Summary
Water production becomes a major problem as hydrocarbon-producing fields
mature. Higher levels of water production result in increased levels of
corrosion and scale, increased load on fluid-handling facilities, increased
environmental concerns, and eventually well shut-in (with associated workover
costs). Consequently, producing zones are often abandoned in an attempt to
avoid water contact, even when the intervals still retain large volumes of
recoverable hydrocarbons. Many polymer systems have been applied over the years
to control undesired water production from hydrocarbon wells, with varying
degrees of success.
For approximately eight years, a polymer gel system based on an
acrylamide/t-butyl acrylate copolymer (PAtBA) crosslinked with
polyethyleneimine (PEI) has been used successfully for various water shutoff
applications. This article describes results from a sampling of over 200 jobs
performed throughout the world, including the average results from more than 90
jobs performed in one geographic location alone. In addition to “standard”
matrix treatments, results will be shown for other types of treatment,
including a design to plug annular communication and a combination of sealant
and temporary gel in an openhole horizontal completion. In addition, laboratory
data pertaining to work aimed at increasing the temperature limit of the system
will be presented. The upper placement temperature of the system originally was
~260°F. Data presented in this article indicates the development of a retarder
system that allows the upper placement temperature to be raised to at least
350°F.
Introduction
Controlling water production has been an objective of the oil industry
almost since its inception. Produced water has a major economic impact on the
profitability of a field. Producing 1 bbl of water requires as much or more
energy as producing the same volume of oil. Often, each barrel of produced
water represents some lesser, but significant, amount of unproduced oil. In
addition, water production causes other related problems such as sand
production, the need for separators, disposal and handling concerns, and the
corrosion of tubulars and surface equipment.
Many methods are available to mitigate water-production problems, and
perhaps the most widely used chemical system has been chrome-crosslinked
polyacrylamide gels. A previous publication described the advantages of the
acrylamide- (PAtBA) copolymer/polyethyleneimine system (herein referred to as
OCP, or organically crosslinked polymer) (Hardy et al. 1998). A brief
discussion of these advantages follows, with presentations of case histories
using OCP and data showing expansion of OCP technology.
OCP System Description
Gel systems for water and gas shutoff have many requirements, including:
- Low viscosity allowing easy injection deep into a formation matrix.
- Capability to control gelation time of the fluid.
- Sufficient strength to resist drawdown in the wellbore.
- Temperature stability of the gel for extended periods of time.
As will be shown in the following discussion, the OCP system meets all these
requirements. The viscosity of the system is ~25 cp as mixed. This relatively
low viscosity is due to the relatively low molecular weight, ~250,000, of the
PAtBA. This polymer is covalently crosslinked with PEI, which results in
excellent control over gelation time. Sufficient strength and temperature
stability are also obtainable. In addition, the OCP system is insensitive to
formation fluids, lithology, and/or heavy metals. Another advantage of the OCP
system is its predictable viscosity profile that can be used to improve
diversion over long treatment intervals.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
24 October 2005
- Revised manuscript received:
16 August 2006
- Manuscript approved:
19 August 2006
- Version of record:
20 May 2007
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