Preparation And Properties Of Associative Drag Reducer For Shale Gas Fracturing

Hydraulic fracturing technology is the main treatment to enhance shale gas recovery and make commercial meet,further,drag reducer（DR）is a key point to slick-water fracturing fluids which could reduce flow resistance and energy consumption.High speed liquid in the pipe could induce polymer chain be broken and causes drag reduction rate of DR fall down obviously.Meanwhile,high salinity of flowback fluids is a big issue as well,so the high salinity of flowback fluids and the high speed in the pipe required that the drag reducer have to show excellent salt-tolerant and-shear resistance performance in field applications.In this thesis,a series of cationic monomers with various hydrophobic groups were designed.then by aqueous solution polymerization,a series of hydrophobically associative drag reducer were synthesized.The structure characterization,properties studies and performance evaluation were carried out,the mechanism of the structure affecting the salt resistance,shear resistance and resistance reduction were discussed.The work done in this thesis includes:1.Four kinds of allyldimethylalkyl quaternary ammonium salt monomers were synthesized,which with hydrophobic structure,marked as AQAS1,AQAS2,AQAS3 and AQAS4.The structures of the four hydrophobically modified monomers were characterized and confirmed by FTIR and ¹H NMR.2.Four kinds of hydrophobic associated polyacrylamide were synthesized by using four kinds of modified monomers with acrylamide（AM）,use water as a solvent.For P（AM/AQAS1）,the best solubility performance.And all of copolymers show good salt resistance,temperature resistance and shear resistance.Finally compare with P（AM/AQAS1）and HPAM drag reducing ability in 10000 mg/L brine water（Na Cl）,the result shows that P（AM/AQAS1）drag reduction rate can reach 60%at mass percentage of 1500mg/L,higher than drag reduction rate of HPAM about 10%.3.In order to further improve the solubility,acrylate was introduced to prepare four ternary hydrophobically associative acrylamide copolymers,named as P（AM/Na AA/AQAS1）,P（AM/Na AA/AQAS2）,P（AM/Na AA/AQAS3）,P（AM/Na AA/AQAS4）.The structures of four drag agents were characterized and confirmed by FTIR and ¹H NMR,and the effect of polymerization conditions on the apparent viscosity of the copolymer solution was investigated,and optimization conditions were obtained.4.The solubility,critical association concentration（CAC）,salt resistance,shear resistance and other properties of the copolymer reducers were investigated.P（AM/Na AA/AQAS1）,P（AM/Na AA/AQAS2）and P（AM/Na AA/AQAS3）were able to dissolve completely within 1 min,and P（AM/Na AA/AQAS4）took longer to dissolve,with the viscosity reaching stability after 37 min.P（AM/Na AA/AQAS2）,P（AM/Na AA/AQAS3）and P（AM/Na AA/AQAS4）had significant CAC,while P（AM/Na AA/AQAS1）did not show significant CAC.At 3000 mg/L,four copolymers showed salt resistance and shear resistance（viscosity retention above 85%）.And the copolymers are highly elastic and low viscosity fluids at high concentrations.Under the same conditions,the chain hydrophobic group can promote form a more tight network structure than the cyclic hydrophobic group.5.The drag reduce performance of DR were investigated,45 L·min^-1,the DR rate of four copolymers in fresh are between 73%-76%;When the brine is 20000 mg/L（Na Cl）,the DR rate of four copolymers are between 69%-72%;When the brine is 5000 mg/L（Ca Cl₂）,the DR rate of the four copolymers are between 56%and 61%.6.The reasons why the molecular structure affects the properties of copolymers were analyzed.While the hydrophobic groups are 9 carbon atoms,the sterically hindered of the cyclic group is larger,and it may tend to be more randomly distributed in the copolymer chain,that’s why the solubility of the cyclic group copolymer is better.While the hydrophobic groups are 20 carbon atoms,the branched group has a higher spatial site resistance and may tend to be more randomly distributed,so that branched group copolymer is more soluble than straight chain group copolymer.While the hydrophobic groups are also straight-chain groups,the solubility of the copolymer decreases as the carbon chain grows,and the small amount of long-chain groups introduced leads to a decrease in shear resistance.