Molecular Design Of Aqueous Two-Phase Associating Polyacrylamide And Continuously-mixed Process For Fracturing Fluid

Unconventional energy has become the focus of attention at home and abroad,volume fracturing is an effective means of unconventional energy exploitation,the technology in single horizontal well requires nearly ten thousand m³ fracturing fluid.The present fracturing fluid for volume fracturing mainly select slick water,linear gel and sand-laden fluid to produce map cracking.The slick water mainly contain the system of polymer and guar gum aqueous solution with a lower viscosity to communication microcrack.The linear gel stage mainly rely on guar gum solution to extended branch crack.The sand-laden fluid is made up of crosslinking guar gum with high viscosity,it plays role in filling main crack.Through the intercross and connection of microcrack,branch crack and main crack,the complex network is formed.Different fracturing liquids were needed to be used in different stages,and different mixing technique and storage methods were needed for different fracturing,therefore,it is difficult to select fracturing liquid and recovery process.Diversity of fracturing fluids caused to complex post-processing techniques and high processing cost for fracturing flow-back fluid.Considering the process characteristics of volume fracturing and technology requirement of fracturing fluid,a single agent is used to realize the various functions of slick water,linear gels and sand-laden fluid.The techonology solve the complicated problems of solution construction and simplifies recovery process of flow-back fluid.The study aimed to develop a single agent,it contain a variety of functions,as a slick water in lower concentration,linear gels in medium concentration,sand-laden fluid in high concentration.And the fracturing fluid system has advantages such as continuous construction and easy recovery,the properties and application in tigh reservoir were analyzed.Based on the mechanism of the turbulent boundary layer and the self-assembly theory of macromolecules,combined with the problem of dissolution difficulty of the thickener on the field and the complicated construction process,the new fracturing fluid was developed,it has the following characteristics such as lower drag rate,lower harm and sand-laden,which offered strong technical support for promoting process technology of volume fracturing and deep exploitation of unconventional energy.?1?In this paper,through aqueous solution free radical polymerization,the hydrophobically associating polyacrylamide?OWPAM?is prepared by acryla-mide?AM?,2-acrylamido-2-methyl propane sulfonic acid?AMPS?,and long-aliphatic-chain hydrophobic monomer C₁₈DMAAC.The monomer content,dispersant concentration,reaction concentration and other synthetic conditions are detailedly discussed.According to the solution properties,the optimal reaction conditions are determined:m?AM?:m?AMPS?:m(C₁₈DMAAC)=10:2:0.24,w?I?/%=0.3%,temperature:40?,?NH₄?₂SO₄ concentration:25%,dispersant concentration:8.0%.The structure of polymer OWPAM is characterizedbyinfraredspectroscopy?FI-IR?,Imagingmass spectrometry?H-NMR?and X-ray diffraction?XRD?.Thermogravimetric analysis?TGA?and light scattering instrument test results showed the polymer OWPAM and the emulsion have good stability.The critical association concentration?CAC?of polymer emulsion is 0.32%,which is determined by the apparent viscosity method.The emulsion particle size test and microscopic appearance description showed that the emulsion was well dispersed,the average particle size of the emulsion was 162.8 nm.through Fluorescence analysis,UV analysis,atomic force microscopy?AFM?and transmission electron microscopy?TEM?,it is found that the solution intermolecular association is more obvious when OWPAM concentration is higher than CAC.?2?The test results of OWPAM solution with low concentration showed that the viscosity of OWPAM solution is 8.0mPa.s at concentration of 0.1%,the surface tensions is 27.26 mN/m and the interfacial tension is 1.95 mN/m,which can meet the standard requirement of slick water.The viscosity of the system is about 5mPa.s in the environment of pH=6.0 and 9.0.When the mineralization degree was 40000mg/L,the viscosity of slick water decreased to 2.5 mPa.s.The fracturing fluid friction performance tester was designed and developed by reference to tube rheometer test theory.The equipment has high degree of automation,the friction characteristics can be tested with tubular inner diameter of 6 mm,9 mm,12 mm and 15 mm,the velocity of fluid is 2.0-12.0 m/s.Compared with moody chart,the equipment has high