Experimental Study On The Characteristics Of Water Hammer On Annular Space In Petroleum Engineering

In petroleum engineering, the liquid flow through the casing annulus occurs in the process of water injection to improve oil recovery and well washing. Mechanical failure or electric motor power-fail could make the annulus fluid lose dynamic instantly, inducing the water hammer in the long pipeline. The water hammer due to dynamic loss of annulus fluid brings serious problems to oil production safety and surrounding environment, so it is necessary to investigate this phenomenon. At present, research on the fluid mechanics of annulus mainly focus on the governing equations, analytical method, and boundary form effects on liquid fluid of steady/unsteady eccentric/concentric annulus flow, including the spiral flow in the eccentric annulus, the inner tube fluid planetary motion and the circumferential reciprocating motion of the unsteady flow. The studied fluid includes Newtonian fluid, power-law fluid, etc. However, the characteristics of water hammer due to dynamic loss of annulus fluid is still an open problem.By combining the annular flow channel structure, the formula for calculation of water hammer wave speed was derived in the annular flow channel, and the friction term in the formula was analyzed. Then, water hammer due to dynamic loss of annulus in positive injection, commingled injection, inverse injection in vertical shaft device and commingled injection in horizontal well device was simulated, and the characteristics of pressure and flow field were analyzed by PIV and intelligent digital dynamic pressure acquisition system. The causes of water hammer were analyzed with the attenuation process of flow velocity in casing annulus and characteristics of vorticity field. Meanwhile, water hammer wave velocity formula was analyzed by comparing computed and measured wave speed. Furthermore, pressure and flow field parameters of annular helical water hammer were collected by PIV and transient pressure acquisition system, and the rotation of spiral flow in the annular flow channel was measured by a vortex rotation angle measuring instrument (declared national patent) designed based on the USA reference standards, and then the water hammer characteristics of different rotation stall helical flow in an annular were analyzed. Finally, the characteristics of reciprocating oil pump quick closing and opening water hammer and valve quick opening water hammer were investigated by experimental installation. Meanwhile, the concept of water hammer number was introduced to analyze the characteristics of reciprocating oil pump water hammer valve in different operation modes and their influences on fluid flow in an annular flow channel.The results show that the water hammer that occurs in positive and commingled injection fluid produce might induce the pipe wall pressure transient imbalance, and the pressure difference can reach up to hundreds of times. Casing annulus inner and outer walls, oil pipe inner wall water hammer pressure is balanced during inverse injection. The positive injection rod pumping wells annulus liquid flow attenuation is faster than the speed of tubing, pressure attenuation is slower than the tubing, and the dynamic loss has an effect on annulus fluid flow in the tubing flow. For the horizontal well commingled injection, water hammer pressure in an annulus flow channel is large, and the water hammer pressure and velocity attenuation is fast. Besides, the annular water hammer pressure of outer wall is greater than that of inner wall, and the water hammer pressure decay of inner wall is faster than that of outer wall.When water hammer in eccentric rod pumping wells annulus and oil pipe occurs simultaneously, pressure difference between inner and outer wall of rod pumping wells annulus increases with the eccentricity, and in the inner and outer walls, as well as both sides, water hammer pressure double imbalances. The larger the eccentricity is, the smaller the flow velocity is, and the faster the annulus flow velocity attenuation is. When water hammer only occurs in the annulus fluid flow stall, the small eccentricity produces big pressure difference between inner and outer walls, and the attenuation of annulus velocity in small flow channel increases with eccentricity. When water hammer only occurs in the tubing flow stall, pressure difference between inner and outer walls of the pipe is big.When the annular flow channel spiral flow water hammer stall occurs, the flow velocity attenuation in the annulus on both sides of channel is non-synchronously symmetrical. The section velocity and attenuation of shock wave change with vortex rotation angle, and the section of vorticity is not completely attached to the wall, which decreases with the increase of vortex rotation angle. The pressure difference between inner and outer walls also decreases with the increase of vortex angle.When reciprocating oil pump stalls, valve quick opening and closing produce water hammer. In this case, water hammer pressure is small, and the rate and duration of decay is pretty low, but the hammering number on each cross-section is relatively large. When the valves are closed quickly, water hammer pressure is bigger, the decay of hammering number is faster, the duration of decay is longer, and hammering number is smaller.