Field Experience from a Biotechnology Approach to Water Flood Improvement

SPE 144205
Field Experience from a Biotechnology Approach to Water Flood
Improvement
B.G. Bauer, R.J. O’Dell, Merit Energy Company, S.A. Marinello, J. Babcock, T. Ishoey, Glori Oil Limited,
E. Sunde, Statoil S.A.
Copyright 2011, Society of Petroleum Engineers
This paper was prepared for presentation at the SPE Enhanced Oil Recovery Conference held in Kuala Lumpur, Malaysia, 19–21 July 2011.
This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been
reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its
officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to
reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.
Abstract
This paper is based on a field implementation in the United States of a biological process for improving waterflood
performance. The Activated Environment for Recovery Optimization (“AERO™”) System is being developed by Glori in
collaboration with Statoil and derives its roots from a microbial enhanced oil recovery technology developed and successfully
implemented by Statoil offshore Norway. Unique among IOR technologies, AERO implementation requires virtually no
capital investment and achieves high performance efficiencies at low operational cost. The simplicity of setup allows pilot
project implementation creating a very low risk entry point for the operator.
A pilot project was selected for a controlled investigation of the performance and impact. Robust testing was done in both
water and oil phases prior to treatment, confirming the potential for improved sweep and conformance from the project.
Subsequent implementation resulted in decreased water cut and increased oil recovery observable both at the wellhead and
allocated pilot levels.
This paper summarizes a rigorous analysis of the pilot project‟s performance to date, concluding that the production
improvement should be credited to the implementation of the AERO™ System.
Introduction
An AERO™ (Activated Environment for Recovery Optimization) System field pilot was initiated at the Stirrup Field in
southwest Kansas (Figure 1) to evaluate the potential improvement in recovery from a waterflooded reservoir. The field is at
a relatively mature stage of waterflood and following robust testing of the water and oil phases, it was believed that the
AERO™ System could enhance performance through improved sweep and conformance.
Figure 1: Location Overview for the Stirrup Field
Morton County, Kansas

2 SPE 144205
The Stirrup Upper Morrow „D‟ reservoir is a sandstone with a moderately to poorly sorted matrix deposited in a paleo
valley system encased in marine shales and located at a depth of 5,200 feet. The average net pay is 20 feet, with porosity
estimated at 15% and permeability at approximately 75 mD. The reservoir was discovered in 1985, with first production and
initial development coming from the gas cap. The oil column was not encountered until 1989. Further delineation
established that the Morrow „D‟ reservoir contains a very large gas cap relative to the size of the oil column1
. Conflicting
interests among the field‟s operators precluded attempts to implement allowables or put in place a reservoir management
plan. This resulted in primary production that focused on blowing down the gas cap, which ultimately impaired oil recovery.
When secondary recovery was finally implemented in 2003, reservoir pressure had declined from its initial value of 1,650 psi
to less than 100 psi across the field. This necessitated a more unique approach at waterflooding, whereby the majority of
injection wells were arranged in a curtain near the gas/oil contact, as shown in Figure 2. The produced oil gravity has been
between 38
and 41
API. Following gas cap production and limited primary oil production, the estimated recovery was only
13% of an estimated OOIP of 19.123 million barrels. Secondary recovery is forecast to yield an additional 2.75 million
barrels, for a EUR of approximately 27% of OOIP.
Figure 2: Stirrup Enhanced Recovery Unit w/ Water Curtain Wells Noted
The Stirrup AERO™ System pilot was initiated in May 2010. A broad-based bacterial inoculant and a specifically
tailored nutrient package were initially injected, with supplemental tailored nutrient injection to support development during
the course of the pilot. The project was applied to an irregular pattern, initially with two injectors and five producing wells
being sampled. It was anticipated that communication would develop along a dominant path between the injectors and a
primary producer, driven by existing flow paths and differential pressure conditions.
Field implementation resulted in improved recovery and water cut in the pilot area, but injected fluid volumetric
limitations and subsurface heterogeneity resulted in the pattern being restructured and the removal of an injector and a
producer from the active pattern. The justification for this change is summarized in a subsequent section. Although it did not
take place during the period focused on in this paper, another producing well was converted to an injector First Quarter 2011.
Before considering expansion into other areas of the field, an engineering evaluation was performed to ascertain any
contributing impacts from other potential factors that might affect observed incrementals and other aspects of the pilot‟s
performance.
Background
Biotechnology or Microbial EOR can be defined as the application of biological processes to facilitate, increase, or extend
oil production from a reservoir. As with all EOR processes, the goal is to improve recovery performance by mobilizing oil
left behind by primary production mechanisms, or secondary water flooding operations. This is an old concept, with pilot
Morrow ‘D’ Sandstone (20’ net, 15% Φ, 75 md, 32% Swc)
13 Producers / 15 Injectors (11 forming “water curtain”)
Areal Extent ≈ 5,300 acres, Depth ≈ 5,200’ MD
OOIP ≈ 19 mmbo [23% RF], OGIP ≈ 45 bscf [95% RF]
Current Prod / Inj ≈ 490 bopd, 7,041 bwpd, 13,801 bwipd
Santa Fe Trail A
WATER CURTAIN WELLS
(separating oil leg from gas cap)
Discovery well

