Book Description

AbstractThe present thesis focusses on two main issues: (i) the development of a multi-phase simula-tion tool for the characteristics of tight-gas reservoirs, and (ii) the investigation of advancedstimulation techniques. The latter mainly implies the analysis of certain damaging mechanisms,as well as the derivation of general modelling guidelines for fractured wells and underbalanceddrilling.A special simulation tool is developed, realised in a Fortran-MATLAB coupling. The numeri-cal model is based on the control-volume method with finite differences. It accounts for inertialnon-Darcy effects, non-Newtonian fluid rheology and stress dependency of permeability via asimplified approach. The discretisation framework is fully unstructured, using the connectionlist approach and the common two-point flow stencil. Wells and boundary conditions can behandled very flexible in the code. Contrary to conventional treatment in simulators, wells arediscretely included in the simulator.Inertial non-Darcy flow and stress dependency of reservoir permeability are shown to affect theaccuracy of simulation models, despite low gas rates. Considering a realistic scenario, with non-Darcy flow and permeability (stress) dependent non-Darcy flow coefficients, stress dependencyof reservoir permeability and fracture closure, a total reduction of 40 % is possible in a 10 yearproduction period under realistic conditions. New type-curves are presented for non-Darcy flowin fracture and reservoir, allowing for the determination of non-Darcy flow related parameters.The stress sensitivity of tight-gas rocks is crucial when simulating such reservoirs. The stressdependency of the reservoir permeability impacts the productivity to a much higher degree thanthe fracture closure.A two-phase model is presented for the simulation of cleanup processes in terms of loadwater recovery. The fracturing fluid is treated as the water phase. The load water, causinghydraulic damage, hardly curtails productivity. To get considerable reductions in productivity,permeability in the fracture vicinity needs to be severely impaired. Due to the flow pattern,fractured wells are generally less sensitive against near wellbore damage than radial wells. Anenhanced three-phase cleanup model is presented for the investigations of the polymer gelcleanup, incorporating a yield power law rheology (the Herschel-Bulkley model). The combinedoccurrence of loadwater recovery including capillary forces and the gel cleanup, are investigatedfor the first time. First results indicate that both processes are only weakly coupled.A new simulation methodology is presented to investigate underbalanced drilling, taking intoaccount multi-phase reservoir flow with capillary forces. A sensitivity analysis points out that thedegree of water encroachment is the key factor for a successful UBD operation. Countercurrentimbibition, causing water encroachment is also analysed. Hydraulic damage turns out to be farmore pronounced in tight-gas formations.