Reservoir fluids are a complex hydrocarbon system that passes unique compositional stages when pressure and temperature change. Proper collection and accurate evaluation of a representative reservoir fluid sample during the exploration phase is one of the first crucial steps describing the chemical and physical nature of the hydrocarbon mixture. Understanding the importance of having a proper fluid characterization from the beginning of the development stage gets particularly essential in context of asphaltene precipitation and potential damage in unconventional reservoirs. Even in conventional reservoirs, formation damage caused by asphaltene deposition can have a severe impact on oil production and the prediction of remaining recoverable hydrocarbons in place. Multiple fraccing of unconventional tight oil reservoirs, conducted to produce economically despite low permeabilities, enhances the effect of uncertainty in reserve estimation. Precipitated asphaltenes potentially pjlug small pore throat channels in the near wellbore zone whereas high permeable fractures connect a wide area deep into the reservoir. Possibilities to maintain the reservoir pressure, e.g. water injection, are often limited due to the low permeability, consequently making it hardly manageable to stay above the asphaltene onset pressure in tight oil reservoirs. Having a firm understanding of the reservoir fluid and the asphaltene properties helps to reduce unexpected occurrences during production and later field life as well as predicting remaining recoverable reserves in place. This paper describes the fluid characterization of unconventional resources in a complex offshore environment and the effort undertaken to get a proper understanding about the hydrocarbon fluid phase. Challenging interpretations of conducted experiments about the asphaltene nature have been intensively studied to support forthcoming decisions in the field development process. Furthermore, the outcome of those analyses has led to a detailed investigation about the impact of asphaltene behavior in tight oil reservoir formation and the impact in prediction of remaining recoverable hydrocarbons.

Asphaltene destabilization is a widespread problem in the oil industry. Under initial pressure and temperature conditions in the oil reservoir, asphaltenes are stabilized by building micelle structures in which they are associated with resin and aromatic compounds. Stable asphaltenes do not pose problems during oil production; however, if pressure/temperature conditions change throughout the production system, asphaltenes might become destabilized. Once destabilized, asphaltenes can potentially impair the whole production system. The development and implementation of a profound chemical injection strategy to mitigate asphaltene-related problems are paramount for a successful and sustainable fluid production if routine operating conditions are within the asphaltene instability range. A preventive asphaltene mitigation strategy is generally preferred; i.e., it is beneficial to avoid the occurrence of asphaltene-related problems in the first instance, instead of applying any remediation method afterward. Boundary conditions defined by the oil characteristics and the actual production conditions can make the development of a completely preventive chemical treatment strategy challenging. This applies especially in the offshore sector of the industry with given limitations in accessibility to the production and storage facilities accompanied by stringent regulatory requirements. This paper describes the analysis of a crude oil produced in a complex offshore environment, including mixing with condensate and storage in a gravity-based subsea tank. It highlights the asphaltene-related characteristics and compares different technologies to assess stability of the oil in neat form and upon mixing with condensate. The impact of different asphaltene inhibitors/dispersants on the oil has been investigated, and additionally, the effectiveness of dissolver chemicals on artificially sedimented asphaltene deposits has been evaluated. Different lab experiments have been conducted to determine the asphaltene concentration in the fluid and sediment layer over time with the aim to quantify the sedimentation. Computational fluid dynamics (CFD) was used to simulate potential sedimentation phenomena. This paper is based on a presentation given at the 19th International Conference on Petroleum Phase Behavior and Fouling (Petrophase 2018) in Park City, UT, U.S.A. Names of the platforms, distinct locations, and actual production numbers are not revealed in the paper with respect to information protection requirements of the parties involved.