristics of a crude oil under high-pressure

Asphaltene deposition is a common and risky phenomenon during oil-reservoir development. In this study, two new high-temperature high-pressure-resistant experimental systems are constructed to measure the crude-oil asphaltene molecular aggregation condition (AGC), the asphaltene precipitation condition (APC) based on laser-transmittance technology, and the asphaltene deposition amount (ADA) via in-situ crude-oil filtration. Results show that the AGC pressure (PAGC) and APC pressure (PAPC) of a high-pressure crude oil (reservoir pressure of 133 MPa) are 88.9 and 78.3 MPa, respectively, at its reservoir temperature (407.15 K), which are much higher than its bubble pressure (27.9 MPa) and most PAPC values reported in the literature. This study is the first to report the PAGC values for crude oil. Both PAGC and PAPC increase with decreasing temperature. Additionally, the ADA of the crude oil is measured under six different conditions. At 407.15 K and 46.9 MPa, the ADA is 0.554 g/L, which increases with decreasing temperature and pressure. Additionally, a primary pressure range exists for the asphaltene deposition of crude oil. Finally, the main ingredient in the deposited sediments is asphaltene (exceeding 72 wt%), based on scanning electron microscope analysis and the analysis of saturates, aromatics, resins, and asphaltenes, with an H/C atom ratio of only approximately 1.1, thus demonstrating a high condensation degree.