SPE 144205 3
tests dating back to the 1950‟s and considerable activity and research directed to the topic during the late 1970‟s and early
1980‟s. The body of research and pilots performed resulted in a fair amount of literature, but skepticism about the
mechanisms of the processes and implementation of the technology led to limited consideration or adoption within the
industry. Part of this has been due to the fact that it is a complex process spanning multiple disciplines, as well as disparity in
field performance compared to laboratory results; a fairly common issue with EOR technologies. Some mixed results in
practice would appear to be poor field implementation and/or project design, which may be attributable to an incomplete
understanding of how microbial activity might affect oil recovery mechanisms. Advances in microbiology in the last decade
have led to a revised interpretation of these historical approaches and facilitated the birth of a new generation of
biotechnology applied to improve oil recovery2
.
The AERO™ System has been developed to improve waterflood performance and increase recovery via a combination of
mechanisms dominated by two specific processes:
 Improved sweep efficiency due to micro diversion of fluid pathways at the pore level
 Interfacial tension reduction & residual oil mobilization via surfactant-like behavior of microorganisms.
As was noted earlier, it was anticipated that microbial processes would develop along a dominant path between the
injectors and a primary producer, driven by existing flow paths and differential pressure conditions. Sweep alteration and
residual oil mobilization were the expected mechanisms for the Stirrup pilot.
Baseline Waterflood Performance Evaluation
In order to evaluate the performance of the AERO™ System pilot, it was necessary to ascertain the actual performance
and mechanics of the ongoing waterflood across the Stirrup Field prior to project initiation. The implementation of „water
curtain‟ injection wells focused on the gas/oil contact in order to isolate the depleted gas cap from the oil zone. This resulted
in the (anticipated) loss of the majority of injected water from these wells into the gas cap. In order to be able to assess the
real impact of the AERO™ System on oil and water production from the wells included in the pilot, an accurate estimate of
the actual injection and withdrawal associated with the pattern‟s pore volume under the existing waterflood operation had to
be determined. In performing a field level evaluation, a better understanding of the displacement dynamics in and adjacent to
the pilot was obtained.
Industry accepted techniques for waterflood evaluation were used to establish well allocation factors on injectors and
producers for the purposes of pattern analysis3
. These factors were optimized by using the resultant allocated production &
injection volumes in fill-up calculations, which were tied back to actual waterflood response as shown in rate-time, Jordan,
and Staggs plots. Figures 3 and 4 show the disparity between the total injected volume and the apparent water volume
Figure 3: Disparity between Calculated and Actual Fill-up
0
5,000
10,000
15,000
0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000
Production,mb
Injection, mb
Total Liquids Withdrawal
Cumulative Oil Production
Estimated Fillup
Jordan Plot
Stirrup ERU

