In these recent times, energy resources especially related to fossil energy is being one of primary issues that we must deal with. As we know, the production of this resources have been declined in fulfilling every humans needs. The declining of resources production doesn’t meet the balance with the demands of global energy that has been growing faster through the times. In addition, the recovery factor of primary recovery in exploitation of oil and gas can only extract approximate 30 % of reserves related to natural physical properties initial pressure of fluid reaching to the surface. Therefore, in dealing this kind of problems, some oil company has the alternative to enhance the recovery with some advance methods, known as EOR. This recovery is related to wettability of rock as its physical properties of rock.
In the rock which contain oil and gas, there exists a surface tension between a fluid (oil and gas) with a solid. This surface tension has its angle when having contact with fluid (Ɵ). Every fluid has different contact angle when having contact with solid (rock) shown the figure 1 & 2 below.
Figure 1. Liquid/Solid/Gas wetting angle (Glover, 2012)
Figure 2. Contact angles and interfacial tension between common fluid (Glover, 2012)
From the picture above, it can be concluded that every fluid has differerent contact angle when having contact with solid (rock) and difference surface tension value. For example, 30o of contact angle when rock is saturated with oil – water.
The smaller angle of contact between common fluid saturates the rock (solid) means the fluid prefentially covers the surface, called as wetting fluid phase. In contrast, when the contact angle is larger than 90o causes the fluid cannot prefentially cover the surface of solid, known as non wetting phase. In wetting fluid phase condition, the fluid becomes immovable and trapped beneath surface tension between fluid and solid (rock). The wetting phase of fluid diminishes the value of recovery factor. To enhance the recovery factor, there are methods can be applied :
a) Primary recovery, this method applies the natural pressure of reservoir and sometimes add artificial tehniques in bringing oil to the surface. This method can only reach 30% recovery of reserves.
b) Secondary recovery, this method adds some artificial techniques, such as : injecting water, known as water flooding for displacing oil to the surface. This method successfully increases the recovery factor until 40 % of reserves.
c) Tertiary recovery (EOR), this recovery applies the advance tehniques, such as chemical treatment (surfactants, CO2 injection) and steam injections in high temperature to lower the viscosity of oil. This recovery sucessfully adds the production of hydrocarbon until 60 % reserves.
The tertiary method which is known as EOR have been applied for some oil field in Indonesia, such as : Minas Oil Field that is operated by Chevron Pacific Indonesia. For another case study in applying EOR is Berea Sandstone in Kentucky, USA (Adapted by : Fahes & Firoozabadi in SPE Journal 2004)
Berea sandstone has a decrease well deliverability because of appearance condensate reservoir that is related to the immobility of liquid phase of condesate reservoir and pressure drop after production, the reduction of condensate saturation enable to increase the gas well deliverability. To alter the condensate reservoir to intermediate gas wetting, there are some methods applied:
i. Injecting chemical treatment, 11-12 P ( 93% Ethy Alcohol, 5% Methyl Etyhl Ketone, 2% Fluoroalipathyc Silyl) at high temperature, 140oC
ii. Injecting chemical treatment FC 759 at high temperature, 140oC
iii. Injecting chemical treatment FC 722.
After doing some chemical treament at hight temperature, the core shows some alteration and increasing the viscousity and the mobility of liquid shown figure below :
Figure 3. The comparison of contact angle between the treated and untreated core (Fahes & Firoozabadi in SPE Journal 2004)
EOR is able to be applied for adding recovery factor of exploitation hydrocarbon within some advance tehniques to help lower the contact angle between solid and fluid, so the fluid will become movable and less viscous. This method is supported some artificial tehniques and some chemical treatments in adding the recovery factor of hydrocarbon exploitation.
- Glover, Paul. 2012. Formation Evaluation MSc Course Notes. University of Leeds. UK.
- Fahes & Firoozabadi .2007. Wettability Alteration to Intermediate Gas – Wetting Condensate Reservoirs at Hight Temperatures. SPE Journals, United Kingdom.
Aiman Haidar Shamlan