Summary
Field engineers and reservoir modelers often question if equilibrium
conditions prevail downhole, and when do super(sub)saturation conditions exist.
This questioning is especially critical in designing seawater injection for
pressure maintenance caused by serious barite scale problems in
barium-containing formation water. This paper: (1) discusses the experimental
research on rock-brine interaction to determine if equilibrium conditions and
kinetics prevail, and (2) develops realistic seawater/inhibitor injection
schemes for scale control during seawater injection.
We have examined the question from three points of view: (1) thermodynamic
equilibrium, (2) mass transport kinetics, and (3) experimental testing of flow
through columns with or without scale inhibitors. If the reaction direction is
from undersaturated toward saturation, then equilibrium normally occurs
rapidly, being observed within approximately 5 minutes. When the reaction is
going from supersaturated to the equilibrium direction, such as during seawater
injection into a barium-containing formation, the precipitation reaction is
often slow (i.e., equilibrium is not observed after 10 minutes of contact time.
Both barite dissolution and precipitation rates on clean core material are
consistent with those reported in literature with a second order rate constants
for dissolution (≈ 30,172
L2∙mol–1∙m–2∙sec–1, 100ºC) and
precipitation (= 938
L2∙mol–1∙m–2∙sec–1, 100ºC).
The kinetics of barite formation can significantly slow down in the presence
of scale inhibitors, and the sulfate tolerance can be increased. The kinetics
of both barite dissolution and precipitation are poorly understood at the
present time. Combining sulfate reduction and scale-inhibitor application in
intelligent engineering design can significantly reduce the problems and costs
associated with seawater injection. Equations for the engineering design of
such treatment were derived from nucleation kinetics, inhibition efficiency,
and inhibitor adsorption and transport. Sulfate tolerance in the presence of
scale inhibitors is measured and compared with the prediction from nucleation
inhibition theory with excellent agreement. An innovative inhibitor treatment
by way of coreflood has been done as proof-of-concept and is discussed
herein.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
10 March 2008
- Meeting paper published:
28 May 2008
- Revised manuscript received:
2 October 2008
- Manuscript approved:
7 February 2009
- Published online:
23 July 2009
- Version of record:
28 September 2009
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