Ping He,Lei Dai,,3,*,Xinyu Li,Zongjian Yang,Feiguo Hua,Liang Li,Bing Wei

1. College of Bioresources Chemical and Materials Engineering, National Demonstration Center for Experimental Light Chemistry Engineering Education, Shaanxi University of Science and Technology,Xi'an,Shaaxi Province,710021,China

2. Sinopec Northwest Oil Field Branch, Sinopec Group, Urumqi, Xinjiang Uygur Autonomous Region,830011,China

3. College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, Zhejiang Province,310027,China

4.Zhejiang Jinjiahao Green Nanomaterial Co.,Ltd.,Longyou,Zhejiang Province,324404,China

5. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University,Chengdu,Sichuan Province,610500,China

Abstract: Lignosulfonate, a byproduct of the pulp and paper industry, has been used in the oil-well drilling industry for a significant amount of time.Lignosulfonate and its derivatives serve different roles in the oil-well drilling industry because of their unique structures and properties. This review summarizes lignosulfonate and its derivatives, including lignosulfonate complexed with metal ions, lignosulfonate graft copolymers, lignosulfonatetannin complexes, and other lignosulfonate-containing composites, in terms of their preparation, properties, and potential applications in oil-well drilling industry. It provides readers with a quick review of existing studies in this area and some inspirations for future studies pertaining to the utilization of lignosulfonate-based materials in the oil-well drilling industry.

Keywords:lignosulfonate; oil-well drilling fluids; oil-well cementing

1 lntroduction

Lignin, a major component of most plants, is the second most abundant biopolymer on Earth[1]. Lignosulfonate (LS) is the sulfonated lignin, which is obtained as a byproduct of the sulfite pulping process[2]. LS can be isolated from spent pulping liquors through precipitation in alcohol and electrodialysis ultrafiltration[3-4]. It is typically prepared with various cations, including calcium[5-6],sodium[7],magnesium[8],and ammonium.LS possesses a hydrophobic aromatic structure, although it also contains hydrophilic sulfonate groups. Hence, it is an effective dispersant and a surfactant[4,6].In fact,LS was first used as a plasticizer or a water reducer in concrete in the 1930s[9], and it is also a good dispersing/setretarding agent in the concrete admixture industry[10].Moreover,it has been used in various areas owing to its high solubility as well as good stability, dispersibility,binding,and complexation properties[2].

LS was first used in oil-well drilling in 1949 to stabilize emulsions to control water loss in lime-treated muds, resulting in decreased torque on the drill stem,increased drilling rate, and improved borehole conditions[11]. It was later investigated extensively and used as a diluent/stabilizer/dispersant in oil-well drilling fluids (or drilling muds), oil-well cements, etc.,owing to its abundance, environmental-friendliness and cost-effectiveness. LS decreases the electrochemical attraction forces of clay, thereby decreasing the viscosity of drilling muds[12-14]. In addition, it provides drilling mud with sufficient viscosity to lift cuttings to the surface[4]. LS is suitable for improving drilling fluids because it stabilizes oil-in-water emulsions in emulsion-type drilling fluids[15]. Moreover, LS improves oil solubility in water and decreases the energy required to rotate the drill stem, thereby prolonging the life span of the drill bit[12,16-19]. The liquidity of cement slurry is important for oil-well cementing because the latter is associated with high temperature, salinity, pressure, and other harsh conditions. LS is an ideal retarder that extends the cement setting[20].

A lot of work has been done in the application of LS and its derivatives in the oil-well drilling industry;however,to the best of our knowledge,very few review papers have been published summarizing extant studies in this area. Therefore, we provide a thorough analysis of LS and its derivatives herein, including LS complexed with metal ions, LS graft copolymers, LStannin complexes, and other LS-containing composites,with respect to their preparation, properties, and application potential in the oil-well drilling industry.This review may provide readers with a quick understanding of extant studies regarding the utilization of LS and its derivatives in the oil-well drilling industry and ideas for further investigations.

