Overflow Shut-in Water Hammer Control Study

The paper is a part of CNPC's science and technology program, which is "gas well pressure control system research under high pressure and high produce in complex condition".(The program NO. 03B2091200)When the additional gas influx occurs in the bottom of a well, we must close the well right now. The water hammer should be considered while close the well in order to prevent the water hammer pressure from wrecking the formation and the blow-out preventer (BOP). After analyzing factors impacting the water hammer, the paper set up the water hammer mathematic model, apply character line method and ADINA software to solve model. Then the theoretic calculation show that the atmosphere jar can decrease the water hammer pressure and the engineering meaning of research water hammer has been brought forward: On the one side, the water hammer is an important reference of closure method; On the other hand, the water hammer is helpful to the wellhead BOP choice.Firstly, The paper describes briefly the basic theories of current water hammer calculation including both water hammer mathematic model and calculative methods; calculative methods of the equation being scarcely precise. Moreover, detailedly analyzing factors impacting the water hammer. Those factors include elasticity module, pipeline size, gas content, solid grain content ,ect. The paper regard the gas content and solid grain content as the most important factor. As solid grain content rise, the pressure wave propagation velocity go up, however, as gas content rise, the wave velocity go down.Secondly, The paper present the new water hammer mathematic model including all kinds of boundary conditions based on closure well physical model. The water hammer mathematic model includes continuity equation and movement equation thinking of the friction in the process of producing water hammer pressure functions. Based on the correct water hammer mathematic model, applying character line method, to translate the differential equation group into character equation group, to count the character equation integral along with character line and at the same time to substitute the integral form for the difference form so as to make use of computer to carry through numerical value calculation of the water hammer pressure. The output are as follows : 1) "hard" shut-in > "half soft" shut-in and "soft" shut-in, the water hammer pressure decrease gradually; 2) the top of a well, the casing shoe and the bottom of a well the water hammer decrease gradually because of dissipation; 3) the gas can minish the water hammer pressure. Then the last calculative part of paper use ADINA software to solve mathematical model. The whole result show that the output of ADINA software is consistent to that of theoretical mathematical model.Finally, considering the measure about controlling the water hammer, the papercombining the other engineering, fearlessly apply the atmosphere jar to the well head assembly. Then the theoretic calculation show that the atmosphere jar can decrease the water hammer pressure. However, the well head assembly is too complex, whether this measure being appropriate need to be more considered.