4 SPE 144205
Figure 4: Reduction in Applied WAF’s Provide Consistency with Withdrawal Data
entering the field. Adjustments to the well allocation factors were made to match the performance history for water
withdrawal and oil production prior to the onset of the AERO™ System pilot.
Well Performance Evaluation
The economics of a mature waterflood on a field the size of Stirrup make the implementation of EOR techniques difficult
due to the capital investment required by most methodologies. The objective of the pilot was to show that the AERO™
System could be implemented with minimal capital investment and successfully increase oil production and anticipated
ultimate recovery. A re-evaluation of waterflood performance was performed after the early results of the AERO™ System
pilot had been reviewed. It was apparent that the volume of injected water entering the pilot pattern was less than that
required to provide sweep. This affected the ongoing pilot and field operations as water was reduced to certain injectors. As
a consequence, some producing wells were subsequently designated for conversion to injectors.
The pattern utilized in the SERU (Stirrup Enhanced Recovery Unit) AERO™ System pilot was designated 4-1, as it is
centered on the SERU 4-1 injection well (Figure 5). Two injectors were initially inoculated on May 20, 2010; SERU 4-1 and
SERU 5-3. Pilot production was monitored at SERU wells 2-1, 4-2, 5-1, 10-1, 10-2, and 12-2. After several months of
operation, it became apparent that SERU 5-3 was not actually operating as part of the test pattern; the water injected there
was not entering the pilot area. This determination was based on an analysis of injection and withdrawal in the eastern
portion of the field. In short, the total withdrawal from nearby producers did not nearly equate to the volume of water
injected into the 5-3 and the inclusion of this well in fillup calculations prevented any semblance of a history match to actual
data as shown in waterflood analysis plots. Further evaluation of three-dimensional seismic data shows that this well bisects
the easternmost fault. It is likely that injection into this well is being lost through this fault. Therefore, SERU 5-3 was
removed from the pilot analysis. It became apparent, with this realization, that the pilot area was not receiving sufficient
water injcetoin from SERU 4-1 to achieve the sweep potential envisioned in the original design.
0
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14,000
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18,000
20,000
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000
Production,mb
Injection, mb
Total Liquids Withdrawal
Cumulative Oil Production
Estimated Fillup
Jordan Plot
Stirrup ERU

SPE 144205 5
Figure 5: Injection Pattern 4-1 Pilot Configuration with Updated Well Status
SERU 12-2, located northeast of the 4-1 injection well, was the only producer to show a markedly positive production
response. It exhibited a significant increase in oil production three and a half weeks following initiation of the pilot.
Production increased as much as 200%, and then fell to a rate corresponding to a 60% increase going forward. The
stabilized rate is greater than the 2009 average. Water production was elevated for the first period and followed the same
pattern. However, water production did not increase by the same factor as the oil, more closely paralleling the change in total
produced volume. As such, the approximate water cut decreased. The 12-2 well had seen an increase in both oil and water
production following a pump change two months prior to project initiation. Water cut had decreased following the exchange
of the pump, decreasing to approximately 88%, but had begun to increase just prior to pilot initiation. It was approximately
91% at the onset. Water cut then fell significantly to a level as low as 85% during the period of greatest production increase.
By May 2011, water cut had returned to 91%.
Based on proximity to the 4-1 injection well, incremental oil was first anticipated to show up at SERU 5-1. However,
production from 5-1 actually decreased slightly after initiation, although there was a short period of increased production in
June 2010. Production fell slightly more after that time and then remained relatively stable until mid-January 2011. At that
point, production again increased for a couple of weeks, but fell thereafter. These variations are, again, likely due to transient
diversions in water support. As they do not seem to be related to injection in 4-1, it raises the question as to how much
support is coming from the pilot injector. The well does not appear to be damaged, which may indicate that the permeability
in the area towards the edge of the structure is tighter than elsewhere.
It had been expected that the most significant impact of the pilot would be felt in the path generated between the injector
and the producer with the lowest potential; that is, with either the lowest bottomhole pressure and/or the flow path of least
resistance. Preferential flow direction is based on the differential pressure between two points and the mobility between
them, which is function of permeability, or relative permeability, and effective viscosity, which combines to provide
resistance or ease of flow along a particular path. Fluid will always follow the path of least resistance. The answer to why
the greatest impact was felt at SERU 12-2 may be attributed to the path of least resistance having been established during
waterflood operations. The communication paths from 4-1 to the 12-2 and 5-1 wells are roughly orthogonal to each other. A
review of the regional stress data shows that the direction of maximum stress runs SW-NE. This parallels the path between
SERU 4-1 and SERU 12-2. During waterflood operations, it is possible, or likely, that some limited fracture was initiated
between the two wells. That initial path would be sufficient to have flow preferentially move towards 12-2. Once
established, diversion of flow and/or release and activation of residual oil would take place more readily along the interfaces
along the path.
Mindful of these issues, producer SERU 2-1, which had not exhibited significant impact during the pilot, was taken off
line during mid-March of 2011, and converted to an injector. Although its position relative to SERU 5-1 is not exactly
10 11
23
GOC- 20
25
-2000
5212-
0012-
- 2
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-2200
0502-
- 2050
5202
-
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W
SERU 12-2
89 bopd
941 bwpd
SERU 10-2
43 bopd
817 bwpd
SERU 4-1
911 bwipd
1,189 psig
SERU 2-1
410 bwipd
1,281 psig
SERU 5-1
25 bopd
412 bwpd
SERU 5-3
0 bwipd
1,208 psig
SERU 4-2
29 bopd
278 bwpd
STIRRUP FIELD
MEOR Project Area
Pilot Pattern
FEET
0 500 1,000
POSTED WELL DATA
Well Name
WELL - AVG_BWIPD[PROCOUNT] (bwipd)
WELL - AVG_TP[PROCOUNT] (psig)
WELL - AVG_BOPD[PROCOUNT] (bopd)
WELL - AVG_BWPD[PROCOUNT] (bwpd)
CONTOURS
OOIP
OOIP.GRD
Contour Interval = 0.5
Created : 24 Aug 2009, 3:33 PM
Grid Size : X=164.07 Y=165.06
127 Rows by 200 Columns
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
WELL SYMBOLS
Oil Well
Injection Well
Service Well
Plugged and Abandoned
W
Converted Water-Input Well
Shut-In Well
May 12, 2011
PETRA 5/12/2011 6:25:22 PM