2 LS and its derivatives

LS can be produced via different pathways; hence,different types of LS can be created. Furthermore, LS can be modified to obtain various derivatives. In this section, we discuss LS and its derivatives comprehensively in terms of their preparation,properties,and features.

2.1 LS with different metal ions

Various ion-based LSs, including sodium, chromium,calcium, and magnesium LS, can be generated via different production processes[21]. The properties of LSs are primarily affected by their complex cations.Shen et al[1]reported that the surface free energy of LS is dominated by sulfonation ions in their study comparing several LSs with different ions. The apparent viscosity of calcium lignosulfonate (CaLS) is generally higher than that of sodium lignosulfonate(NaLS) because calcium has a weaker electrokinetic repulsive force than sodium[22].

2.1.1 NaLS

NaLS, a direct byproduct of the papermaking industry,is a half-natural polymer material that exhibits reproducibility, biodegradability, and non-toxicity[23-24].NaLS is a well-known macromolecular surfactant with reasonable surface activity, rendering it capable of surface adsorption and particle dispersion. Qiu et al[25]investigated the aggregation behavior of NaLS, in which the critical aggregation concentration (CAC) of NaLS was determined to be 0.38 g/L. Consequently,they disclosed that NaLS appeared as individual molecules when its concentration was below the CAC,whereas it aggregated to form micelles when its concentration was above the CAC. NaLS can form films on substrates, enabling it to be used to prevent metal corrosion[10]; furthermore, it has been reported to form a compact film on the surface of coal to reduce the viscosity of the coal water slurry[26]. The properties of NaLS can be further improved via chemical/biological treatments. Chen et al[24]reported the hydroxymethylation of NaLS with formaldehyde,resulting in sodium hydroxymethyl lignosulfonate(NaHLS) with improved hydrophilicity. Furthermore,Zhou et al[7]reported the improvement in the physicochemical properties of NaLS with laccase modification. Specifically, the surface tension of NaLS in aqueous solution increased after laccase modification because of NaLS aggregation.

2.1.2 Chromium LS(CrLS)

NaLS can be complexed with chromium ions to improve its chemical nature and properties[27].Chromium ions have been reported to improve the hydration and temperature resistance of LS[28].Furthermore, more carboxyl groups (—COOH) are generated as a result of dichromate oxidation in the preparation of CrLS, thereby resulting in the improved bonding capacity of CrLS[27]. However, chromium ions cause severe pollution because they are heavy metal ions that exhibit metal toxicity and are difficult to degrade. Hence, CrLS with trivalent chromiumion and ferric CrLS have been proposed as substitutes for CrLS because of their lower toxicity[24,29]. Nonetheless, LSs with other metal ions are still in demand because of the development of environmentally friendly water-based LS products, owing to increasing attention on environmental protection[30].

2.1.3 CaLS

CaLS is another widely investigated LS. Ouyang et al[5]analyzed the physicochemical properties of CaLS and reported that the molecular weight of CaLS primarily affects its performance. For instance, CaLS demonstrated an improved adsorptive capacity on the surface of cement particles with its increased molecular weight. Moreover, its surface activity and foam production were improved as the molecular weight increased. The air-entraining effect of CaLS was also improved as its molecular weight increased, resulting in a decreased compressive strength of concrete[5].CaLS exhibits poor thermostability, and its weight loss in the temperature range of 200℃-400℃can reach 45% owing to bond degradation in the structure of LS[31]. CaLS has been reported to exhibit improved charge density and wetting capacity after a three-step modification comprising oxidation, sulfonation, and condensation[5]. Prasetyo et al[32]reported an improvement in the dispersibility of CaLS after treatment with a laccase-HBT (1-hydroxybenzotriazole)system.

