Laboratory Experiments Of Well Testing For Fracture-cave Carbonate Gas Reservoirs

It is well known that there is a variety of reservoir space in fracrured-cave carbonate reservoirs.The flow mechanism in it changes from Darcy flow to pipe flow,which makes it very difficult to get to know the flow mechanism in it.Because of the strong heterogeneity in reservoir,reservoir parameters are difficult to be explained,which makes it extremely hard to develop.It is of great importance to calculate reservoir parameters for fractured-cave carbonate reservoir by well testing.In order to find out the law of fluid flow in the reservoir,this paper firstly analyzes the fracture-cave unit of single well in Tazhong condensated gas reservoir.On the basis of the fractured-vuggy unit,the fractured-cave reservoirs are divided into five typical fractured-cave systems,namely:well-cave type(the well is drilled directly on the cave),well-fracture-cave model(the well is drilled on fracture next to the cave),well-fracture-cave-fracture-cave model(double fractures and double holes in series),cave-fracture-well-fracture-cave type(double fractures and double holes in parallel),cave-fracture-cave(well)-fracture-cave type(compound model).According to the geometric similar,movement similar and dynamic similarity,the experiment parameters are deduced,which can reflect the characteristics of fractured-cave reservoirs.Based on experiment study,the parameters of fracture and cavity are explored on the influence of the well test curve,which verifies that it is feasibility to reflect the fractured-cave system underground by experiment in well testing.The cave is regarded as a spherical equipotential body while the flow in fracture is simplified as Darcy flow.Analytic solution is derived for five different types of fracture-cave carbonate well testing model.By comparing Stephfest numerical inversion with GWR numerical inversion method,nonphysical oscillations and numerical diffusion are eliminated and five different typical charts were got.By sensitivity analysis,the influence of fracture and cave parameters to the theoretical type curves were got,which presents the same trend as it is in the experiment.The deduced model can explain the fracture and cave parameters in experiment reasonablely,which verifies the correctness of the five kinds of theory.The five kinds of model in the paper provide a reliable guarantee for parameters of large scale fractured-cave carbonate reservoir.