Page 188 - Primer on Enhanced Oil Recovery

178 Primer on Enhanced Oil Recovery

methods before. Renewable energy allows to reduce carbon footprint of all opera-
tions and has the potential to be practical economical choice. The renewable energy
utilization is slowly incorporated in all oil extraction processes. The overall renew-
able energy price is constantly reduced and the price now became comparable with
gas energy generation.
Currently, most energy for oil extraction is produced by electricity or by utiliza-
tion of hydrocarbons. Solar light brings energy to many places at the amounts
2 2
between 1 and 1.5 kW/m , this converts into an average of around 2000 kWh/m /
year. It is feasible at the moment to generate electrical power from it with an eco-
nomically viable efficiency between 10% and 20%. Electrical energy is very flexi-
ble in a sense that it can power many processes and machinery.
Much higher efficiency at solar light utilization is achieved by solar thermal technol-
ogy. Nowadays some companies claim that around 90% of solar energy can be con-
verted into the heat energy. This energy then can be used to heat a formation, for
instance. In order to be an economically viable the site installation should be big enough
and this requires significant financial outlay and considerable time to get the return.
Few projects in this area have been undertaken. Generally, the results are vari-
able. Some installations have been successful while others were not so. As usual,
the susses follows detailed planning, careful installation and site management.
Many governments in oil producing countries have developed renewable energy
deployment and use programs.
It is absolutely clear that the renewable energy use will be widened and success-
fully used in Enhanced Oil Extraction processes.
14.7 Heavy oil fields

The advantage of heavy oil is in its abundance. The disadvantage is in high viscosity
and difficulties to recover it. Steam Assisted Gravity drainage (SAGD) has been
developed and successfully used. In situ combustion is also very effective method, as
was discussed before. Unfortunately, both of those methods are not good for thin for-
mations. The oil community slowly realises that it is possible to use high viscosity
displacement media such as surfactant-polymer flooding and high temperature dis-
persed systems for heavy oil recovery. An example can be a foamed steam which has
much higher viscosity and allows much better sweep efficiency due to more
stable oil displacement. Some surfactants are stable at temperatures above 200 C.

Added to a water with some noncondensable gas (the gas, nitrogen for example, par-
tially stabilises bubbles) such surfactants allow to generate steam-foam and eliminate
simple steam displacement front instability. It is possible to use other dispersed sys-
tems which properties can be further propped by addition of various catalysts.

14.8 Combined methods

Each EOR method by itself has its limitations. We have described before how com-
bination of methods, like injection of various slugs, help to achieve fuller oil