Well Test Analysis Of Multi-layered Gas Reservoir

In order to acquire economic gas productivity, most gas reservoirs would adoptcommingling production and Sebei Gas field is one of the most typical examples,which has large span on vertical zone, evident difference of physical properties andformation thickness between layers. Number of single well perforation layers isabout5on average in this field. At present, accordingly, there is more well testinterpretation for multi-layered gas wells than single-layer models. However, due tothe heavy heterogeneity between layers, the difficulty of interpretation formulti-layered wells is increased. Consequently, it is significant for us to study theflow mechanism of multi-layer reservoirs and find better interpretation methods sothat multi solution phenomenon is reduced and reliability of well test analysis can beenhanced.In this thesis, the flowing mathematical model for multi-layer gas reservoirs isestablished by introducing dimensionless definitions. By using Laplace transform,production rate and pressure equations as well as corresponding change curves forthem are obtained. It is shown by numerical inversion results that the productivity andpressure of single layer all continue to change rather than stand still in comminglingproduction.Multi-layered model shows that the profile of well test curves can be affected bypermeability, storativity ratio, initial pressure as well as boundary situations. Whilepermeability and storativity ratio have weak influence, initial pressure and boundarysituations can exert relatively stronger effect on the curves.The accurate interpretation can be performed by using multi-layer well testmodel established after the acquirement of production rate and pressure data of singlelayers, and thus the physical parameters for each layer can be obtained. It should benoted that we should abide by the following principles, for the same well, its physicalproperties, the geometrical characteristic of drainage area, formation permeability orformation capacity in flowing zone should remain relatively stable when averagereservoir pressure changes little.Aimed to the gas wells which have no layered testing pressure and productionrate while have commingling buildup test data, it is presented in this thesis that thereasonable combination of single layer well test model and faults can be approximately used to explain multi-layered flowing phenomenon. This method canobtain average formation physical parameters and reduce multi solution as well asblindness of choosing models. It is shown by the application in Sebei Gas Field thatthis approximate treatment can have a good applied prospect.