(29e) Naphthenic Acids in Oils with Different Contents of Asphaltenes

Naphthenic acids in oils with different contents of
asphaltene

Fenglou Zou, Huang Zeng,
Simon I. Andersen

Schlumberger, DBR Technology Center, T6N 1M9 Edmonton, Canada

Carboxylic acids (RCOOH), also known as naphthenic
acid in the oil field industry, is characterized by the presence of at least
one carboxyl group (-COOH). They are widespread compounds, occurring in
sediments and petroleums. Due to the structural
characteristics, naphthenic acids are considered as natural surfactants in
crude oil and believed to play a part in oil viscosity, emulsion stability,
reservoir wettability, and enhanced oil recovery by
alkaline flooding as well as corrosion. Therefore the knowledge of acid content
and acid structure may have a significant practical application potential. The
acid content in crude oils varies. One may speculate on the relationship
between crude API, asphaltene content and the content
of acids. As such there is currently no indication in the open literature of a
straight relation.

Two oils (A and B) containing different asphaltene contents were extracted with either ion exchange
resins (IER) or water. A (4% asphaltene), has higher acid
concentration than B (14% asphaltene). Obviously
higher asphaltene content does not mean necessarily
higher acid concentration. Figure 1 compares the speciation of acid composition
of the two oils using 2D GC/MS after methylation. B
contains more diacids and straight chain acids but less
aromatic acids and cyclic acids. The water extraction was found to yield
completely different acid distributions when compared to the IER extracted.
Both mono and diacidic compounds were detected. The diacids with two carboxylic acid groups could have
structure building potential leading to increased non-Newtonian behaviour.
Straight chain acids are known to act as surfactants at interfaces. More diacids were found in B compared to A
implying that higher asphaltene content could
indicate more complexity in the acids. Data from a range of oils will be
presented.

Fig. 1: Comparison of ion (m/z = 59) chromatograms of oil B 14% asp. (top) with oil A 4% asp. (bottom).
1: ethandioic acid, dimethyl
ester, 2: butanedioic acid, dimethyl
ester, 3: pentanedioic acid, dimethyl
ester, 4: hexanedioic acid, dimethyl
ester, 5: octanedioic acid, dimethylester,
6:nonanoic acid, dimethyl
ester 7: C₄H9COOH, 8: C₂₈H₅₇COOH