Hydrophobization Molecular Designs, Associative Behaviors And Gel Performances Of Sulfo-Hydroxypropyl Guar GUM

It is difficult to exploit the oil due to the worse physical property of domestic oil reservoir and the smaller pore throat. So, it is strict to choose a favorable fracturing fluid. And now we need to further develop the guar gum fracturing fluid, because the existing guar gum fracturing fluids can’t meet our requirements.Hence, we introduced sulfonic group, hydrophobic group, thermo-sensitive group into guar gum (GG) molecules by molecule design, and sulfonic hydroxypropyl guar gum (SHG), fluorocarbon hydrophobic associating anionic guar gum (FAGG), and thermo-sensitive hydrophobic associating anionic guar gum (PAGG) were synthesized, respectively. The structure characterization and aqueous solution properties of SHG, FAGG, and PAGG were studied by FI-IR,1H-NMR,13C-NMR,19F-NMR, XRD, DSC, DTG, ubbelohde viscometer, rotational viscometer, remoter, AFM, DLS, FS, UV, and so on. Meanwhile, all the three kind of guar gum derivatives were evaluated as fracturing fluids.Firstly, the SHG was synthesized and its properties were researched.(1) Sodium 3-chloro-2-hydroxy propanesulfonate (CHP) was prepared by epichlorohydrin and sodium bisulfate. Then, SHG was prepared by CHP and GG.(2) The results of thermal properties and crystallinity suggested that GG and SHG have significant decalescence peak around 104℃ and 116℃ respectively. The phase state of SHG was more stable than that of GG. After sulfonic group was introduced into GG molecule, the degree of crystallinity of GG decreased significantly. Intermolecular and intramolecular dehydration of GG were impeded by spacelocation-obstruct effect of CHP, which made the thermostability of GG improved.(3) The higher the degree of substitution, the smaller the intrinsic viscosity, apparent viscosity, and the values of n and k. At the same time, the higher the degree of substitution, the worse the temperature and shear-resistant properties. On the contrary, the higher the degree of substitution, the better the salinity tolerant properties. Moreover, the GG and SHG solutions behaved as pseudoplastic fluids and the values of n were less than 1. The storage modulus (G’) and loss modulus (G") of GG were higher than that of SHG, increasing with frequency.(4) The modulus, the temperature and shear-resistant properties of SHG gel were inferior to GG gel, but salinity tolerance of SHG gel was better than GG gel. For example the VIB of GG is 17.59%, but the VIB of SHG-1, SHG-2, and SHG-3 were 22.65%,30.58%, and 36.73%, respectively. Residue content after gel-breaking of SHG gel is 1/2～1/3 of unmodified gel. The core damage ratio of SHG decreased from 31.58% (GG) to 12.80%(SHG-3), and decrease rate was 59.47%.Secondly, fluorocarbon hydrophobic associating anionic guar gum was prepared by introducing fluorocarbon hydrocarbon chains into SHG molecule, and its properties were reported.(1) Fluorocarbon surface active intermediates (FSM) was prepared by 2,2,3,4,4,4-hexafluorobutanol(FOH) and isophorone diisocyanate (IPDI), and fluorocarbon hydrophobic associating anion guar gum was prepared successfully by the reaction between FSM and SHG. The synthesis technology of FSM is simple as follows:the ratio of n(FOH) to n(IPDI) is 1.0 to 1.0, and the amount of T-12 is 0.03wt%. Also, the reaction temperature is 80℃ and the reaction time is 6h. The synthesis technology of FSM is as follows:m(SHG):m(FSM)=10:0.5, the amount of T-12 is 0.05wt%, the reaction temperature is 70℃, the reaction time is 6h.(2) The hydroxyl content of FAGG decreased due to the replacement of fluorocarbon hydrocarbon chains, which weakened the intermolecular hydrogen bonds, and the higher the degree of substitution, the greater the weakening degree. In addition, molecular structure became more complex and irregular degree increased after introducing fluorocarbon hydrocarbon chains, which made crystallinity became poor and glass temperature decreased.(3) The viscosity of FAGG solution could greatly increase by introducing fluorocarbon hydrocarbon chains, and the apparent viscosity of FAGG solution increased with the increase of their concentration, which shoulded a phenomenon of sudden increase. At the low concentration, the interaction between fluorocarbon hydrocarbon groups of FAGG was mainly intramolecular. At the high concentration, intermolecular interaction took dominant position. The higher substitution of hydrophobic monomer led to the network structure formed easily and viscosity increased quickly. Also, the higher substitution of hydrophobic monomer give the solution better the temperature-resistant properties, shear-resistant properties and salinity tolerant properties, to some extent.