SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, 2011
INTEGRATION OF IMAGE LOGS IN BROWN FIELD MANAGEMENT
Chandramani Shrivastva1, Khalifa Muslem
2, Sajith Girinathan
3, Benamer Djamila
3,
Koushik Sikdar4, Sarvagya Parashar
4
1 Schlumberger Oman & UAE; 2 Schlumberger Oman; 3 Schlumberger UAE; 4 Schlumberger India
ABSTRACT
Petrophysical applications of borehole images have long been established in the exploration and development of
hydrocarbon reservoirs, apart from the more obvious geological applications. The heterogeneity indices derived
from image logs in both clastic and carbonate reservoirs are used extensively for the infill wells to optimize
production with intelligent completions. Vuggy porosity, fracture porosity, and aperture computations have
contributed to static modeling of the reservoirs.
Image logs can be used effectively in Brownfield management as well, delivering meaningful input to improved oil
recovery (IOR) and enhanced oil recovery (EOR) processes. Water-injection programs need detailed insight of
geological complexities for better efficiency. The sedimentary structures and diagenetic imprints, which are nicely
captured on the borehole images, control the preferred flow directions of the waterflood and play an important role
in flood efficiency depending on the location of the injector well. Such features along with any fractures must be
taken into consideration when planning the location of injectors. Similarly, steamflooding for heavy oil production
also can capitalize on knowledge of fractures and sedimentary features. Polymer flooding for EOR, using the log-
inject-log methodology based on in situ evaluation also relies on using borehole images to understand flood
development and compare after-injection flooding with simulation results.
Brownfield management also requires regular updating of the reservoir model, with more data streaming into the
process. Successful well placement must take into account the stress regime in performing hydorfracturing, and here
borehole images play an important role. A successful stimulation job incorporates a lot of input from borehole
imaging logs, not only to understand the stress regime, but also to understand differential diagenesis, which
determines reservoir properties that control optimal recovery. Stimulation by acid or a frac pad must ensure that it
does not connect the well to any high-permeability streaks or fractures, which could significantly increase the water-
cut in production. This is a concern in Brownfield management, which also aims to arrest declining hydrocarbon
production over time.
Different methodologies for brown field development can be augmented with integrated applications of image logs
for optimizing the efficiency of non primary recovery processes. This paper introduces and summarizes how this
approach to successful brown field management honors geological complexity.
INTRODUCTION
Borehole imaging has been an integral part of logging programs for exploration well since long due to its application
in deciphering the geological complexities. The sub-seismic faults and fractures were always interpreted with
confidence on borehole images. The sedimentological applications of the image logs have been in place since the
dipmeter days as well. The famous red, green and blue patterns of interpreting the dipmeter data was applied in
understanding not only the structures, but also the depositional environments (Figure 1). With the advent of borehole
images (Figure 2), textural analysis was added to the geologist’s interpretation and gradually it led to the
development of petrophysical application of borehole images. Secondary porosity analysis, permeability estimation,
fracture analysis and Reservoir Rock typing are some of the largely used petrophysical applications based on the
high resolution image log data. Exploration geologists integrate the image logs with core and seismic to interpret the
sedimentary architecture (Shrivastva et al., 2008).
SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, 2011
Figure 1: Example of dipmeter interpretation with dip trends colored in red, green and blue
Figure 2: 2-D unwrapped presentations of Borehole micro resistivity image -captured features with the help of sine
waves
The development wells in many carbonate fields have taken advantage of the textural details and heterogeneity to
optimize the completions, with the help of swell packers and blinds; isolating the zones which could be potential
trouble makers in the near future (Shrivastva et al., 2009). The understanding of fracture distribution and their
physical attributes like density, porosity and aperture have long been extensively used in many studies.
However, the application of image logs is not limited only to the exploration and development wells. The brown
field exploitation still can derive plethora of information from the image logs to help in optimal recovery. An
attempt has been made here to understand the application of borehole images in the secondary (Improved Oil
Recovery, IOR) or tertiary (Enhanced Recovery Processes, EOR) recovery processes in various phases.
Dynamic Image Static Image
SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, 2011
IMAGE LOGS IN IOR/ EOR
The secondary and tertiary recovery processes aim at augmenting the reservoir pressure and altering the fluid
properties to facilitate flow of oil in to the well bore. Water flooding is an example of secondary recovery that
consists of planned injection well in pre-defined pattern to push the oil column up the producer well. The geological
understanding of sub-surface is very important to understand the existence of some natural preferred path of flow or
barrier to it. Image logs help a great deal in understanding the internal architecture of the sediments in clastic
reservoirs and existence of dissolution streaks in carbonate reservoirs. The presence of cross-beds in the sandstone
reservoirs (Figure 3) suggests the direction of least impedance to the fluid flow along it; whereas the fluid flow
across it would be difficult in comparison. A conceptual diagram in Figure 4 illustrates this. The injector in dark
blue shade would be more effective in its sweep to the producer well in red, compared to the injector in light blue
shade. The reason is: the water flood in dark blue injector would have to follow the easier path along the cross-bed
whereas the flood from the other injector would have to flow across the cross-beds as well.
Figure 3: Example of cross-bedded sands on core; with borehole images and dips (red tadpoles for cross-beds). The
image is a Static FMI normalized and oriented to North in a vertical well; and tadpoles are plotted from 0 to 90
magnitude.
Figure 4: Conceptual diagram with injectors (light blue & dark blue) and producer (red). The arrow shows
Paleocurrent direction.
