The Key Technologies Of Plug Removal And Injection Stimulation In Injection Wells Of Shanshan Oilfield Fractured Reservoir

Shanshan oilfield is taken as the research object in this paper. The main reasons of low injection rate are analyzed; The damage mechanism and damage range of injection well are determined; A selection model of wells and layers in injection well acidizing and an acidizing model of fractured reservoir are established; An efficient acid system is proposed. Eventually, a set of efficient injection stimulation technology is come into being. Specific work is as follows:(1) By systematically analyzing the reasons of the high injection pressure and low injection rate in injection wells, it is proposed that the geological structure, connectivity, reservoir properties, drilling and completion damage and the change of injection condition are the main reasons that lead to high injection pressure in the early injection stage. While the injecting water’s quality, clay damage and the damage caused by stimulation or other factors lead to the increasing pressure after injection;(2) Using the fuzzy matter element evaluation method and by considering permeability, the effective porosity, skin factor, layer’s thickness, connectivity, real injection coefficient and injectivity index reduction, a model to select acidizing layers specially for injection wells is set up. Besides, the connectivity and injectivity index reduction haven’t yet been considered in the previous similar models. By calculating ten injection wells in Shanshan oilfield as an example, this model is verified valid and the conclusion is consistent with the actual situation, which can provide the theoretical basis for acidizing optimization;(3) The reaction mechanism of hydrochloric acid, hydrofluoric acid and sandstone mineral is studied by numerous experiments. Aimed at effectively improving the plug removal effect and reducing the acidification secondary damage, a new acid system--FTC acid system for sandstone acidizing is proposed. The acidity characteristics test, dissolution test, corrosion inhibition evaluation test, displacement test and microscopic pore structure evaluation test show that the acid has good retarder, corrosion inhibition and anti-scaling characteristics, which is an excellent acid system with low damage and deep penetrating.(4) Based on the empirical parameters, which can reflect the actual situation of the formation water and the formation, particulate trap mechanism, and classical percolation model (convection equation), the damage degree and radius after injection in the oilfield is simulated combined with the experimental data of cores. The model is solved by semi-analytical approach.(5) By obtaining reservoir fracture distribution data, equivalent discrete fracture networks and permeability tensor, the fractured tight sandstone reservoir is transferred into homogeneous anisotropic reservoir. Then acidizing simulation in natural network fracture reservoir is realized based on the mature model of two acids and three minerals.(6) In order to achieve the acid distribution and facilitate the safe and effective implementation, the foam diversion and chemical particles diversion acidizing technology is proposed. And the diverting agent with good shunt effect, no damage to stratum and on-site implementation is developed.(7) According to the reservoir parameters, laboratory test results and the simulation result, the determination method of practical construction parameter and the general scope are provided. The research findings have guided field acidizing treatments four times, which achieves a good acidizing effect and with the successful rate of100%.In this paper, the series of research results provide theoretical basis and technical support for plug removal and injection stimulation in injection well of Shanshan oilfield. Furthermore, it provides certain theoretical basis and research approaches on acidizing technology in injection wells, which enriches and improves the related acidizing simulation study in the fractured sandstone reservoir. Also, the deficiencies of the current research on the theory and technology of injection well acidizing at home and abroad are made up.