The Groningen Gas Field: A Case History of the Development of a Giant Gas Field

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Abstract
The Groningen Field is a major energy source for western Europe. Field development is characterized by grouping of wells in clusters of 8 to 11 wells with a gas-treating plant. To facilitate development planning, an integrated computer model was developed that comprised a reservoir simulator, a well-cluster model, and a dehydration-plant performance model. performance model. Introduction The Groningen gas field was discovered in 1959, when Well Slochteren 1 (SLO) was drilled. We found that the Slochteren sandstone (Rotliegend formation) was gas bearing. In early 1960, Well Delfzijl 1 (DZL) was drilled about 20 km from Slochteren . We found that the same formation was gas bearing and had the same gas composition. Although pressure buildup surveys in these two wells indicated the presence of large volumes of gas, interpretation of seismic data showed the two accumulations were separate.It was not until 1963, after reinterpretation of the seismic data, that the various accumulations encountered were recognized as one huge gas field. extending for more than 200,000 acres (800 km2). The northeastern part of the field extends slightly offshore into an area of part of the field extends slightly offshore into an area of common interest for The Netherlands and Germany.Proven reserves at the time were 40 × 10(12) cu ft (1100 × 10(9)m3), less than the proven reserves existing Jan. 1, 1978 [50 × 10(12) cu ft (1400 × 10(9) m3)], after 15 years of production. The estimate of original gas in place in the Slochteren sandstone is about 90 × 10(12) cu place in the Slochteren sandstone is about 90 × 10(12) cu ft (2500 × 10(9) m3). Material-balance calculations indicate an expansion drive.Initial development was limited to the southern part of the field, where the complete reservoir sand was gas bearing. The high reservoir permeability allowed the wells to be grouped in clusters to serve one gas-treating plant. plant. Rapid market growth and increased off-take from the southern area caused pressure differences across the field (Fig. 1). At the end of 1969, reservoir simulation studies showed that restricting off-take to the southern part of the field would result in considerably lower average wellhead pressures, compared with development of the entire field. Because lower tubinghead pressures would lead eventually to early installation of compressors, the new clusters necessary to meet capacity requirements were drilled in the central and northern part of the reservoir. The reservoir simulator was an indispensable tool for these optimization studies.To date, 28 clusters with 283 producing wells and 16 observation wells are spread over the field (Fig. 2). Total installed capacity is 18.7 × 10(9) cu ft/D (530 × 10(6) m3/d). In 1977, about 2.9 × 10(12) cu ft (83 × 10(9) m3) gas was produced.The Groningen Field is a major energy source for western Europe. It is very important that the volumes and capacities agreed upon in delivery contracts can indeed be supplied. To predict the capacity of the field, a simulator was developed in 1970. This planning tool included a treating unit/compressor model. For a given off-take pattern, various alternatives for drilling and construction can be evaluated to find the most economical development plan. Geology The main reservoir is the Slochteren sandstone, which is the lower part of the Rotliegend formation. P. 815

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