Geology of the Groningen field – an overview

Abstract

After more than half a century of production and with some 350 wells, the Groningen gas field must be one of the best-studied gas fields in the world. Initially, it was considered to be relatively simple and behaving like one big tank. Now that it is entering a phase of declining production it has become clear that many subtleties are not fully understood yet. Prediction and management of subsidence and induced earth tremors require a detailed understanding of the field geology. In addition, an optimum gas recovery is only possible if details of, for example, reservoir quality distribution and faulting, that did not appear relevant before, are well understood.The large Groningen field comprises a structurally high block during much of its history, probably already from Devonian times onwards. The desert sandstones of the Rotliegend reservoir exhibit a strong south-to-north proximal-distal relationship. Whilst diagenesis has in many fields led to deterioration of reservoir properties, this effect is small in the Groningen field. The field is dipping to the north, and bounded by a series of normal faults in the west, south and east. Almost all faults are normal extensional faults, but locally inverse reactivation has led to small pop-up structures.Reactivation of older faults must have resulted in oblique movements along most faults.The challenges for future development of the Groningen field are immense. Managing the risks associated with induced seismicity and recovery of the remaining gas will continue to require an increasingly detailed knowledge and understanding of its geology.

Nucleation and Arrest of Dynamic Rupture Induced by Reservoir Depletion

“…The ~50‐m‐thick Ten Boer formation above the Rotliegend consists of clays and sandy material, which may have a higher horizontal stress due to creep (Sone & Zoback, ). The Triassic overburden (Zechstein Group) overlying the Groningen Slochteren sandstone and the Ten Boer is composed of a basal anhydrite and carbonate section of 50 m thick, overlain by hundreds of meters of rocksalt (e.g., de Jager & Visser, ). Creep of salt relaxes shear stresses and will create a near‐isotropic state of stress over geological time, that is, a stress ratio K 0 of 1 and an initial shear stress τ 0 = 0 (e.g., Haug et al, ).…”

“…Faults continue below the reservoir for at least several hundreds of meters into the Carboniferous underburden (Kortekaas & Jaarsma, ), which is composed of a tilted succession of shales, silts, and sandstone beds intercalated with coal seams (de Jager & Visser, ). No stress measurements have been conducted in the underburden.…”

Temperature and Gas/Brine Content Affect Seismogenic Potential of Simulated Fault Gouges Derived From Groningen Gas Field Caprock

“…In the Groningen gas field, the top of the reservoir system, that is, the Slochteren sandstone and overlying Ten Boer claystone, is saturated mainly with gas (mostly methane with~14 % nitrogen (De Jager & Visser, 2017;Stauble & Milius, 1970)) alongside connate brine (the connate water content in the reservoir varies between 7-25 % (Burkitov et al, 2016)). Faults that cut through the basal Zechstein and into the reservoir (including those that juxtapose the reservoir against the overlying basal Zechstein caprock and thus incorporate anhydrite and carbonate gouges derived from the caprock) are therefore expected to be saturated with a mixture of CH 4 and brine.…”

Numerical and experimental simulation of fault reactivation and earthquake rupture applied to induced seismicity in the Groningen gas field

“…At the time of its discovery in 1959, the Groningen gas field was the largest onshore gas field in the world with an initial gas in place (GIIP) estimate of 2100 BCM. The geology of the field is described in detail by de Jager & Visser (2017). The main reservoir rock is the Slochteren Formation (ROSL) of the Upper Rotliegend Group (Permian Age).…”