September 7, 2004

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Increased Production by Removal of Water Block at
Well Bores
Investigators Norman Morrow
and Jason Tong Chemical Petroleum
Engineering University of Wyoming
September 7, 2004
EOR Advisory Commission Meeting
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2003 Petrophysics Surface Chemistry Research
Group Left to Right Yongsheng Zhang, Herbert
Fischer, Ramil Ahmadov, Emin Babazade, Xina Xie,
Vusal Fataliyev, Carol Robinson, Hongguang Tie,
Zhengxin Tong, Li Yu, and Norman Morrow
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Current U.S. DOE Projects
Oil Recovery from Fractured and Heterogeneous
Carbonates  1.1M, Began July 2002. 3 yrs
Oil Recovery from Reservoirs Developed with
Environmentally Friendly Oil Base Muds 1.3M,
Began October 2001 4 yrs
Fundamentals of Reservoir Surface Energy as
Related to Oil Recovery from Fractured Reservoirs
by Spontaneous Imbibition 1.25M, Began July
2003, 5 years
EORI matching funds (used to support PhD graduate
students) support leveraged by a factor of over 15
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New Projects
Optimization of Injection Brine Composition BP
(Sunbury, UK) will visit UW on 8th - 10th Sept
Increased Production of Oil/Gas by Removing Water
Blocks
80K per year from new EOR support and matching
funds from Nautilus Resources for supply of rock
and oil samples and field tests
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Concept of water block

• Higher water saturation around the near-well-bore
  formation compared to the connate water
  saturation associated with rock that is more
  distant from the wellbore

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Origin of Water Block Project
Made presentation at the Society of Petroleum
Well Log Analysts Workshop on Reservoir
Wettability and Connate Water, Galveston, TX,
June 2003 Attended by Monty Hoffman, Nautilus
Resources (UW grad). Monty Hoffman and President
of Nautilus followed up with a visit to UW in
November of 2003 to discuss problem of
wettability and removal of water blocks.
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• Problem
• The clean-up or removal of water blocks is
  currently difficult and time-consuming.
  Chemicals are injected to alter the wettability
  at the well bore so that water is not retained by
  capillary forces. Treatment costs can be high
  and improvements may be temporary.

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New Approach
Fundamentals of a new approach to the water block
problem are based on results of a recently
completed project Wettability and Imbibition
Consequences at the Core and Field Scales U.S.
Dept. of Energy (1.9M), January 1999 through
February 2003
Best Technical Paper Award from the International
Society of Core Analysts
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Wettability Alteration Induced by Adsorption from
Crude Oils
Fundamental observation If crude oil is
displaced from a mineral surface by an alkane
(straight chain organic compound) the
wettability of the surface is changed to oil-wet
by a mechanism described as surface
precipitation. (Buckley, 1998)
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Imbibition
100
Oil Recovery
50
0
Time, t
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Berea Sandstones
Mineral oil
Crude oil
Crude oil displaced by mineral oil
Change toward oil-wet caused by displacement of
Minnelusa crude oil (Gibbs Field) with mineral oil
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Berea Sandstone
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Water-wet triangular pore
Additional oil/solid surface exposed by removal
of water
Wettability change over area of rock exposed to
crude oil
Additional area of rock surface exposed by
reduction in water saturation.
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Mixed-wet - Swi 31.2, 30.5, 27.6, 22.2, 20.3,
18, 16, 15, 14.1
VSWW(Swi 0)
Swi mixed-wet
Dimensionless time, tD
Sensitivity of imbibition to Swi for MXW
conditions
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Example of method of removing water block
(lowering the water saturation) and changing
wettability to oil wet
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(No Transcript)
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Can we design a treatment that is less costly and
more convenient ?
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• Wettability Alteration
• Alter wettability by displacement of formation
  crude oil by a suitable (preferably locally
  available) paraffinic (waxy) crude oil that
  causes change in wettability from water wet to
  oil wet by surface precipitation.
• Lab studies show that Dakota crude works well
• for all rock/oil combinations tested to date.

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• Reduction of Water Saturation
• Alternative approach to use of alcohol
• Surfactant - Use an oil-soluble surfactant at
  very low concentration to remove water as a
  dispersion (the opposite of using dishwashing
  soap to remove grease from dishes) and promote
  wettability alteration - extensive screening is
  in progress
• Use the formation crude or asphaltic crude to
  lower the water saturation by viscous flow. (Lab
  studies show cyclic treatment may work well)

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Field Tests
Targeted Oil Well Tensleep Black Mountain Unit
53 (About thirty miles east of
Thermopolis) owned by Nautilus Resources The
current plan is to use Dakota crude to induce oil
wetness by surface precipitation of asphaltenes
Contact Monty Hoffman, Nautilus Resources
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Field Tests
Gas Well Frontier formation (Crooks Gap,
Section 27, about 50 miles west of Rawlins) owned
60 by Nerd Gas and 40 by Wold Oil. Gas
production has fallen from 700 MCFD to 50-70
MCFD. The drop is ascribed mainly to water
blocking that followed a workover. Current plan
is to Displace water block by injection of
alcohol Inject a moderately asphaltic crude
oil Rely on gas production to induce surface
precipitation Retreat according to response
(economics) Contacts Dennis Brabec, Nerd Gas,
and Peter Wold, Wold Energy
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• Future Work
• Laboratory
• Continue testing for surfactant that reduces
  water saturation without adverse impact on
  wettability
• Determine what happens when treated surface is
  re-exposed to the formation crude oil Not a
  problem for gas wells.
• Check on wettability alteration (surface
  precipitation) by flow of methane.
• Identify optimum wetting conditions for
  eliminating water block
• Gas condensate blocks
• Field
• Field tests on the oil and gas wells will likely
  be performed by the middle of October.