Research On Hydraulic Pulse-chemical Deep Penetration Blockage Removal Technique In Low-permeability Reservoir

Low permeability sandstone reservoir has a large proportion in the oilfield, because its complex geology characteristics, reservoir density and strong heterogeneity,oil wells productivity are low and water wells inject difficulty. The conventional physical and chemical methods have great limitations in low permeability injection wells. Hydraulic fracturing can make water shutoff easily, conventional acidification is short in effective distance and time .Hydraulic pulse-chemical composite stimulation technique refers to the new-type technique that combines hydraulic pulse produced by vibration source with chemical treatment. Hydraulic pulse can prevent or inhibit the blockage formation near the sidewall or perforation, which is a dynamic blockage removal project. The combination of large-power pulse and chemical blockage removal agent can not only improve the chemical reaction effect but also increase the chemical reaction distance, which can promote the seepage and decrease or inhibit the blockage secondary formation.Thus, for mid-low permeability and extremely low permeability reservoirs, the composite blockage removal stimulation technique can clear the perforation effectively, remove near-wellbore blockage and the effect is far better than single reaction effect, making stimulation effect to be improved largely.This paper analyzes the injection well blockage reasons in Reservoir N₁-N₂¹, finding out the reasons of injection pressure increases and injectivity decreases are the influence of geological structure, water-sensitivity and speed-sensitivity.According to the actual situation of Gasi N₁-N₂¹ in Qinghai Oilfield, the experiments including corrosion experiment, anti-swelling experiment, corrosion inhibition experiment, core flow experiment and so on, are carried out, selecting the suitable acid systems: CH-59 and CMH-CMF multi-hydrogen acid systems.The hydraulic pulse-acidizing composite core flow experiments are conducted; the matching technique are set up; and the field tests are carried for 2-3 well times and the injection amount are increased by 10000m3.According to hydraulic pulse kinetic equation and acidizing equation, the superposition wave equation and acidizing model at hydraulic pulse condition are developed for the first time and the corresponding software are programmed to analyze the influence of distance, pulsing time, pulse frequency, pulse amplitude for seepage speed and acid concentration. The result illustrates that all the above factors have obvious influence; the acid penetration distance with hydraulic pulse is farther than that without pulse. These provide theoretical basis for the wide application of hydraulic pulse-chemical deep penetration blockage removal technique.