Discussion on the Disappearance of Transition Flow of Fractured Gas Reservoir with Pressure Transient Analysis

In recent years, more and more fractured gas reservoirs were discovered in the world. In general, fractured gas reservoirs are defined as formation with double porosity system, which is composed with fissure and matrix. In reservoirs with double porosity system, only the fissure system are connected with the wellbore and have relatively high permeability, matrix rocks have very low permeability, gas can flow into the wellbore only via fissures, and the flow process be divided into the flow in fissures, transition flow and the flow in the total system. But transition flow is not found in the process of well testing, which results in misapplication of development decision support and selection in gas field development program. In this paper, the influent factors of fractured gas reservoir for estimation are studied by models of single well simulation, and the simulated results are analysis by the method of pressure transient analysis. For example: the time of pressure build-up test, production time, wellbore storage coefficient,kv/kh,the reservoir boundary, the pressure precision, the porosity of matrix and fracture, the permeability of matrix and fracture, the thickness of formation(partial perforation),skin, water saturation etc. The results of simulation show that the disappearance of the transition flow is caused by many factors, which include that the time of pressure build-up test is short, production time is not sufficiently long, ,the vertical permeability is much larger than the horizontal permeability and the formation is perforated partially, the time of the reservoir boundary for pressure is short than the transition flow, the porosity of matrix is close to the porosity of fracture, the permeability of matrix much smaller than the fracture permeability, the pressure precision is low. The transition flow is not affected by the skin, the wellbore storage coefficient and water saturation, which cover up the radial flow in fissure system.