751-768－The fluid regime during fracturing of the Embla field, Central Trough, North Sea.pdf

Marine and Petroleum Geology 04 "0887# 640Ð657
The ~uid regime during fracturing of the Embla _eld\ Central
Trough\ North Sea
I[A[ Munza\\ K[ Idena\ H[ Johansena\ K[ Vagleb
a Institutt for ener`iteknikk\ P[O[ Box 39\ N!1996 Kjeller\ Norway
b Phillips pany Norway\ P[O[ Box 119\ N!3945 Tanan`er\ Norway
Received 09 September 0886^ revised 11 July 0887^ accepted 16 July 0887
Abstract
The deep Embla _eld\ located in the Central Trough\ North Sea\ represents the _rst oil reservoir in Paleozoic rocks to be developed
on the Norwegian shelf[ The reservoir consists of braided ~uvial and alluvial fan sandstones interlayered with ~oodplain:lacustrine
mudstones and volcanics and intrusives[ Extensive fracturing of the reservoir has led to the formation of numerous mineralised veins[
Three main types of mineralised fractures can be identi_ed] "0# early ic veins and veins which occur in and around ma_c
igneous rocks^ "1# carbonate!dominated veins^ "2# barite\ clay minerals and bitumen veins[ This article presents ~uid inclusion
evidence from fracture!_lling minerals\ suggesting that the fractures were important ~uid conduits of both petroleum and brine
migration[ The petroleum inclusion data are consistent with an undersaturated position[ A range in salinity between 12 and
01 wt ) NaCleq is found for the aqueous inclusions[ The variation in salinity indicates mixing between a high saline ~uid\ related to
evaporites\ and a ~uid with lower salinity[ Microthermometry data suggest that the fracturing events occurred at deep basinal levels\
at temperatures in excess of 099>C[ Þ 0887 Elsevier Science Ltd[ All rights reserved[
0[ Introduction roleum and brine migration in the Embla _eld\ Norweg!
ian North Sea[ The deep\ Paleozoic Embla _eld shows an
Fracturing of sedimentary sequences may involve sig! exceptionally high abundance of mineralised fractures[
ni_cant changes in the ~uid dynamics of a basin[ At the Petrography and temperature data from ~uid incl