0

0

1. How does asphaltene affect oil field operations?

Blocking pore space

①Solid asphaltene ②Asphaltene deposition in reservoir

③ Asphaltene problem in facilityDeposition in Separator

Feng et al., 2017 Plugging

Asphaltenes, which are often found in crude oil, precipitate due to changes in temperature, pressure and oil composition. The precipitated asphaltene particles grow to larger aggregates and are eventually deposited. The deposited asphaltene particles sometimes cause severe operational problems.In their natural form, asphaltenes are stably dispersed in crude oil. However, precipitation is triggered by several factors, particularly a decrease in resin content relative to asphaltene, and/or an increase in light components in case of gas injection EOR, etc. The precipitation/dissolution of asphaltene particles is theoretically a reversible process. However, in practice, asphaltene particles gradually aggregate and when these reach a certain size, the process becomes irreversible.

Emulsion Asphaltene deposition issues are encountered in all areas of oil field operations. Figure 1 shows solid asphaltene collected from production tubing. Asphaltene that sticks to the tubing wall and accumulates can block oil flow, resulting in production issues. Figure 2 shows a schematic image of asphaltene precipitation in an oil reservoir. Asphaltene particles that are adsorbed into the rock surface change the rock’s wettability and the rock becomes oil-wet. This ultimately causes a decrease in oil recovery. Furthermore, when the absorption becomes advanced, the pores, which provide a flow path, become blocked causing a reduction in permeability. Figure 3 shows asphaltene deposited in a production separator. The large-volume of asphaltene sludge occupies the bottom of the separator. This reduces oil/water separation efficiency and compromises the rate of operations of the entire production facility. In addition, it is well-known that asphaltene causes tight emulsion, which increases the residence time for oil-water separation. These issues contribute to the reduction in production rates to maintain sales-oil quality.

1.8m

1cm

1

Precipitation

Deposition

Asphaltene deposition process in crude oil

Settling

2. INPEX TRC’s approach to Prevent Asphaltene Problems

The figure shows asphaltene deposition by mixing an alkane solvent with crude oil. TRC’s Reservoir Properties Group studies the mechanism of asphaltene deposition to mitigate asphaltene issues at INPEX-operated oil fields. The group is also working on establishing a method of selecting effective asphaltene inhibitors. With regard to the issue of asphaltene-assisted emulsion, TRC has conducted research on the emulsion-forming mechanism, selecting an appropriate dispersant to help improve the efficiency of field operations.

To more accurately predict numerical simulations, TRC is currently conducting in-depth studies on the properties of asphaltene. To this end, TRC is incorporating new analytical methods such as molecular structure analysis and the Hansen-solubility parameter, and creating databases.

2

2. INPEX TRC’s initiatives on the prevention of asphaltene issues

(1) Conventional analyticsFlow Assurance System（FLASS）This apparatus is equipped with a Solid Detection System（SDS）to detect organic solid deposition and a High Pressure Microscope（HPM）to visually observe Asphaltene precipitation at onset conditions, identify the solid particles and monitor the change in their size and morphology in relation to temperature and pressure alterations. The amount of solids formed in the fluid sample when altering the pressure, temperature or composition of the fluid can also be determined using the HPHT organic solid filtration system. Example plots of a precipitating fluid are shown in the Figure below. In the SDS, laser light from a generator passes through fluid in a glass cell, and the laser power is measured by a detector. At first the laser power (as measured by the power meter) increases monotonically (almost linearly) as the pressure is dropped. The laser power drops due to asphaltene precipitate and the curve deviates from a straight line. The point corresponds to the onset pressure for solids precipitation. Measurement results are used as matching data for thermodynamic numerical modeling.

IATROSCAN

Flow Assurance System（FLASS）

IATROSCANThis apparatus can determine SARA (Saturate, Aromatic, Asphaltene and Resin) which is an important parameter for asphaltene risk assessment. Results are applied for Saturate / Aromatic vs Asphaltene / Resin plots which is known as a preliminary risk assessment of asphaltene issues. Results are also used for parameters of CPA-EOS to predict asphaltene precipitation conditions.

Asphaltene onset pressure

3

2. INPEX TRC’s initiatives on the prevention of asphaltene issues

(2) Introduction of new analytics

Hansen solubility parameterAs originally defined, asphaltene is soluble in Toluene and insoluble in n-alkanes. From this viewpoint, the Hansen solubility parameter (HSP) was introduced to understand the behavior of asphaltene. The concept of HSP is based on cohesive energy density indicating that the compatibility between similar molecules is high. According to the concept, when oil and asphaltene have similar HSPs, the asphaltene can be dissolved in the oil stably.

Hansen solubility of oil and its asphaltene (Image)

Rayleigh scattering methodRayleigh scattering is the scattering of light by particles much smaller than the wavelength of the light. The diameter of the particle is correlated to the wavelength of the scattered wave. By applying this property, we can evaluate the size of asphaltene particles found in oil with an asphaltene inhibitor (AI) and use the results to determine effective AIs.

Example of average molecular structure of asphaltene extracted from domestic crude oil

Asphaltene molecular structure analysisDetailed composition structure analysis, which has been widely developed in recent years, is applied to capture the essential features of asphaltene.The obtained asphaltene molecular structure will be used for molecular dynamics to render the results more realistic.

4

2. INPEX TRC’s initiatives on the prevention of asphaltene issues

(3) Evaluation methodology using digital technology

Appling Molecular Dynamics (MD)It is empirically known that produced water may

prevent asphaltene deposition when the water-cut ratio during oil production is high. The MD method is applied to understand this hypothesis. These computational simulations are researched in collaboration with higher education institutions.

Appling the Lattice Boltzmann Method (LBM)It is believed that precipitated asphaltene impedes oil flow through pore space, which causes a reduction in permeability. Although commercial reservoir simulators can mimic this phenomenon, results would not be highly accurate. To mimic this phenomenon with high accuracy, LBM was applied with a pore-scale model.These computational simulations are researched in collaboration with higher education institutions.

Investigation of effects of pore blockage using the Lattice Boltzmann method

1. How does asphaltene affect oil field operations?2. INPEX TRC’s approach to Prevent Asphaltene Problems2. INPEX TRC’s initiatives on the prevention of asphaltene issues�(1) Conventional analytics2. INPEX TRC’s initiatives on the prevention of asphaltene issues�(2) Introduction of new analytics2. INPEX TRC’s initiatives on the prevention of asphaltene issues�(3) Evaluation methodology using digital technology