6 SPE 144205
parallel to the stress direction, the situation is notably better than SERU 5-3 and as it adds critical volume to the pilot
injection area, there may be an increased likelihood that a flow path will be established between the two wells.
SERU 2-1 production had not changed in the first five months of the pilot. Oil production increased suddenly and
erratically in September 2010, with water production increasing as well, while the water cut, which had been trending
upward, fell back slightly to 96%. Oil production returned to earlier levels within weeks, but water production increased and
the water cut went back up; from roughly 96% to almost 98%.
Oil production decreased at SERU 4-2 shortly after initiation, which would suggest that there was some diversion of
water support from its drainage area at that time, with transient variations causing the minor production increases in February
and April of 2011, while water production remained stable.
SERU 10-1 saw a reduction of water production in late 2010 and into 2011, with an oil production increase in February.
These results did not correlate with the 4-1 pattern and it was later determined that 10-1 was on the western side of an
apparently sealing fault, isolated from the pilot pattern. SERU 10-2 had seen a short term increase in oil production shortly
after the pilot was started, with relatively stable water production. The responses seem to indicate some communication with
injectors other than, or in addition to, 4-1.
The fluid production variations for the non-responding wells have not been of magnitudes significantly different from
typical operating ranges. There have been a number of divergent impacts on the various producing wells, but they do not
necessarily show any interdependent relationships. It would be hard to characterize such interdependencies given the
distances and time delays. The lack of dependent responses indicates that the inoculant and nutrients did not get established
along communication paths with the 4-1 injector.
AERO™ System Pilot Performance Evaluation
Because the gathering and allocation for the pilot area is tied up in the field system and Stirrup lacks a highly accurate
dedicated testing system or individual separation, an evaluation can only be made on relative performance on a well by well
basis. Un-controllable well events and injectivity changes in other areas of the field appear to have masked many of the
positive effects of the pilot program. However, the favorable results seen within the pilot are quite encouraging.
As noted, the overwhelming majority of the total pilot response was at SERU 12-2. It is felt that, through this period,
insufficient water was entering the 4-1 pattern to impact any other wells. Subsequent follow-up work suggests that the other
production wells within the pattern have been predominantly influenced by adjacent injectors due to these volumetric
limitations. Therefore, the performance improvement observed, with consideration of various operational upsets, was almost
entirely due to the result of the oil mobilized between SERU 4-1 and SERU 12-2. Figure 6 presents the production history
for the 4-1 injection pattern through the end of 2010. The uptick in production corresponding to the response of the SERU
12-2 is clear.
Figure 6: Injection Pattern 4-1 Production History
Figure 7 presents a plot of oil cut vs. cumulative recovery, providing for comparative predictions of waterflood and
BEOR recovery. For the extended period of the pilot, while production did increase at 12-2, it did not fall off significantly in
the rest of the modified pattern. The production and recovery data are shown again in a classic rate-time plot in Figure 8, in
1
10
100
1,000
10,000
1980 1985 1990 1995 2000 2005 2010
AverageMonthlyRates
bopd
mcfpd
bwpd
bWINJpd
Expected Response
Production History
Pattern 4-1 (INJ Centered)

