Simulation of the production behaviour of hydraulically fractured wells in Tight Gas Reservoirs
Hydraulically fractured wells enable gas production from tight gas formations. However, productivity frequently remains below the predictions. Deficits in the simulation models and their applicability for tight formations can be considered as major reasons for that. Hence, customisation of the simulation techniques regarding the specific conditions in such formations with the derivation of the corresponding petro-physical functions is the major objective of the investigations. Different approaches for direct and inverse (history matching and optimisation) numerical modelling hydraulic fractures using both commercial and in-house simulators were applied and enhanced in some critical aspects and functionalities. To ease the workflow of hydraulic fracture simulation by automatically setting up an appropriate simulation model, a support tool was developed which provides the coupling of commercial fracturing software with reservoir simulators. Specific physical aspects, e.g., NonDarcy-flow, stress dependency of permeability and fracture closure, were considered in terms of their impact on the productivity. Potentially, productivity losses up to 40 % are possible if disregarded in the simulation. Special attention was paid to the fracture fluid cleanup process. Condition were determined where hydraulic and mechanical damage impair productivity. The relationship between in-situ stress and both absolute permeability and relative permeability functions was analysed in the framework of laboratory investigations. It turned out that the impact of in-situ stress on absolute permeability is prior in tight formations. Five typical facies types were investigated in terms of their suitability for stimulation treatments.