The Study Of Chelating Acid Fracturing In Ultra Tight Fractured Sandstone

The acid fracturing process of the tight sandstone reservoirs in Keshen area with high temperature and high pressure has poor injection property,and the acid-rock reaction rate is fast,the effective acid etched fracture length is limited.Conventional mud acid systems are prone to secondary precipitation,causing permanent damage to the reservoirs.Therefore,due to the good performance of the chelating acid,it was applied to the target area for acid pressuring stimulation and transformation.The chelating acid system with the characteristics of inhibiting secondary precipitation and slow reaction rate has significant advantages in acid pressuring of sandstone.However,as a new system,the conductivity of the etched fractures under the reservoir conditions and the turning rules of temporary plugging during acid pressuring are not clear,and it cannot guide the design and application of acid pressure in the field.In this paper,for the chelating acid system,the basic acid liquid properties,conductivity and temporary plugging turning rules in acid etched fractures were studied.First,the basic properties of the chelating acid system,such as dissolution rate and retardation performance,were tested.Then,conductivity of the acid-etching fractures was evaluated by the acid-fracture conductivity evaluation system to find the effects of the type of acid,acid-rock contact time,temperature,injection rate and closing pressure on the conductivity of acid etched fractures Afterwards,the advantages of chelating acid were further analyzed by analyzing the long-term conductivity of acid etched fractures and the alternating injection of multiple stages.The morphology of the fractures is described by 3D scanning system.Finally,the temporary plugging turning rules of the acid-etched fractures are tested by the temporary plugging experiment.The experimental results show that the chelating acid system has better corrosion inhibition performance than conventional earth acid,and the corrosion performance is outstanding;the conductivity of acid fracturing of chelating acid is more than 10% higher than conventional mud acid;Through comparative analysis,acid-rock contact time and reservoir temperature are the dominant factors affecting the conductivity;in addition,the long-term conductivity of the chelating acid is reduced by about 38%,which has a great advantage for extending the developing period.In the temporary plugging of acid-etched fractures,the pure fibers and the combination of fiber-particles can effectively plug the fractures at a 2mm width;a single type of temporary plugging agent cannot achieve effective plug the fractures at a 4mm width,and increasing the size or concentration of the particles in a certain concentration of fibers can significantly improve the temporary plugging effect.This study has certain guiding significance for the acid fracturing transformation of ultra-deep tight sandstone.