Study On The Synthesis And Performance Of Scale-inhibiting And Dispersing Water Treatment Agent For Oilfield

In recent years,with the rapid development of the global economy,the demand of world for oil continues to increase,and oil is still an important energy source that people can develop and utilize.However,the problem of oilfield scaling has greatly affected the oil extraction process.Scale inhibitor for oilfield is a chemical reagent that can effectively inhibit oilfield scaling.From the past to the present,many researches on scale inhibitors have been carried out.With the increase in environmental protection requirements,the demand for green scale inhibitors is also increasing.Therefore,the research and synthesis of novel and environmentally friendly scale inhibitors has become a hot spot for future research.Because polyaspartic acid(PASP)possesses phosphorus-free,non-toxic and good biodegradability.PASP-based inhibitors are the most promising alternative to conventional scale inhibitors.However,the oilfield water environment is more complicated,it is necessary to modify the PASP to inhibit scale in the high-temperature and high-salt water environment.Some work emphasized that the introduction of sulfonic acid groups(-SO₃H)into the molecular structure can optimize the comprehensive scale inhibition performance of the scale inhibitor.Therefore,a modified PASP containing-SO₃H(PASP/ASA)was designed and synthesized in this paper,and it was found that the overall performance of PASP was improved while maintaining the original green chemical structure of PASP.However,this PASP derivative is rarely applied in the field of oilfield scale inhibition currently.In this paper,the structure of PASP/ASA was characterized by Fourier Infrared(FT-IR)and ¹H-NMR.Thermogravimetric(TG)analysis showed that PASP/ASA has good heat resistance.The scale inhibition performance of PASP/ASA was evaluated by static scale inhibition method.Among them,when the dosage of PASP/ASA is 2.5 mg?L^-1,the maximum calcium sulfate(Ca SO₄)scale inhibition efficiency can reach 100%;when the dosage is 10 mg?L^-1,the maximum calcium carbonate(Ca CO₃)scale efficiency can reach 83.36%;in the simulated oilfield water environment,when the dosage is 30 mg?L^-1,the average comprehensive scale inhibition efficiency can reach 61.63%.Compared with PASP,the scale inhibition effect of PASP/ASA has been improved to a certain extent.Compared with the commercial scale inhibitors,PASP/ASA has stronger Ca SO₄scale inhibition performance and slightly weaker Ca CO₃scale inhibition performance.In general,PASP/ASA has better temperature resistance and salt resistance.Scanning electron microscope(SEM)and X-ray diffractometer(XRD)were also used to observe and study the changes in the morphology,crystal form and structure of scale crystals before and after adding PASP/ASA.Through the experimental results of SEM and XRD,it can be inferred that the addition of PASP/ASA inhibits the normal growth of scale crystals,and changes the crystal form of scale to a certain extent.Finally,the crystal structure of scale is gradually loose and difficult to accumulate.In addition,since carbon dots(CDs)were first discovered,due to their excellent optical properties,good water solubility,low toxicity and biocompatibility,environmental friendliness and low cost and many other advantages,they have been received extensive attention in many fields.CDs are composed by a carbon core and surface groups these two parts.The surface and edges of CDs are generally bonded with a large number of oxygen-containing functional groups(such as carboxyl(-COOH),hydroxyl(-OH)and ether groups(-O-)).It happens that these oxygen-containing functional groups are the main functional groups that inhibit scaling.Therefore,the CDs with abundant oxygen-containing functional groups on the surface was synthesized,which not only maintains the advantages of CDs materials,but also occupies the scale inhibition properties of these functional groups.In this article,fruit pomelo peel,cheap and easily available citric acid(CA)and allyloxy polyethoxy ether(APEG)were recycled as raw materials to synthesize a new type of low-cost green oilfield carbon quantum dot scale inhibitors(PCA-CDs)by hydrothermal method.Transmission electron microscope(TEM),XRD,ultraviolet-visible spectrophotometer(UV-Vis),fluorescence spectrometer,FT-IR and X-ray photoelectron spectroscopy(XPS)were used to basically analyze and characterize the prepared PCA-CDs.Most importantly,PCA-CDs was also used for the first time to explore its Ca SO₄,Ca CO₃and barium sulfate(Ba SO₄)scale inhibition performance.The static scale inhibition method was used to explore the scale inhibition performance of PCA-CDs obtained under the condition that the optimal hydrothermal synthesis time is 8 h.When the dosages of PCA-CDs were 55 mg·L^-1and 113 mg·L^-1,the maximum scale inhibition efficiencies against Ca SO₄and Ca CO₃could reach 97%and 95%,respectively.When the dosage of PCA-CDs is in the range of 22 mg·L^-1?27 mg·L^-1,its Ba SO₄scale inhibition efficiency is about 89%.SEM and XRD were also used to explore the changes in the morphology,crystal form and structure of scale crystals before and after adding PCA-CDs.From the experimental results,it can be inferred that PCA-CDs can chelate scale-forming metal ions in the solution and can be doped on the growth active sites of scale crystals.PCA-CDs can also hinder and delay the normal growth of scale crystals,thereby destroying the dense structure of scale crystals.