2.1.4 Iron LS

Because NaLS is not thermostable, iron LS has been investigated[24,27]. However, the iron source (Fe2+or Fe3+) affects the properties of iron LS. Carrasco et al[33]investigated iron LS complexes via Fe Mössbauer spectroscopy in terms of the Fe-complexing capacity and chemical properties of the resultant products.Complex formation occurred at different coordination sites, and Fe3+showed better complexing capability with LS than Fe2+. Fe2+-LS is sensitive to oxidation in a system with pH value ≥7; hence, it is preferable to implement under slightly acidic conditions. Zhang et al[34]introduced Fe2+into LS via a two-step process,in which LS acid was first crosslinked with tannin extract followed by chelated Fe2+.The Fe2+-modified LS samples showed a higher adsorption amount of bentonite clay than the control without modification because the adsorption was realized via the bridging of chelated Fe2+between LS and bentonite. Khabarov et al[35]reported a galvanochemical method to synthesize iron LS, in which the as-prepared iron LS showed high biological activity.

2.1.5 Others

Poly aluminum chloride lignosulfonate (PALS) can be prepared from poly aluminum chloride and LS, and it exhibits good thermostability because of its low lignin content[36]. Titanium (Ti) and zirconium (Zr) LS have been reported as non-toxic and environmentally friendly additives for water-based drilling fluids[37-38].

2.2 LS graft copolymers

The exact structure of LS has not yet been confirmed,but it is generally deemed to have hydrophobic groups,including aromatic and aliphatic groups, as well as several hydrophilic groups (i.e., sulfonic, carboxyl, and phenolic hydroxyl groups), enabling it to be further modified through grafting polymerization[2]. LS has been grafted with acrylic acid, acrylamide, styrene,starch, etc. LS graft copolymers possess properties different from the LSs, allowing them to be used in more areas such as engineering plastics and soil/sand stabilizers[39-40].

2.2.1 LS-g-acrylic acid(AA)copolymer

The LS-g-AA copolymer can be fabricated using different initiation systems. Mai et al[39]reported the preparation of a LS-g-AA copolymer via a chemoenzymatic synthesis process, in which a phenoloxidase laccase was used. The molecular weight of the LS-g-AA copolymer was affected by the LS/AA monomer ratio.The copolymerization of CaLS and AA showed a significant reduction in the homopolymer proportion,whereas that of NaLS showed no such reduction.Ye et al[40]synthesized a LS-g-AA copolymer with CaLS and AA,in which Fenton agent was used as the co-initiator.Additionally, the LS-g-AA copolymer was prepared via the graft copolymerization of NaLS with acrylic monomers initiated merely by hydrogen peroxide because the presence of some reducing constituents in the crude LS served as a catalyst replacing ferrous ions[41]. PAA is used extensively for hydrogel preparation; hence, a composite hydrogel was prepared using LS-g-AA and hydroxyethyl cellulose[42]. The asprepared hydrogel exhibited good mechanical strength and stimuli-responsive swelling performance.

2.2.2 LS-g-acrylamide(AAm)copolymer

Abdollahi et al[43]reported the grafting of AAm onto LSs using the H2O2/CaCl2redox and potassium persulfate (KPS) thermal initiating systems,respectively. The AAm conversion and grafting percentage were dependent on both the initiator type and AAm concentration, whereas the grafting efficiency was affected only by the initiator type. He et al[44]proposed a LS-AAm-chitosan ternary graft copolymer that can be used as a water-soluble and pHindependent flocculant. Chang et al[45]fabricated a nano-lignosulfonate graft copolymer via the grafting of AAm and 2-acrylamido-2-methylpropanesulfonic acid(AMPS), in which KPS was adopted as the initiator.The resultant Nano-LS-g-PAM-PAMPS copolymer exhibited a thermal decomposition temperature beyond 295.16℃. Zhang et al[46]synthesized a LS-AAmdimethyldiallylammonium chloride copolymer and characterized its flocculation performance. The flocculation performance was attributed to electrical neutralization and the bridging effect.

