The Transient Evolution Law Of Coupling Flow In Formation-Wellbore While Gas Drilling For Deep Tight Sandstone Gas Reservoir

With significant technical superiority in reducing and avoiding formation damage, improving penetration rate, boosting well productivity, and avoiding lost circulation etc, gas drilling has be used extensively in the exploration and exploitation of tight sandstone gas reservoirs in western and estern Sichuan and Tarim basin. However, gas drilling is usually used to improve the rate of penetration when the target reservoirs we dealt with are tight sandstone gas reservoirs. From2011to2013, gas drilling technology has been applied in three wells with tight sandstone gas reservoir as target formation in Tarim oil field, where higher production was obtained, which can be rendered as a big breakthrough of geological knowledge and technology progress, reaveling that gas drilling has the potential to play an important role in the high-efficient development of tight sandstone gas reservoir. However, owing to the complexity of engineering geological conditions with higher pressure and productivity, there are still many fundamental theory and key technology problems needed to be investigated. In gas drilling, the flow law and multi-field coupling of gas seepage, transient flow in fracture, transient wellbore flow are extremely complex, By now, there is not a clear understanding of the transient behavior of pressure, velocity, temperature, and their decisive factor, which are very important for well control and reservoir characterization while gas drilling. It is necessary to do further study on the full transient flow characteristics of coupling formation-wellbore during gas drilling in the deep tight sandstone gas reservoir.The main research findings are shown from fluid mechanics and thermodynamics as follows:(1) Mathematical models of steady flow, transient flow and full transient flow considering the energy equation in the wellbore were proposed and solved. The transient evolution law of pressure, flow rate and temperature in wellbore considering the thermodynamic influence has been revealed for different conditions.(2) According to the causes and geometry of fracture, transient mathematical models of equivalent circular fracture without gas source from matrix were proposed and solved, based on the laws of mass conservation, momentum conservation and energy conservation. The transient evolution law of pressure, flow rate and the temperature in equivalent circular fracture have been revealed.(3) Mathematical models about the transient flow of coupling matrix-fracture with gas source from matrix were proposed and solved. The transient evolution law of pressure, flow rate and the temperature in equivalent circular fracture have been revealed, discussing influencing of energy equation, matrix properties (K) and fracture geometry.(4) The models of the transient flow of coupling matrix-fracture-wellbore considering the energy equation with gas source from were proposed and solved? the transient evolution law of pressure, flow rate and the temperature for the gas in fracture and wellbore have been revealed, while the deep tight sandstone gas reservoir is opened using gas drilling technology.