Non-Destructive Barite Cement in Upper Jurassic Sandstones, Danish Central Graben, North Sea

Abstract

Barite is a late diagenetic cement that is commonly occurring in some of the marine Upper Jurassic sandstone units in the Danish Central Graben, North Sea. Typically, barite is sparse and probably formed at deep burial as Ba²⁺ and SO₄^2- became concentrated in the formation water. Occasionally, barite cement has been reported from the North Sea sandstones in higher abundances and then as a destructive cement severely affecting the reservoir properties, except when it occurs as rosettes.

In marine Upper Jurassic sandstones in the Hejre Field in the Danish Central Graben, the barite cement occurs as rare fracture fillings, minor fillings of shells and common rosettes. Permeability destruction is severe where barite cement occurs as fracture fillings or in combination with calcite cement associated with shell lags. Fortunately, these appearances are rare and consequently have little influence on the overall reservoir quality. Porosity and permeability reduction are minor in sandstones with barite rosettes, despite the barite cement amounts to more than 15% of the mineralogical content. The patchy occurrence of the barite cement may reflect the distribution of fossil fragments, which may have acted as nucleation points. The barite rosettes function as large grains around which the fluid easily flows so the permeability is almost unaffected.

Abundant barite cement in the North Sea area is typically associated with faults and fluids derived from deeper, commonly Permian sediments and possibly Triassic sediments, and this cementation is destructive for the reservoir quality. Proximity to faults, fluid flow along deep seated faults and composition of the fluids may be crucial for the type and distribution of barite cement and hence its effect on porosity and permeability.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018