25th International Meeting on Organic Geochemistry IMOG 2011

P-348
Distribution of tetraprotic (―ARN‖) acids in different oilfield
deposits determined using high temperature gas
chromatography and liquid chromatography-electrospray
ionisation mass spectrometry
Paul Sutton 1 , Steven Rowland 1 , Ben Smith 2
1 University of Plymouth, Plymouth, United Kingdom, 2 Oil Plus Limited, Newbury, United Kingdom
Regioisomeric mixtures of C80 tetraprotic (―ARN‖)
acids with 0 - 8 cyclopentyl rings are regarded as the
principal organic components in calcium naphthenate
deposits encountered in some oilfields [1,2] . These
compounds are H-shaped with an acid group at the
end of each ‗arm‘ (eg Fig 1) and have the generic
formula CnH(2n-6)-(2R)O8 (n = carbon number, R =
number of rings), range in molecular weight from
1243 – 1227 Da at 2 Da intervals for 0 – 8 rings,
respectively, have z-numbers from -6 to -22 at -2
intervals (for 0 – 8 ring, respectively) and double bond
equivalence of 4 - 12 DBE ( 0 – 8 ring, respectively).
To date, most of the research into this family of
tetraacids has been directed towards their
involvement in deposit formation [eg 3] . Besides interest
in the role of C80 tetraprotic acids in deposit formation
they are also of geochemical interest as they possibly
constitute a biomarker signal from parent oil
reservoirs.
H
O
O
H
O
O
O
O
Fig 1. Structure of C80 tetraprotic acid with 6 rings [1]
H
O
O
H
We have isolated the C80 tetraprotic acids from five
deposit samples, three from different North Sea
locations and two from different West African
locations. Isolated acids were converted to their
methyl esters and the relative distribution in different
deposits determined using high temperature gas
chromatography (HTGC) and identification using
liquid chromatography coupled with electrospray
ionization-mass spectrometry (LC-ESI/MS).
Typically all deposits contained C80 tetraprotic acids
as major constituents with 2 – 8 rings, however the
distribution by ring number varied between deposits.
The C80 tetraprotic acid with 6 rings dominated all
deposits (~45 – 50%; eg Fig 2) except one from the
North Sea which contained higher amounts of 7 and 8
ring compounds (36 and 37%, respectively; Fig 3).
Distributions of other homologs varied to a lesser
extent.
response (pA)
300
200
100
2R
3R
4R
5R
6R
0
35 36 37 38 39 40 41 42
7R
retention time (min)
Fig 2. HTGC chromatogram of C80 tetraprotic acid
methyl esters from a West African deposit
response (pA)
300
200
100
4R
5R
6R
8R
8R
7R
0
35 36 37 38 39 40 41 42
retention time (min)
Fig 3. HTGC chromatogram of C80 tetraprotic acid
methyl esters from a North Sea deposit
Identification of the original source of C80 tetraprotic
acids in oilfield deposits, whether from: novel extant
reservoir archaeal lipids, degradation products of
archaeal ether lipids, or produced by oil degrading
archaea as biosurfactants [4] , remains unresolved.
However, we have demonstrated the varied relative
distribution of C80 tetraprotic acids in different oilfield
deposits.
[1] Baugh et al. (2005) SPE93011
[2] Sutton et al. (2010) Rapid Commun. Mass
Spectrom. 24, 3195-3204
[3] Shepherd et al (2006) SPE 100517
[4] Lutnaes et al (2006) Org. Biomol. Chem. 4, 616-
620
479