Therefore, if the depositional architecture is properly understood, the injection program can benefit from this
concept. Jones et al. (1995) presented a study done by BP and Statoil Alliance that suggested that the sub-seismic
heterogeneities influence the water flood performance. In such experimental studies, the sedimentary structures and
their association with different units of depositional architecture tends to influence not only the flood patterns, but
also the flood efficiency. Feng et al. (2007) discussed the integration of geology in water injection optimization for a
complex heavy oil fluvial reservoir. Borehole images with their high resolution measurements capture the subtle
SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, 2011
changes and in texture and sedimentary structures; thereby helping in the conceptualizing the preferred flow
directions in the sub-surface when subjected to water injection. Similarly, the steam injection can be aided with the
sedimentological model built with the help of image logs. In fact, there are many examples where the image log
studies have helped in water/ steam flooding of the reservoirs.
Otiocha et al. (2001) discussed how integration of image logs helped in proper water flooding in Oman. Yose et al.
(2006) provide a very detailed account of water flooding problem and their solution with meaningful input from core
and geological studies in UAE carbonates (Figure 5). Such depositional models are built with image logs
contribution, in absence of core data and provide a major control on the design of injectors. The injector in the
diagram in Figure 5 cannot support the producer left to it, due to the flow barrier across the perforation. This is due
to the heterogeneity in the carbonates produced by the clinoforms. Similarly, dissolution seams and fracture corridor
end up consuming the injection water many times, thereby hampering the water flood movement towards the
production well.
Figure 5: Injector support available to only one producer, in carbonates reservoir with clinoform. Adapted from
Yose et al (2006).
The steam injection program is also planned to exploit any existing fracture network to maximize the EOR. The
example below in Figure 6 shows Static image in a highly deviated well, oriented with respect to Top of Hole. The
thermal treatment of heavy oil reservoirs can exploit the existing fracture system, which can be mapped with
borehole images.
Figure 6: Almost vertical fractures in the steam injector project could contribute to optimal treatment of heavy oil.
SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, 2011
IMAGE LOGS IN MICROPILOT
The MicroPilot concept is an offering for the EOR projects for quick screening of EOR process by altering
formation properties through the controlled injection of EOR-agents while measuring the recovery and/or
displacement behavior in-situ (Arora et al, 2010). The EOR fluid (with the polymers to be screened) is injected
downhole into the formation. The borehole images and saturation logs are recorded prior to and after the injection
and are compared for the changes in saturation. Borehole images are very important as they show the dimensions of
the swept zone (Figure 7). These measurements are run through reservoir simulation program to understand the
efficiency of the EOR polymers in the enhanced recovery of hydrocarbon on a field scale later on.
Figure 7: Schematic of Borehole image in MicroPilot, before and after injection
In the schematic (Figure 7), the left hand side reactance is a representation of borehole image, unwrapped in 2-D in
an oil bearing zone. The schematic is kept clean to illustrate the changes after the injection. The right hand side
reactance is the schematic of the borehole image after the injection. The red tiny point shows the injection point; the
blue shaded shape shows the conductive polymer flood and the yellow areola surrounding the polymer flood shows
the displaced oil rim.
IMAGE LOGS IN WELL-STIMULATION
Image logs play important role in the planning of well-stimulation by hydro-fracturing. The disturbance in the stress
regime manifests itself with drilling induced fractures or break-out on the borehole wall.
The borehole images with their high resolution measurements capture these signatures with their orientation. The
interpretation of this data provides information about the prevalent stresses direction (Figure 8). As a general
practice, the hydorfracturing is attempted to generate fractures in the direction of maximum horizontal stress
direction. At the same time, the frac length should honor the geological body orientation as well (Figure 9). A
fracture generated by stimulation might be planned wrongly running out of the sand body, thereby adding no value
for the extra frac pad it needed. The sand body geometry is interpreted with the help of the image logs in
conjunction with the core and seismic. A proper facies model can be developed and refined with the help of
borehole images (Shrivastva et al, 2008). The conceptual models thus developed in the sequence stratigraphic
framework provide clues about the possible reservoir distribution and their orientation.
SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, 2011
Figure 8: Solving for stress regime with the help of induced fractures and break-out captured on borehole images.
(Parashar et al, 2010)
Figure 9: Fracture length vs. sand body orientation
The image interpretation also helps by identifying the diagenetic patterns and the tightness they add to the formation
which can make the hydro-fracturing difficult. The fault zones or the fracture corridor which have been cemented by
preferential fluid flow and subsequent precipitation render hardness to the tight reservoirs. The open faults or
fractures if connected by hydro-fracturing to the aquifer can cause an early water-cut which needs to be avoided.
Therefore, while planning the well-stimulation job the image logs become very critical in not only understanding the
stress regime, but also for the successful post-stimulation performance honoring the structural and sedimentological
complexities of the formation.
CONCLUSION
Borehole images have long been used in exploration and development wells. However, their application in brown
field management is also very varied and equally important. There are many examples in the water injection and
steam injection projects where the high resolution measurements of borehole images have been put to use to identify
sedimentary features and facies association. The IOR/ EOR projects honor the geological complexity and
heterogeneity of the sub surface for optimal recovery which can be deciphered with the help of borehole images.
Also, the well stimulation projects need to understand the structural and sedimentological elements of the sub-
surface in addition to the local stress regimes. The existing borehole images from such fields can be used for further
integration in brown field management; and more data can be acquired to compensate for the existing data gap for
borehole images. The integration of image logs plays a very important role, with other existing data and model in
efficient brown field management.
SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, 2011
ACKNOWLEDGEMENT
Authors are grateful to the Schlumberger Middle East Asia management for their kind permission to present this
work. They also acknowledge different E&P companies across the Middle East Asia for the detailed discussions
about their brown field project practices.
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