Feasibility Evaluation Of Fracturing And Acidizing Waste Liquid Re-injection After Treatment

Fracturing and acidizing operations have become the main technical measures for increasing oil and gas fields in China.The flowback fluid generated in fracturing and acidizing operations and the remaining working fluid after the completion of the operations are known as operation waste fluid.Operation waste liquid has the characteristics of complex composition,large amount of waste liquid,great difficulty in treatment and great harm to the environment.Reprocessing the stratum after treatment is a widely used method to save water resources.However,due to the high content of organic matter and high COD value in the treated operation waste liquid.When reinjection,the organic matter on the surface of the reservoir adsorbs,ion reaction,etc.,causing certain damage to the reservoir.It is of great significance to establish the feasibility evaluation program for the reinjection of fracturing backflow after treatment and put forward the sewage water quality index at the time of reinjection.In this paper,through the determination of scale formation,clay swelling property,and the influence of injection on the core permeability,the feasibility of the re-injection of the waste liquid after the treatment was evaluated,the evaluation procedure of the waste liquid re-injection after the treatment was established,and the suitable water quality index of the reinjection was put forward."Recommended indexes and analysis methods for water injection quality in clastic rock reservoirs"(SY/T 5329-2012)were used to analyze the water quality of the treated working waste liquid.By using clay swelling experiment and kerosene as contrast,the properties of clay swelling caused by waste liquid after treatment were evaluated.By measuring the scale formation amount and analyzing the scale type,the compatibility results of the treated waste liquid and formation water were obtained.The damage rate of different water quality(suspended matter content,oil content)to the reservoir was obtained by core displacement experiment,and the water quality index of the treated waste liquid was determined on the basis of the above experiment.The clay swelling experiment showed that the swelling rate of the treated working waste liquid was lower than 150% compared with the kerosene solution,and the reinjection of the treated working waste liquid into the reservoir would not cause excessive hydration and swelling of the clay.The compatibility experiment shows that when the mixing volume ratio of treated waste liquid and formation water is 9:1,the scaling amount is less than 20mg/L,and the compatibility is good.When the oil content and suspended matter content are less than 6.0 mg/L,the reservoir damage rate is less than 20% when the injection volume is 20 PV for the reservoir with a permeability of 8 mD or more.After treatment,acidified waste liquid has a high salinity and poor injection effect,so it needs to be mixed with water at a volume ratio of 9:1 for injection.Based on the above experimental results,combined with the current water quality standards for re-injection of oilfields,the recommended water quality indicators for re-injection of working waste liquids are as follows: oil content,suspended solids content is less than 6.0 mg/L,and mixed water scaling is less than 80 mg/L.The water injection clay expansion rate is less than 150%.The established procedure for the evaluation of the waste liquid re-injection of the operation is as follows:the analysis of the ion concentration of the waste liquid after the treatment ? the stability evaluation of the mixed waste liquid and the formation water after the treatment ? the effect of the water quality of the working waste water on the swelling rate of the clay ? Evaluation of the Influence of Wastewater quality on reservoir damage rate after treatment ? evaluation of damage rate of working wastewater to different permeability reservoirs after Treatment.