Importance of Accurate Reservoir Fluid Characterization in Unconventional Offshore Resources and How Asphaltene Behavior Impacts Reserve Prediction

Abstract

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.

Enhanced Evaluation of Asphaltene-Related Oil Properties To Facilitate Production in a Complex Offshore Environment

“…1,2 It can have a severe impact on the economics of a project, by reducing its production capacity and increasing operating expenses (OPEX), and it can even impair the producible reserves of a reservoir. 3 Asphaltenes are stabilized under initial reservoir conditions, but they can become destabilized by changing pressure/ temperature conditions throughout the production life cycle. Mixing oils with incompatible fluids (e.g., aliphatic oils or condensates) can also have a detrimental effect on the asphaltene stability as well as acid stimulation treatments, gas injection (gas lift or floods), or high shear regimes.…”

“…Asphaltene deposition is a major problem in the oil and gas industry and can affect various parts of production systems. , It can have a severe impact on the economics of a project, by reducing its production capacity and increasing operating expenses (OPEX), and it can even impair the producible reserves of a reservoir …”