SOME EXPERIENCE IN SOFTENING THE OILFIELD WATERS BY ION
EXCHANGE FOR STEAMFLOOD OPERATION
James C. T. Chen, Manager
R. O. Engineering Department
Koomey Inc.
Brookshire, Texas 77423
SUMMARY
The needs for softening oilfield produced water for steamflood operations are ever increasing.
However, high total dissolved solids (TDS) level of produced water and stringent trace hardness
requirement of steamflood water render the processes such as single softening and ion exchanges
using strong or weak acid resins either technically or economically unfeasible. Furthermore, few field
data or guidelines exist forming the basis of process selection.
This paper proposes guidelines and/or limitations for the selection of the softening processes when
treating oilfield produced waters. These guidelines were developed based on some field experiences
with counter-current regeneration of two-stage series sodium zeolite softening. Influence of salt dosage and hardness on series softener performance was discussed. Salt dosage and quality were found
to be critical in softening high TDS water and less critical for low TDS water.
INTRODUCTION
Selection of viable ion exchange processes for use in softening water for oilfield steam generation
is governed mainly by the TDS of the water. These viable processes include: 1) single-stage zeolite;
2) two-stage zeolite; 3) single-stage zeolite followed by carboxylic polisher; and 4) lime soda softening
followed by carboxylic polisher. Single-stage zeolite softening with downflow regeneration has been
reported to be successful when the TDS of water is below 1,000 mg/1; two-stage zeolite has been
operated satisfactorily where TDS of the water is below 3,000. For TDS higher than 3,000 mg/1,
single-stage zeolite followed by carboxylic polisher and hot lime softening followed by carboxylic
polisher has also been successfully employed. Carboxylic polisher using the sodium cycle is the preferred process because the ion exchange proceeds rapidly and the capacity is not so sensitive to flow
rate and temperature as is the hydrogen cycle.
The estimated hardness leakage from zeolite softening was based on the TDS of the water and
salt dosage used for regeneration. Little information is available regarding hardness leakage attributable to the impurity of salt used for regeneration. Salt impurity becomes more critical when coun-
tercurrent regeneration of two-stage zeolite softening is utilized. Any hardness ions retained in the
bottom of the resin bed will leak out during the initial normal run. The objectives of this paper are
to:
1. determine ihe impacts of impurity salt on the softening capacity and hardness leakage from a two-stage
zeolite,
2. determine guidelines and/or limitations for selecting the softening processes when treating oilfield produced water for steamflood operation, and
3. suggest certain parameters used for designing the softeners.
THEORY
An equation for predicting the hardness leakage level has been developed and is presented below:
[B~,=7*(T^
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