| With the increase of the difficulty of oil and gas exploitation,fracturing technology becomes the key to increase production.The frequency of using of guar gum fracturing fluid is also increased because of the demand for increasing production and the improvement of frac technology.Guar gum fracturing fluid is the one of water-based fracturing fluid,and then many environmental problems also have emerged,which are not only in water resources but also in how to treat the flowback water.From the point of view of environmental protection,this paper summarizes and analyzes the guar gum fracturing fluid system and the components of its flowback of water,and the flowback water recycling fracturing fluid is proposed.According to the analysis of the microscopic morphology by scanning electron microscopy,it was found that during the preparation of the fracturing fluid,the guar gum involved in the morphological changes was a filamentous or ribbon-like morphology in which the guar gum molecules aggregated.Therefore,the optimization of guar gum concentrates on the rapid dispersion and shortening of ribbon-like appearance time.According to the main influencing factors of recycling flowback water of guar gum fracturing and the mechanism of guar gum microscopic morphology,a scheme of sulfonation modified guar gum?SGG?was proposed,and sodium lignosulfonate was added to improve its dispersibility.The basic scheme of SGG synthesis was to use wet method to mix 50 g of guar gum with 80 mL ethanol and isopropanol?1:1 volume ratio?at 60-80°C under the conditions of sodium hydroxide catalysis.The droplet of aqueous solution of sodium2-chloroethylsulfonatewas added,whilethe n?NaOH?:n?sodium2-chloroethanesulfonate?was1.5:1,and after 3-5 h,0.01%sodium lignosulfonate was added for compounding.Washed the production to get the ISG?instant disperse guar gum?.The ISG had better dissolution and its viscosity increased quickly in water and could reach 80%of the maximum viscosity within 1.5 minutes.Based on IR,XRD,TG,DSC and other testing methods,it was confirmed that the product was synthesized.The guar fracturing fluid needed to be evenly added with cross-linker to form a stable fluid and bind the water molecules during the cross-linking.When the gel was broken,it was necessary to evenly add the breakers to break the guar gum ribbon,released the water molecules quickly,reducing the viscosity and breaking the gel.And the high temperature delayed organic boron crosslinker,BN-2 and BN-4,was synthesized.The basic synthesis scheme was to mix sodium gluconate,sodium hydroxide,boric acid?or borax?and water at 80-90?,and react 2-4 h.Through the simulation of the residence time of fluid in the reservoir,found during the construction stages of fracturing fluid had the differences in reservoir temperature tolerance,and testthe rheological properties of the fracturing fluid after breaker was simulated by the laboratory simulated formation temperature.The rheological properties of the fracturing fluid after breaker were simulated by the laboratory simulated formation temperature.According to the reservoir conditions in the Ordos Basin,the composition of flowback water was analyzed,the main factors influencing the recycling fracturing fluid were the residual boron ions,peroxides and other ions in the flowback water.The influence of the ions concentration of ISG fracturing fluid performance by adding ions in different concentrations to deionized water,determined a reasonable range of water with the ion concentration was Ca2+concentration less than 60 mg/L,the concentration of Mg2+was less than 120 mg/L,Fe2+,3+concentration was less than 8 mg/L,peroxide concentration was less than BO33-less than 10 mg/L.5 mg/L,the degree of mineralization should be less than30000 mg/L,and the other ions concentration were able to be as low as possible.According to this requirement,the flowback water treated by oxidation of gel breaking and slurry separation,coagulation sedimentation,membrane filtration process,and the removal of COD and SS was a 94%and 93%,the viscosity decreased to 1.3-1.6 mPa·s.The chromaticity was 5.6-14.6 times,and the pollutants were controlled in a reasonable range.Then got the treatment water.The temperature stabilizer TS-2 and ligand agent LA-2 were added into the treatment water to improve the performance of the recycling fracturing fluid so that could fit the requirements.Through lab experiments,the general formulation of ISG fracturing fluid system was including 0.36%ISG,0.6-1.0%crosslinking ratio of organic boron crosslinker BN-2 or BN-4,0.2%drainage agent,0.1%anti swelling agent,0.03%CB-3 and 0.02%ammonium persulfate.The interfacial tension of the gel breaking liquid was 32.25 mN/m,1.22 mN/m,the residue content was 288 mg/L,and the anti swelling property was 66.8%.LA-2 and TS-2 needed to be added to the treated water when recycling to prepare fracturing fluid.The viscosity of the breaking liquid was 33.18 mN/m,1.19 mN/m,the residue content was 306 mg/L,and the anti swelling property was 67.3%.On-site application:The basic sequence of on-site application was on-site clean water quality analysis,laboratory testing on fracturing fluid performances,chemical material on-site checked,and fracturing operations.The ISG fracturing fluid system had been successfully applied to the B-layer of the 0XX-D02 gas well.The fracture pressure of the well was 32.55MPa,and the construction pressure was 50.17-46.61 MPa,while the pumping ratio was 4.0-4.2 m3/min.The liquid used 370.5 m3 and the proppant used 37.8m3.The flowback rate was 41%and the daily gas production was 1.15*106 m3.Good application results had been achieved.After the flowback water of ISG fluid was collected in the field,treated it to get the treatment water.In order to ensure that the treatment water and the fracturing fluid could successfully complete the frac pumping,the four schemes of the treatment water to the on-site clean water was 1:2?volume ratio?,1:1?volume ratio?,2:1?volume ratio?and without on-site clean water were applied one by one.After used 110m3,122 m3,238 m3,80 m3 treatment water in turn,during fraced Yan 3XX-D08,Yan 5XX-D01,Yan 5XX-D06 and Yan 0XX-DXX wells,achieved the better results.The 3XX-D08 well was fraced three stages to B,S and H layer,and the fracturing fluid was pumped 1363.6 m3 and the proppant was pumped 92 m3.The average sand ratio was 21%and the flowback rate was 40.1%.And its daily production gas was 1.48*106 m3 at end.The treatment water was used 110 m3during pumping PAD?prepad fluid?and slurry?7%sand concentration?steps.Yan 5XX-D01 well has four fracturing stages for BX,S and H layers,1269.7 m3 fracturing fluid injected,and 149.2m3 proppant pumped,with a 57.5%return rate and a daily production capacity of 1.02*106 m3 per day.The accumulative used of treatment water at the well was 122 m3.The treatment water was used in the PAD and slurry?14%sand concentration?steps.The well 5XX-D05 fraced four stages to BX,S and H layers,and 1361.8 m3fracturing fluid injected,and the proppant accumulative amount was 136 m3.The flowback rate was 47.35%,and the daily production gas was 4.1*105 m3 per day.The accumulative use of treatment water was 238 m3 in the PAD,slurry?28%sand concentration?and flush steps.Yan 0XX-DXX well has one stage for B-layer,302.4 m3 fluid injected,and33.5 m3 proppant pumped.The average sand ratio was 24%,the flowback ratio was 43%,and the daily production gas was 1.86*106 m3 per day.The treatment water was used 80m3 during the PAD,slurry?25%sand concentration?and flush steps.The treatment water of YAN 3XX-D08,YAN 5XX-D01,YAN 5XX-D06and YAN 0XX-DXX was treated with ultrafiltration membrane,and the maximum amount of treatment water collected was 220 m3 per day.The treatment water used at Yan 0XX-DXX well was treated by reverse osmosis membrane process,and the daily output was only 40 m3.The ultrafiltration process has high efficiency,and the loss of the reverse osmosis membrane was much higher.Therefore,it wass recommended to use the reconstitution solution diluted with treatment water and clean water?2:1 volume ratio?on site for large-scale application. |
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