(4) The DLS and AFM experiments showed that FAGG solution had mass of aggregates whose dimension were basically bigger than filtration membranes(0.45μm). The sultilluminated FAGG molecules can re-form cross-linking structure, which reflected that FAGG had favorable hydrophobically associative properties.(5) The shape factor of aggregates existed a minimum value in FAGG and SDS system. However, CTAB could make FAGG solution appear phase separation phenomena, and solution recovered clarified state with continuous increasing concentration of CTAB. Before phase separation, the shape factor decreased with increasing concentration of CTAB. After phase separation, the shape factor increased with increasing concentration of CTAB, then remained a constant value.(6) From the values of I1/I3 and the 19F-NMR, it is found that SDS had an effect to strengthen and break up the hydrophobic domain. However, CTAB could form"ionic combinative hydrophobically groups" with FAGG anions, which made hydrophobic groups increased in the solution. The addition of SDS and CTAB had a shielding effect on fluorine atom, and the movement of fluorine atom was limited. The peak of 19F-NMR became widen and moved to the low field.(7) With the increase of FAGG concentration, the micellar aggregation numbers of SDS (N) appeared a minimum value. Nevertheless, the micellar aggregation numbers of CTAB continued to increase with the increase of FAGG concentration.(8) When FAGG gel was used as fracturing fluids, its temperature and shear-resistant properties and elasticity were better than that of SHG. Compared with SHG, although the viscosity of gel breaking liquid of FAGG gel had increased, the interfacial and surface tension of gel breaking liquid decreased sharply. Decomposition fragments of FAGG possess both an ionic and fluorocarbon hydrocarbon chains, leading to higher surface activity. This makes breaking liquid flow back easily, and has little damage to the core from 13.81%(SHG-2) to 7.33%(FAGG-3).The decrease rate reaches to 49.92%.Finally, polyethylene glycol stearic acid ester (PEGS) were introduced into SHG, which contains polyethylene glycol hydrophilic segments and eighteen alkyl hydrocarbon chain. Then thermo-sensitive hydrophobic associating anion guar gum (PAGG) was obtained.(1) Polyether reactive intermediates (PSM) was prepared by PEGS and IPDI, and PAGG was prepared successfully by the reaction between PSM and SHG. The synthesis technology of PSM is simple as follows:the ratio of n(PEGS) to n(IPDI) is 1.1 to 1.0, and the amount of T-12 is 0.03 wt%. Also the reaction temperature is 80℃ and the reaction time is 8h. The synthesis technology of PAGG is as follows:the amount of T-12 is 0.05wt%, the reaction temperature is 80℃, the reaction time is 6h.(2) The XRD showed that the longer polyethylene glycol segments made the worse the crystallinity of PAGG. The DSC suggested that glass transition temperature decreased with the increase of polyethylene glycol segments.(3) The higher the degree of substitution, the more the hydrophobic domains, and the changing law of the PAGG solution performance is roughly identical to FAGG in certain extent. The longer the polyethylene glycol segments, the weaker the associative performance of PAGG at room temperature. But at high temperature, the longer the polyethylene glycol segments, the stronger the associative performance of PAGG. Importantly, the PAGG possesses obvious thermosensitivity. It should benoted that the apparent viscosity of PAGG solution is slightly smaller than FAGG at low temperature, but bigger at high temperature.(4) When the PAGG was used as fracturing fluid, some favorable properties could be also achieved, although the expensive fluorocarbon chains were replaced by cheaper hydrocarbon. The elasticity of gel system had greatly improvement after introducing PAM into PAGG. The longer the polyethylene glycol segments, the greater the properties of PAGG gel. The viscosity of breaking liquid of PAGG gel was bigger than SHG. Interfacial and surface tension of breaking liquid of PAGG gel were slightly more than that of FAGG but much less than that of SHG. Consistently, core damage of breaking liquid of PAGG gel was slightly bigger than that of FAGG but much smaller than that of SHG.