SPE 144205 7
which the estimated recovery from primary, secondary, and BEOR implementations are shown to be 20.2%, 42.7% and
45.9% respectively for the injection pattern. That estimate is for the complete injection pattern volume, but it is believed that
only a fraction of that volume, specifically the volume related to SERU 12-2, is being swept, due to the prevalent well
relationships established during waterflooding, as well as because of insufficient water being injected into the pattern.
Assuming that the pattern volume associated with 12-2 is approximately 25% to 35% of the total, the incremental recovery
from the impacted volume is estimated to be between 9% and 12%. However, the true swept area between these two wells is
unknown, and further work is required to resolve the improvement to sweep efficiency and corresponding incremental
benefit. Further work & extension of the pilot is planned. This modification and expansion has and will focus on providing
sufficient injection volumes and on improving the sweep in the targeted areas.
Figure 7: Pattern 4-1 Oil Cut vs. Cumulative Oil Recovery Factor
Figure 8: Pattern 4-1 Production Forecasts –EUR for Primary, Secondary and BEOR
Focusing on the SERU 12-2 well alone and analyzing well test data, Figure 9 compares oil cut to oil production over the
life of the well. Trend extensions for waterflood and AERO™ recovery at the oil cut limit suggest 40 mbo of incremental oil
over the life of the well. Note that the short term deviation prior to the end of the year was from a field allocation effect;
Jan-06
Jul-06
Jan-07
Jul-07
Jan-08
Jul-08
Jan-09
Jul-09
Jan-10
May-10
Jul-10
Sep-10
Nov-10Dec-10Jan-11Feb-11Mar-11Apr-11
y = 565.51e-0.012x
R² = 0.9471
1%
10%
100%
400 450 500 550 600 650 700 750 800 850 900 950
OilCut
Np, mbo
Oil Cut, Fo
Culled Data Set
Expon. (Culled Data Set)
Oil Cut vs. Cumulative Oil Production
EUR ≈ 5,259 mbo
Remaining ≈ 843 mbo
1
10
100
1,000
1995 2000 2005 2010 2015
bopd
Actuals
Primary Forecast - Conventional DCA
Secondary Forecast (Fo-RF Correlation)
Incremental MEOR Forecast
Rate - Time Plot

