Geochemical Aureoles Around Oil and Gas Accumulations in the Zechstein (Upper Permian) of Poland: Analysis of Fluid Inclusions in Halite and Bitumens in Rock Salt

Abstract

Fluid inclusions in halite and bitumens in rock salt in Upper Permian Zechstein evaporites inWest Poland were studied in locations where the evaporites lie above oil and gas reservoir rocks. The samples were taken from halite intercalated within the Basal Anhydrite; this unit lies above the Main Dolomite which serves as both source rock and reservoir. Samples came from a depth of 2.3-3.2 km. A characteristic feature of the fluid (gas-brine) inclusions was their high methane content together with the occasional presence of bitumen globules of near-spherical form. Geochemical analyses of the bitumen in bulk samples of rock salt (including content and distribution of n-alkanes and isoprenoids, and carbon isotope ratios) suggest an algal origin, similar to that of the oil in the underlying source rocks. For comparison, we studied fluid inclusions in halite from Zechstein evaporites in northern Poland, where hydrocarbon accumulations do not occur in underlying strata and where mostly single-phase (brine) inclusions with a low methane content have been recorded. However, published data indicate that similar inclusions to those occurring in the Zechstein of West Poland (comprising brine with a high methane content, bitumen films and/or oil droplets) are present in other salt-bearing sequences, where their origin is related to the thermal degradation of organic material dispersed within the salt itself. Accordingly, such fluid inclusions in an evaporite succession can only be considered to form a geochemical aureole where the bitumens in the rock salt (including those in the fluid inclusions in halite) can be compositionally linked to those in the associated oil accumulation.

Hydrocarbon potential of the Zechstein Main Dolomite (Upper Permian) in western Poland: Relation to organic matter and facies characteristics

“…This conclusion is consistent with observations of e.g., Hunt (1961Hunt ( , 1972, Gehman (1962), Tissot and Welte (1984) and Bond (1986) concerning organic matter in carbonates. These authors drew attention to high petroleum efficiency of carbonate rocks, which is additionally increased in the Ca2 due to perfect sealing by evaporites (Kosakowski et al, 2003;Kotarba and Wagner, 2007;Kovalevych et al, 2008).…”

“…2). At the platform the LST sediments occur also in the upper part of the Main Dolomite and are represented by sabkha and salina facies known from the lower part of the Basal Anhydrite (A2) where they form the 4th Zechstein Sequence Boundary (ZSB4) Kovalevych et al, 2008;Peryt et al, 2010b). The Ca2/A2 transition is gradual and marked by fine deposition cycles corresponding to small-scale sea level oscillations.…”

Calculation of salt basin depth using fluid inclusions in halite from the Ordovician Ordos Basin in China

“…The hy dro gen data in the gas mix ture are not in for ma tive due to the abil ity of hy dro gen to dif fuse freely through the crys tal struc ture of the min eral. The sources of these com po nents in the bot tom brine of the salt ba sin were bio chem i cal pro cesses and the at mo sphere (Weiss, 1969;Kovalevych et al, 2008). The ab sence of ox y gen in the gas mix ture is as so ci ated with ox y gen con sump tion dur ing chem ical and bio chem i cal ox i da tion.…”

Новые Данные По Геохимии Газов Калийных Месторождений

“…Иная картина наблюдается для газовожидких включений из галита нижнепермских эвапоритов польского цехштейна, залегающего на глубине 2,3-3,2 км; предполагается как его связь с нижележащими месторождениями нефти и газа, так и аутигенное образование [13].…”

“…Морачевский с соавторами [6] предполагал их захват во время садки солей из рассолов. Значительная часть исследователей связывала возникновение газов с преобразованием сингенетично захваченного органического вещества [1,4,9,13], химического [2] или радиогенного [8] разложения карналлита. Известно также устное высказывание П.А.…”