Abstract A review of recent Triassic research across the Southern Permian Basin area demonstrates the role that high-resolution stratigraphic correlation has in identifying the main controls on sedimentary facies and, subsequently, the distribution of hydrocarbon reservoirs. The depositional and structural evolution of these sedimentary successions was the product of polyphase rifting controlled by antecedent structuration and halokinesis, fluctuating climate, and repeated marine flooding, leading to a wide range of reservoir types in a variety of structural configurations. Triassic hydrocarbon accumulations form an important energy resource across the basin, not only in the established Buntsandstein fairway but also in Rogenstein oolites and Muschelkalk carbonates. In addition, sand-prone sections in the Late Triassic, such as the Schilfsandstein, have the potential to be hydrocarbon reservoirs. Several Triassic intervals are now the focus for developing geothermal projects. A detailed understanding of Triassic reservoir quality and distribution is one of the main keys to efficiently unlocking the geothermal and remaining hydrocarbon potential across the basin.

Abstract Enhancing recovery of the remaining gas in ageing fields presents a commercial opportunity. As such, NAM took the decision to apply on-site generated N 2 injection for the first time. The De Wijk gas field was selected based on size and geological setting, allowing the demonstration of N 2 flooding of depleted gas in diverse reservoir types, as well as testing the efficiency of residual gas sweeping in the watered-out reservoir. De Wijk is one of the oldest onshore natural gas fields in The Netherlands, having produced c . 15 Bcm (billion cubic metres) of high calorific gas with a natural N 2 content of 5–11% for more than 60 years, bringing it close to the end of field life. Enhanced gas recovery in this field would extend the field life and that of the Ten Arlo gas-processing system, thereby also lengthening tail-end production of other connected fields. In De Wijk, the existing 35 wells were used as dedicated injectors and producers. The production rates from the latter are used to help better understand reservoir flow behaviour. Integration of geological analysis and available production data helped to implement the N 2 enhanced gas recovery technology in this mature field. Two processes of enhanced gas recovery were tested: a gas–gas displacement in the depleted gas leg (Nitrogen Assisted Depletion Drive: NADD); and gas displacing residual gas in the water leg (Nitrogen Enhanced Residual Gas: NERG). Observations after 1 year of N 2 injection showed that planned v. actual performance of the NADD technology is comparable with an increase in production of 100 000–160 000 Nm 3 /day (normal cubic metre per day). NERG application restored a watered-out well; however, further investigation of this application is required. It is demonstrated that a detailed geological understanding of, for example, permeable Rogenstein oolite intervals and the lateral connectivity of internal high-permeability streaks in Volpriehausen sandstones is crucial to the successful application of enhanced gas recovery techniques in such ageing fields.

Abstract The combination of sedimentological and diagenetic data is important for the characterization of carbonate pore systems. This is particularly true for carbonates that were affected by meteoric diagenesis during sub-aerial exposure, for instance at sea-level lowstands. This diagenetic environment is commonly believed to be associated with increases in porosity, permeability and pore-throat diameters. Using data from three localities, improvement or deterioration of reservoir parameters below karst unconformities were analysed with a three-fold approach. In the first step, meteoric dissolution was characterized and early to late diagenetic products were described. In the second step, sedimentological and diagenetic data were converted to petrophysical data. In the third step, modelled climate data, in particular the occurrence of monsoon cells, in conjunction with other control mechanisms, were considered to understand the processes that controlled meteoric dissolution and later pore infill. Three case studies were analysed: (1) Lower Triassic oolites (sedimentary rocks dominated by ooids) and microbialites of the Calvörde Formation (Buntsandstein Group, Germany); (2) stacked shallowing-upward cycles of carbonate platform deposits in the Middle–Upper Triassic Mahil Formation (Arabian plate, Oman), capped by palaeosols; and (3) an Upper Triassic coral patch reef and overlying strata (Adnet, Salzburg region, Austria). Data integration allowed the establishment of three scenarios of significantly different processes related to meteoric diagenesis below unconformities: (1) increase of porosity and permeability and their preservation through time; (2) increase of porosity and permeability and subsequent pore system occlusion; and (3) decrease of porosity and permeability and creation of a barrier for pore fluids. Knowledge of the time span involved in meteoric diagenesis and the nature of the climatic regime helped to explain the origins and control mechanisms of the meteoric pore systems. The study provided evidence that a well-connected, large karst system, typical of a humid climate, is likely to be sealed subsequently by sediment and cement. Under arid climatic conditions, tight palaeosols developed at the unconformity and small karst pore systems developed which had the potential to remain open during basin evolution. Depending on the aforementioned parameters, carbonates affected by meteoric diagenesis may either become tight rocks or reservoirs.

Abstract Germany has an enormous number of different carbonate rock units, which vary widely in their geological age and sedimentary depositional environment. Limestones quarried from these exposures have a wide range of usages and applications, such as dimension and ornamental stones, floor tiles and panelling, and for use as paving stones and massive stones. Since antiquity, limestones were used as building materials in areas where they were naturally available and abundant. Limestones exhibit a relatively good weathering resistance, which is mainly controlled by the mineralogical composition and the rock structure. The susceptibility of limestones to weathering and alteration is only secondarily related to the stone's contact with rainwater and its exposure to frost. In this situation the pore space is the main controlling factor. Industrialization and the subsequent increase in air pollutants, which started at the end of the nineteenth century, led to the formation of dark and unsightly crust deposits on the limestones surfaces. These crusts, being the result of man-made activities, are the main weathering problem for carbonate dimension stones.

Abstract Corvette is a small prolific gas reservoir with reserves of 211 BSCF located on the Indefatigable Shelf in the Southern North Sea. The reservoir is the Permian Rotliegend aeolian sandstone, capped by Zechstein evaporites and sourced from the Carboniferous Coal Measures. The structure is a 'pop up' between the Gawain and Baird Fields. The field was discovered in 1996 and brought on production in 1999, with gas being evacuated via the Leman Field to the Shell/Esso Bacton gas terminal.