Summary
The use of water-in-oil emulsions (W/O) to deploy scale inhibitors has been
reported in the literature as an alternative to water-based squeeze treatments.
The non-aqueous nature of these emulsions has the advantage of preventing water
blocking, which adversely affects oil production in aqueous squeeze treatments.
Placing the scale inhibitor in a w/o or “invert” emulsion has shown in some
cases the additional advantage of enhancing treatment lifetime. However,
results from the literature seem contradictory sometimes and highlight a poor
understanding of this technology.
The present paper aims at providing further insight on emulsified scale
inhibitor placement in porous media. We focus on studying the retention
mechanisms of the emulsion droplets containing the scale inhibitor (SI),
whilst SI release and, consequently, the performance of the emulsified squeeze
is not discussed here. Preliminary experiments were conducted using a low
molecular-weight biopolymer as a scale inhibitor. They evidenced a low
adsorption/retention of this SI in aqueous solution. Reformulation of the
product under invert emulsion was investigated to enhance inhibitor
retention.
Results from coreflood experiments using well-characterized silicon carbide
(SiC) packs provided preliminary evidence of aqueous droplet adsorption as the
main retention mechanism in porous media. This was expected considering the
average droplet size of 0.3 mm (300 nm). The mother formulation of the
w/o emulsion is a concentrate, containing 80% weight of water phase and 8%
weight of active scale inhibitor. The product can be diluted down to 2% water
phase by adding the desired oil phase. Dilution does not affect emulsion
stability or increase the emulsion's droplet size. These results
represent a promising first step towards the development of a technically and
commercially viable, environment-friendly scale inhibitor technology based on
w/o emulsions. Future work to study the emulsied SI release
mechanisms and its consequent performance are being prepared to compare with
conventional aqueous squeeze treatments.
Introduction
The formation of mineral scale in production facilities is a relatively
common problem in the oil industry. Most scale forms either by pressure and
temperature changes that favor salt precipitation from formation waters, or
when two incompatible waters mix during pressure maintainance or waterflood
strategies. Scale prevention is achieved by performing “squeeze” treatments in
which chemical scale inhibitors are injected into the producer near
wellbore.
Once the scale inhibitor is injected, it is retained in the porous matrix
and hopefully it will be returned with produced fluids in slow enough rates to
assure long treatment durability and lifetime. Many conventional squeeze
treatments, where scale inhibitors are injected in aqueous solution, show
lifetimes that are occasionally short (3 to 6 months). This, together with
differed oil production observed after the treatments, adversely affects
oilfield economics (Crabtree et al. 1999; Lawless et al. 1997). Differed oil is
by far the more detrimental of the two. It is caused by invasion of the aqueous
solution in the near wellbore, creating a highly water-saturated region where
oil flow is greatly impaired. This effect is commonly known in formation damage
literature as “water blocking” (Economides et al. 1993).
To overcome these problems, one of the many approaches reported in the
literature is the injection of oil continous squeeze treatments. These
treatments use either oil-soluble scale inhibitors (Wat et al. 1998a; Wat et
al. 1998b) or Emulsified Scale Inhibitors (ESI). The latter are the
subject of this paper, where scale-inhibitor brine solution is dispersed in a
continuous oil phase, forming what is known as a water-in-oil or “invert”
emulsion (Lawless and Smith 1998; Collins et al. 2001; Collins et al. 2002;
Jordan et al. 2002; Lawless and Smith 1999; Smith and Lawless 2000).
In this paper we present a brief literature review of previous work
published on ESI squeeze treatments, followed by the description of a new
invert emulsion formulation, developed and currently under study in our
laboratory.
ESI injectivity behavior and droplet retention mechanisms for this new ESI
formulation are discussed. The product is developed entirely with
biodegradable products, to comply with stricter environmental legislation
currently under way for the North Sea region.
© 2007. Society of Petroleum Engineers
View full textPDF
(
2,115 KB
)
History
- Original manuscript received:
24 October 2005
- Revised manuscript received:
13 June 2006
- Manuscript approved:
16 June 2006
- Version of record:
20 May 2007
View Cart
