Study On Residual Boron Crosslinker In Fracturing Backflow Fluid

The widely use of boron crosslinked HPG fracturing fluid in the oilfield resulted in a large number of fracturing flowback, for the purpose of emission reduction, resource utilization, fracturing flowback can be reused to formulate fracturing fluids after treatment. However, since the fracturing flowback contains a large amount of residual additives and high price of metal ions mixed by formation water, which are important factors influencing the reuse of fracturing flowback, and wherein the residual boron crosslinking agent is the key factor affecting the reuse. After adding basic additives in the treated water formulated guanidine gum base fluid, the base liquid is easy to be re-crosslinked automatically because of the alkaline environment, which made guanidine gum base fluid crosslinked in advance, resulting in obstruction and other issues with liquid pipelines. The presence of residual boron crosslinker directly impacts on whether flowback can be reused, therefore, researching for the residual boron crosslinker in fracturing flowback has great signification for achieving reuse fracturing flowback.Currently, there is no specific method for determining content of boron in flowback. Experiments in the thesis were screened the experimental conditions of extraction-ultraviolet spectrophotometry and azomethine-H acid spectrophotometry, and compared the precision, accuracy, etc. of extraction method, curcumin method and azomethine-H acid method. And the boron content in fracturing flowback was determined by these three methods, research showed that the most suitable method is azomethine-H acid spectrophotometry.For the residual boron crosslinker in fracturing flowback seriously impacted the reuse of flowback, the thesis carried out experimental research and application of stable complexation of boron and boron removal method.The results obtained by the complex method:the GLC, MTC and DPN were effectively stabled boric acids, their common feature is that their molecular structures containing the cis polyhydroxy. When the ratio of three ligands/boric acid is greater or equal to 2.5, the guanidine gum base fluid was not crosslinked. When the ratio of GLC/boric acid and MTC/boric acid are greater or equal to 2, DPN/boric acid is greater or equal to 2.5, the guanidine gum base fluid will not crosslinked even added lOmL of the 3wt% NaOH solution which the solution pH is 13. The GLC, MTC and DPN were used to formulate the gum linear and crosslinked gel in fracturing flowback water, the experimental results showed that three ligands can effectively leave the boron complex stabled, and the performance of temperature shear resistance were almost glue with the original liquid.The results obtained by the boron adsorption method:When the pH of boric acid solution was 6.0, the static adsorption got the maximum amount of adsorption units. The temperature had little effect on the adsorption units, so chose the room temperature as adsorption temperature. The adsorption isotherm showed that the adsorption process met the Langmuir adsorption model, it’s a single-molecule layer chemical adsorption. The adsorption rate curve showed that the adsorption process met the second order of Lagergren rate equation, indicating that rate-controlling step may be the complexation of the adsorbent complex with boron. Dynamic adsorption and desorption experiments showed that:the elution rate was 92.48%. The static adsorption method was not suitable for the removal of boron from the fracturing flowback, but dynamic adsorption method can effectively remove the boron from the fracturing flowback, and the gum linear and crosslinked gel formulated by the after-adsorption flowback had good properties.