Development and Application of an Asphaltene Deposition Tool (ADEPT) for Well Bores

Asphaltenes often tend to deposit in reservoirs, flow lines, separators, and other systems along production lines causing significant production loss due to restricted oil flow or damages caused to the units and instruments used along the flow lines. Asphaltenes are typically stable in the oil; however, changes in conditions such as temperature or pressure or compositional changes can trigger the phase separation and resultant deposition of these asphaltenes on the surfaces encountered along the flow. Hence, it is required to be able to forecast the possibility of precipitation of asphaltenes for given operating conditions and quantify the amount of deposition. In this work, the development of an asphaltene deposition tool (ADEPT) that can predict the occurrence and calculate the magnitude and profile of asphaltene deposition in a well bore is discussed. The simulator consists of a thermodynamic module and a deposition module. The thermodynamic module uses the Perturbed Chain Statistical Associating Fluid Theory (PC SAFT) equation of state to describe the phase behavior of oil, which is first characterized by using thermodynamic properties such as saturation points and asphaltene onset pressure data and physical properties such as the density of the oil. The deposition module is then used along with input from the thermodynamic module to calculate magnitude of asphaltene deposition along the length of well bore/pipe lines. The mathematical model used in the deposition module is first benchmarked and validated by comparing the simulation results against the experimentally measured asphaltene deposition flux in a capillary scale deposition experiment. The simulator was then used to study deposition in two field cases, for which measurements of asphaltene deposition profile were reported in the literature. This study demonstrates the development and application of a simple yet comprehensive simulator that can be easily integrated with other commercial flow simulators, facilitating quick calculations of the change in the asphaltene deposition profile and magnitude with change in operating conditions as the production continues. It is shown that the simulator enables operators to perform quick sensitivity studies and map out operating envelopes to avoid potential risk zones.