accuracy.The friction characteristics of OWPAM slick water has been tested with the friction performance tester.The test results showed that the drag reduction ratio can reach 73%at 25?atflow rate 10m/s with tubular inner diameter of 6 mm.The drag reduction rate of the OWPAM slick water decreased with the increasing temperature and salinity.The drag reduction rate is 65%at 60?andwith salinity of 40000mg/L.The corresponding clay stabilizer and flow-back improver is developed.Through temperature test,the layer drag reduction mechanism is verified,when the drag reduction rate was 73%,the temperature variable quantity of OWPAM slick water is half of that in water.?3?According to the rheology analysis of OWPAM solution with high concentration,kinds of additives were selected,and a OWPAM fracturing fluild system formed.The optimal fracturing fluild formulation are determined as follows:the concentration of OWPAM is 1.2 to 1.6%,clay stabilizer NWJ-1 is0.5-0.6%,the platoon aid CF–5D concentration is 0.4-0.5%,the stabilizer SAS60concentration was 0.3%,the fracturing fluild has good rheology properties.The final viscosity of the system is 58mPa.s after temperature and shearing resistance testing at 80?,and viscoelasticity test showed the storage modulus of system is2.4 Pa,the system has high elasticity.The static and dynamic sand carrying ability were tested and the maximum sand ratio can reach 40%,the system has good sand carrying ability.With intermolecular association increasing,the storage modulus and sand carrying ability of the system are improved.The analysis of system filtration resistance and filtration coefficient showed that the filtration coefficient of the system is 3.2 m/min^1/2,when ammonium sulfate concentration was 0.05%,the system gel can completely easily break down and the SFT of system is 24.2 mN/m,IFT is 0.21 mN/m.Both SFT and IFT value are low.FracpoPT was used as a tool of fracturing software to simulate profile of fracture for different fracturing fluids,the results showed that the stimulated reservoir volume is OWPAM>VES>guar gum?GG?.?4?According to the characteristics of fracturing flow-back fluid,the recovery process is developed.The recovery process are oxidation,adjustable acidity-alkalinity,flocculation and sedimentation.The influence of different treatment process on COD value of the system was tested.The ammonium persulfate was chosen as the oxidant processing first,and pH value was adjusted to 4,PAC was flocculation,eventually after sedimentation,the clear liquid which can be used for fluid preparation again is obtained.The drag reduction rate of the slick water prepared from the treated clear liquid is 75%at flow rate of 10m/s.The sand-laden fluid was prepared from the treated fracturing liquid,and the apparent viscosity of sand-laden fluid reached 40 mPa.s after shearing for 60min at 80?,exhibiting an excellent rheological property,which can satisfy the requirement of the fracturing fluid.The fracturing flow-back fluid can be recovered easily.?5?The performance of OWPAM fracturing fluid can meet the construction requirements,the OWPAM fracturing fluid was successfully tested in four oil wells of ZHI DAN oil reservoir area in the Yanchang oilfield.In the field test of OWPAM fracturing fluid,the properties of the slick water of the four oil wells were tested and the drag reduction rate of field fracturing fluid is more than 65%,which can meet the pressure drop and augmented injection requirements.The rheological property of the sand-laden fluid prepared with OWPAM was tested,the results showed that the viscosity of system is greater than 46mPa.s in four Wells after shearing for 60min at 80?,the sand-laden fluid has better rheological property.The viscosity of fracturing fluid system can reach3mPa.s after gel breaking,showing the fracturing fluid has good gel breaking properties.In field construction process,the online continuously mixed slick water can satisfy the dissolution and drag reduction rate in slick water.Because the continuously mixed slick water can not be intensive dissolved,the"A+B channel"was designed to keep carrying fluid properties,the A channel was used to adopted continuous mixed fluid in lower concentration,the B channel was used to adopt continuous mixed fluid directly in residual concentrations,the A and B channel worked simultaneous and the stabilizer was adding dropwise to finish construction.After the analysis of yield and construction friction,the OWPAM fracturing fluid in the test wells has lower friction and good cuttings transportation effect under different displacement,and the output of test well increases by more than 30%.