IOR 2009 - 15th European Symposium on Improved Oil Recovery

BP s current and future hydrocarbon portfolio contains a significant proportion of oil resources which are
the target of new EOR techniques being developed by BP to improve recovery beyond what is possible
with conventional methods. These techniques are focussing on improving both pore scale displacement as
well as sweep efficiency.

Many studies on Microbial Improved Oil Recovery have demonstrated that bacteria have a positive effect
in regard to reduce the residual oil saturation. Possible mechanisms of IOR as a result of bacterial activity
are; interfacial tension reduction, change of wettability, gas production and conformance control through
selective blocking of the most permeable pore channels. Understanding which mechanisms allow bacteria
to increase oil recovery and how these mechanisms occur and interact is the key to better understand and
to get a clear insight into the complex MIOR processes.

Rising importance of using Enhanced Oil Recovery (EOR) in oil production also increased the demand for
monitoring related effects like surface movements. Over the last years land surface movement monitoring
using satellite Synthetic Aperture Radar (SAR) interferometry became operational. In the last year a new
generation of SAR satellites with high resolution modes and short revisit times was launched and
interferometric data series are available. This development reveals the potential for monitoring small-scale
and highly dynamic surface movements related to EOR more accurate than by using conventional systems.

Carboxylic material present in the crude oil, quantified as acid number (AN), is believed to be the most
important wetting parameter for carbonates. The water wetness decreases as the AN increases. At high
temperature, seawater is able to displace some of the adsorbed carboxylic materials, and seawater
therefore acts as a wettability modifier causing increased oil recovery both by spontaneous imbibition and
by forced displacement. It has been documented that interactions between ions present in seawater, Ca2+,
Mg2+ and SO42-, and the chalk surface are responsible for the wettability modification. The properties of
the carboxylic material may have influence on the initial wetting conditions and also on the wettability
alteration process. In this paper we have extracted water soluble acids from a crude oil with high AN. The
original oil (AN=1.8 mgKOH/g) and the treated oil depleted in water soluble acids (AN=1.5 mgKOH/g)
were used to study wetting properties and oil recovery by spontaneous imbibition with chalk as the porous
medium. The water wetness appeared to be lower for the original oil compared to the treated oil. In a
spontaneous imbibition process with wettability modification at 110 °C, seawater imbibed faster into the
cores saturated with the treated oil containing no water soluble acids.

Steam injection is becoming increasingly used to enhance heavy oil production even in complex reservoirs
such as fractured carbonates. However, injecting steam into fractures has the potential to change reservoir
permeability because increasing the temperature causes the reservoir rock to expand potentially closing
fractures and condensed water may react with the reservoir rock; both processes may increase uncertainty
in predicting oil recovery from these reservoirs.

It is well known that time-lapse seismic can improve the Oil or Gas recovery from existing reservoirs and
it has been taken as a powerful tool for reservoir management. It shows how a reservoir behavior changes
at different development times and provide valuable information for further development plan. In this
paper, a prediction method with ANN (artificial neural network) based on time-lapse seismic prestack
elastic parameter inversion is introduced to describe the oil or gas saturation variation and reservoir
pressure change.

The effect of the aqueous chemistry on the mechanical strength of chalk has been studied extensively at
the University of Stavanger. At high temperatures (~130°C) chalk exposed to seawater is significantly
weaker compared to chalk exposed to distilled water as considering the hydrostatic yield strength and the
following creep phase

Fate of microorganisms in porous media has very important applications in many branches of
environmental and petroleum science and engineering, like in the Microbial Enhanced Oil Recovery
(MEOR) processes, among others; however, concurrently it is a very complex and interacting phenomenon
mainly because microorganisms are living. Applying the systematic modeling approach to continuum
systems, we derive a model that include net flux of microorganisms and nutrients by convection and
dispersion, growth and decay rates of microorganisms, chemotactic movement and nutrient consumption,
adsorption of microorganisms and nutrients on rock grain surfaces, as well as desorption of
microorganisms. Porosity reduction due to cell and nutrient adsorption is considered. We implement the
model within a Finite Element Method. The numerical simulations reproduce results previously reported
elsewhere; moreover, we show the spatial-temporal distribution of microorganisms and nutrients along the
system and time. We point out the complementary role of the spatial-temporal distribution of components
with breakthrough curves to analyze the behavior of both fluent and adsorbed components.

Foam can increase sweep efficiency in gas-injection IOR processes. Here we develop design criteria for
surfactant-alternating-gas foam processes in layered reservoirs. We reach the following conclusions:
Trends of foam strength with permeability or surfactant formulation, as measured in conventional
coreflood tests at fixed injected water fraction, may not correspond to behavior in a SAG process in the
field. In the cases examined, foam strength in a SAG process is much less sensitive to permeability and
foam parameters than is foam strength at fixed injected water fraction.
Placement of surfactant into low-permeability layers is a key challenge of SAG processes in
heterogeneous reservoirs. Gas breakthrough occurs via low-permeability layers that did not receive enough
surfactant. For that reason, a stronger foam that more effectively diverts flow away from higherpermeability
layers may send more gas to lower-permeability layers that lack surfactant, and thereby
accelerate gas breakthrough.
Using multiple surfactant and gas slugs allows foam to redistribute surfactant in later slugs.
However, this strategy suffers from poor injectivity during liquid injection, which slows the process and
promotes gravity segregation.
Injection of both gas and surfactant slugs at the maximum allowed injection pressure, rather than
at fixed rate, gives best results.
Injecting gas from only the bottom of the well offers no significant advantages in the best case,
where a high-permeability layers lie at top and bottom of the reservoir, and performs significantly worse if
low-permeability layers lie at the top (where lack of surfactant leads to override) and bottom (where low
permeability restricts injectivity) of the reservoir.
A surfactant slug sized for a homogeneous reservoir is too large for a heterogeneous reservoir,
because little surfactant enters lower-permeability layers: much of the injected surfactant goes to waste. A
surfactant slug sized to sweep high-permeability layers and a portion of low-permeability layers performs
nearly as well as one sized to sweep the entire reservoir.