Page 280 - Formation Damage during Improved Oil Recovery Fundamentals and Applications
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Formation Damage by Organic Deposition                       251


              electron microscope (SEM) with energy dispersive X-ray spectroscopy
              (SEM-EDS) and X-ray computed microtomography to study the crude oil
              volumes at the pore scale in order to quantify residual oil and wettability
              alteration (Seifried, 2016).





                   6.3 ISSUES WITH ASPHALTENE DEPOSITION

                   6.3.1 Asphaltene issues during oil production
              Precipitation, aggregation, and deposition of asphaltenes are a huge prob-
              lem in the field, especially with the injection of CO 2 as a means of
              enhanced oil recovery, since they lead to precipitation when crude oil is
              mixed with CO 2 .
                 Crude oil exists in hydrocarbon reservoirs which are system consisting
              of reservoir rock and reservoir fluids. Porosity and permeability are the
              most important pore structure characteristics used in the discussion
              of hydrocarbon-reservoir-rock systems. For reservoir fluids, the composi-
              tions may vary from region to region, and typically overlay an aquifer,
              and are capped by a gas zone (gas cap). Due to multiphase flow behavior
              under varying pressure and temperature conditions, hydrocarbon systems
              are typically complex (Ahmed, 2006)


              6.3.2 Formation damage and field experience
              The precipitation of asphaltenes during all phases of crude oil recovery
              can lead to a decrease in production efficiency. Leontaritis et al. (1994)
              stated that generally four forms of formation damage induced by asphal-
              tene deposition can be defined: (1) The physical blockage or permeability
              reduction, (2) wettability alteration, (3) a crude oil viscosity decrease, or
              (4) the formation of a water-in oil emulsion. Mechanism (1), however,
              seems to be the dominant one causing formation damage. The first step
              of asphaltene deposition is the adsorption of the asphaltene molecules on
              the surface of the rock, followed by hydrodynamic retention and/or trap-
              ping of the particles at the pore throat, eventually leading to a reduction
              of the effective hydrocarbon mobility (Nghiem et al., 1998; Al-Maamari
              and Buckley, 2003). Zekri et al. (2007) investigated how different flow
              rates in dynamic flow experiments affected formation damage due to
              asphaltene deposition. They stated that a decrease in the flow rate may
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