Oil Well Abrasive Jet Slotting Technology And Its Theoretical Research

Oil well downhole abrasive jet slotting technology is a highly new technology for oil well production increasing, injection increasing of water injector and improving oilfield recovery which has been used in Daqing Oilfield, Shengli Oilfield and Liaohe Oilfield, etc. with very good results. Mechanism and mechanical model of abrasive jet slotting are studied in the paper so that theory of abrasive jet slotting for oil (water) well is established and theoretical support is provided for continuous improving and technical parameter selection of the technology. In downhole slotting, two kinds of materials with different properties of metal and rock need to be slotted, so this research is also suitable for common abrasive jet slotting.Abrasive jet is a jet formed by the mixer of a small amount of abrasive particles and water. In view of small grain diameter, low mass and volumetric concentration, even distribution and high flow rate and flowing with water for abrasive particles, it can be regarded as solid-liquid two phase flow of balanced sparse flow. Based on basic differential equation of solid-liquid two phase, basic equations for equivalent monophasic fluid of solid-liquid two phase flow are obtained with continuous medium dual fluid model so that solid-liquid two phase fluid flowing can be studied with mechanism and method for monophasic fluid mechanics. Turbulent equations are established with methods of polar coordinates and averaging time and turbulent equation is simplified as correspondent boundary layer equation, that is, free abrasive jet differential equation of turbulent circular section through magnitude comparison. Similar solution and momentum integral solution for differential equation of free jet of abrasive circular turbulent are derived and flow rate distribution for circular free abrasive jet, axial flow rate on axial line and on way variation for cross section are obtained.According to surface simulation test and theoretical analysis, slotting of metallic casing by abrasive jet is realized by the acting force caused by contact of abrasive particles in abrasive jet and internal surface of metallic casing. As contacting area for abrasive particles and metallic casing is small, even the acting force is not large, contacting stress formed in contacting region is still large. Since casing is made of metallics, as contacting stress exceeds contact shear strength, material in contacting region is damaged and scaled to form depression. Depressed areas are formed continuously by the action of a large amount of abrasive particles on the material surface to form slots. Therefore, metallic casing is slotted by abrasive jet when shear stress formed by contact of high-speed of abrasive particles and casing is damaged. As a matter of fact, mechanical model for slotting of metallic casing by abrasive jet is established due to contacting problem in elastic mechanics.Rock is slotted by abrasive jet through slots. Restricted by the bottom and two sides of slots, surrounding fluid indrafted into the jet is reduced greatly, so flow rate of the jet slows down. Differential equation for abrasive jet motion is established by considering solid-wall frictional resistance and on way variation of axial speed on axial line for abrasive jet through slots is obtained by combination of similar solution of differential equation and dimensional analytical solution. Rock is fragile material with tensile strength only one fraction of shear strength and compressive strength. So rock is damaged by tensile wave caused by unloading of a large amount of abrasive particles which impact rock surface continuously at a high speed and slotted by debris scaled from rock surface. Mechanical model of rock slotting by abrasive jet is established on the basis of rock dynamics, fluid mechanics and wave propagation theory. And oil well abrasive jet slotting theory is formed by combination of mechanical model of rock slotting by abrasive jet and mechanical model of casing slotting by abrasive jet. Calculation of the example is similar to surface simulation slotting test which can be applied in engineering. Finally, mechanism of slotting simulation and selection of technical parameters for abrasive jet slotting are analyzed.