8 SPE 144205
production during that period was essentially unchanged. Figure 10 plots water cut vs. oil production and shows that there
was a significant reduction in water cut during the initial peak incremental production period of the pilot. Water cut at the end
of the year had nearly returned to pre-pilot levels, which would tend to suggest banking of the oil along the path between
wells.
Figure 9: SERU 12-2 Oil Cut vs. Np – Waterflood and BEOR Projections
Figure 10: SERU 12-2 WOR vs. Np
Oil and water production are both plotted against time in Figure 11, clearly indicating the incremental production when
the mobilized oil arrived at the well. Projections indicate estimated decline trends for both waterflooded and AERO™ cases.
As shown in Figure 12, which plots oil production rate vs. cumulative production, it is estimated that 17,604 bbls of
5/16/2006
6/26/2006
11/14/2006
12/26/2006
2/10/2007
4/18/2007
7/13/2007
8/14/2007
9/19/2007
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(3/05/07)DHFailure
(10/03/07)DHFailure
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EquipProblems
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(9/10-9/14)PlantProblems
(10/20/10)DHFailure
1.00%
10.00%
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150 200 250 300 350 400 450
Np,mbo
OilCut, Fo
Comments Series
Pre-MEORForecast
Post-MEOR Forecast
SERU12-2 --- WellTestAnalysis
Jan-08
Jun-08
Jan-09
Jun-09
Jan-10
Jun-10Jun-10Jun-10Jun-10Jun-10Jun-10
Jun-10
Jan-11Jan-11Jan-11Jan-11Jan-11Jan-11Jan-11Jan-11Jan-11Jan-11Jan-11
1
10
200,000 220,000 240,000 260,000 280,000 300,000 320,000 340,000 360,000 380,000 400,000
Water-OilRatio
Np, bo
WOR
Labels
SERU 12-2
Well Tests Analysis
WOR - Cumulative Oil Production Plot

SPE 144205 9
incremental production were recovered from SERU 12-2 by years end. Oil production has fallen by over half since the peak
monthly rate in June 2010, but it is still approximately double the expected rate prior to the onset of the pilot and pump
upgrades.
Figure 11: SERU 12-2 Oil and Water Production Rate Histories and Forecasts
Figure 12: SERU 12-2 Oil Production History and Forecasts
-----
200
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2008 2009 2010 2011
bwpd
bopd
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12/26/2006
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4/18/2007
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10/18/2010
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1/2/2011
(3/05/07)DHFailure
(10/03/07)DHFailure
(3/01/08)DHFailure
(3/17/10)DHFailure
EquipProblems
(6/10/10)DHFailure
(9/10-9/14)PlantProblems
(10/20/10)DHFailure
-----
20
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200 220 240 260 280 300 320 340 360 380 400
Np,mbo
bopd
Comments Series
Post-MEOR ProjectForecast
Pre-MEORProject Forecast
Constant processing rate (1,050 bpd)

10 SPE 144205
Summary
The Stirrup AERO™ System Pilot was implemented to determine if incremental oil could be recovered from a reservoir
at a mature waterflood stage. The pilot was based on certain premises and expectations, some of which occurred, and some
that didn‟t. Anticipated production from SERU 5-1 did not materialize, but further evaluation of waterflood pattern response
and stress orientation in the field suggested that there would have been preferential flow between the SERU 4-1 injector and
the SERU 12-2 producer, which is what has occurred during the course of the pilot to this point. In evaluating the allocated
contribution of water injection to the 4-1 injection pattern and considering the pilot performance, which was dominated by
the 12-2 well, it was estimated that 3.2% additional incremental oil would be recovered from the pattern pore volume by the
end of operations, if they continued as originally implemented. Analysis showed, however, that the pattern was not receiving
sufficient water to allow coverage and that the incremental oil was recovered from only 25% to 35% of that pore volume,
which translates into a 9% to 12% incremental recovery from the pilot application if the given volumetric assumptions are
correct.
Steps were implemented in early 2011 to improve water supplied to the pattern, with the conversion of the SERU 2-1
producer to an injection well. Expansion of the pilot to the larger part of the field is also being planned, and consideration of
the possible impact of stress orientation and existing communication paths will impact the design and expectations of that
effort.
References
1. Thurmond, T. and Sembritzky, Chris.:”Reservoir Stimulation Study, STIRRUP FIELD, Morton County Kansas”,
Anadarko Petroleum Corporation, Dec. 2001
2. Torsvik, T., Gilje, E., and Sunde, S. (1995). Aerobic Microbial Enhanced Oil Recovery. Proc. 5th Int. Conf.
Microbial Enhanced Oil recovery, Dallas, Texas, US. pp 439-452, 1995.
3. Cobb, W.M., and Smith, J.T.: “Waterflood Surveillance,” WATERFLOODING: PERFORMANCE PREDICTIONS
AND SURVEILLANCE, Industry Course, William M. Cobb & Associates, Dallas, TX (2007), Chapter 9.

Field Experience from a Biotechnology Approach to Water Flood Improvement

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