The Fault Block Model was designed for the devel-opment of gas production from Sleipner Vest. The reservoir consists of marginal marine sandstone of Hugine Formation. The structure is dome shaped and highly faulted with good reservoir productivity. Based on geological interpretation, location and extent of faulting in the reservoir was carried out and the effect of faulting as flow barrier was evaluated. Internal cross-flow communications between adjacent fault blocks defined by throw of faults were established.

The model redefines individual fault block traps in terms of block volume and cross-flow probability to adjacent blocks and estimates the number and lo-cation of wells required for optimum recovery of the gas reserves. The model predicts the corresponding well coverage, from which production profiles are calculated.

Modelling of highly faulted and compartmentalized reservoirs is severely impeded by the nature and extent of known and undetected faults and, in particular, their effectiveness as flow barrier. The model presented is efficient and superior to other models, for highly faulted reservoir, i.e. grid based simulators, because it minimizes the effect of major undetected faults and geological uncertainties. The geological interpretation and its uncertainty is minimized using fault block volume and cross-flow probability, which subsequently may translate into gas production profiles. The geological uncertainties are carried through in the model by error propagation techniques.

In this article we present the Fault Block Model as a new tool to better understand the implications of geological uncertainty in faulted gas reservoirs with good productivity, with respect to uncertainty in well coverage and optimum gas recovery.

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