Page 276 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Formation Damage by Organic Deposition 247

time at which there will be significant loss of productivity and permeability
in the near wellbore region. This essentially means optimal time for
remedial actions.

6.1.5 Experimental techniques to determine asphaltene-
onset-pressure and wax-appearance-temperature
Fluid samples are obtained for asphaltene-onset-pressure (AOP) and wax-
appearance-temperature (WAT) measurements. The samples are kept
above reservoir pressure at all times to prevent reversibility of asphaltene
precipitation, because they aggregate within an observed range of the
bubble point value. When pressure drops from reservoir pressure during
production, the density change causes a corresponding solubility change,
which tends to trigger asphaltene precipitation, with the most precipita-
tion happening close to bubble point pressure.
The AOP test is performed in a high pressure visual cell. The solid-
deposition-system (SDS) technique includes a fixed wavelength laser-light
source and a detector. The transmitted power of the near infrared light-
scattering signal is recorded during the depressurization process. Before
the onset, the signal transmitted is inversely proportional to the fluid den-
sity. During depressurization, the signal power increases. If particles
appear, then the signal power decreases (Gonzales et al., 2016).
Asphaltene inhibitors (AI) are used to reduce the AOP and thus miti-
gate the asphaltene-deposition tendency. In situ Asphaltene tests are run,
where state-of-the-art high-pressure/high temperature imaging technol-
ogy is routinely used in the laboratory to detect asphaltene particles very
clearly upon pressure depletion (Leontaritis et al., 2017).

6.2 ASPHALTENE FORMATION MECHANISMS REVIEW:
PRECIPITATION, AGGREGATION AND DEPOSITION
MECHANISM, SOLUBILITY

It is important to understand the differences between precipitation,
aggregation and deposition in order to properly explain the behavior of
asphaltene (Seifried, 2016). Experiments such as Electron Microscope,
Electrical Effect, Ultracentrifuge, and Reversibility have been conducted
to help determine existence states (Preckshot et al., 1943, Katz and Beu,
1945, Dykstra et al., 1944, Ray et al., 1957, Witherspoon and Munir,