2.2.3 Other LS graft copolymers

A LS-g-styrene copolymer was fabricated via the graft copolymerization of CaLS with styrene[47]. The monomer conversion was reported to be low when only peroxide was used as the initiator, whereas the monomer conversion increased significantly after the ozonation of LS, in addition to improved grafting efficiency and grafting degree. The graft copolymerization was dependent on factors including the dosage of peroxide and ozone, reaction temperature, and styrene-to-methanol ratio. The LS-gstarch graft copolymer was prepared using waxy maize starch and NaLS via laccase catalysis[48]. The resultant LS-g-starch graft copolymer showed effective antioxidant properties. Xia et al[49]reported a LSacrylonitrile(AN)copolymer fabricated with CaLS and AN. Specifically, CaLS was esterified via a reaction with acryloyl chloride to consume some hydroxyl groups and to introduce unsaturated double bonds.Subsequently, free radical copolymerization was implemented with esterified CaLS and AN. Liu et al[50]synthesized a LS-DMAA-KH570 copolymer via the grafting copolymerization of LSs, N,N-dimethylacrylamide, andγ-methacryloxypropyl trimethoxy silane (KH570). The resultant product exhibited good thermal stability.

2.3 LS-tannin complexes

Impelled by the search for alternative LS-based thinners for oil-well drilling, Zhang and Yin[51]prepared a Fe-LS-tannin complex via the crosslinking of LS acid and tannin, followed by chelation with Fe2+.The as-prepared Fe-LS-tannin complex exhibited favorable thinning performance and resistance in high temperature and salinity. Mohamad et al[52]proposed a tin-LS-tannin complex via a process similar to that reported by Zhang and Yin[51], in which chelation was performed using stannous ions. Ghazali et al[16]demonstrated that LS-tannin showed good thermal stability,and the residual weight of LS-tannin exceeded 60%when the temperature was increased to 500℃.

2.4 Other LS derivatives

Zhang et al[53]treated LS with nitric acid to introduce nitro groups into lignin and downsize the polymer chains. The resultant product (nitration-oxidation lignosulfonate, NOLS) was investigated as a drilling fluid additive in terms of rheology, filtration, and temperature resistance. Interestingly, NOLS benefited the growth of wheat seedlings, thereby proving their potential for use as a nitrogen fertilizer. Furthermore,the preparation of Azo LS via the coupling of a diazonium salt with LS has been reported[54].

3 Applications of LS and its derivatives in oil-well drilling

3.1 Drilling fluids(or drilling muds)

Oil-well drilling fluids are vital to oil field operations because they are used to cool and lubricate the drill bit,clean the hole bottom, transport cuttings to the surface,generate pressure control, etc. Drilling fluids are evaluated in terms of rheological properties, fluid loss prevention, and stability under different conditions[55].Aqueous drilling fluids comprising bentonite clay are used extensively in oil-well drilling operations, and a stable bentonite suspension is required[34]. In this context, LSs have been investigated comprehensively as an additive in oil-well drilling because of their versatile functional groups. In particular, hydroxyl and ether groups facilitate the adsorption of LS onto the clay surface via hydrogen bonding, whereas carboxyl and sulfonic groups enhance the colloidal stability, salt resistance, and thermal stability[52-53]. Hence, LS and its derivatives can be used in oil-well drilling fluids as thinning agents, thickening agents, clay stabilizers,fluid loss control agents,etc.

3.1.1 Thinning agent

Drilling fluids are supposed to exhibit sufficient viscosity to lift the cuttings. Nonetheless, their viscosity should not be excessively high to minimize friction pressure loss.Therefore,their viscosity must be controlled via the modulation of colloidal suspensions with additives. Bentonite is used extensively in drilling fluids to provide Bingham-type rheology to the fluids to lubricate the cuttings and transport them up to the surface[56]. Aqueous bentonite suspensions can easily coagulate/flocculate at high salinities and temperatures[57]. The stability of bentonite colloidal suspensions has been reported to improve when a steric barrier was applied[34]. Various LSs serving as thinning agents can be used in this context.

The metal ions in LS impart hydration and temperature resistance[53]. CrLS was the first LS used in oil-well drilling fluids[28]. The drilling fluid clay and CrLS are bonded by chromium ions, which provide thermal stability and adequate dispersibility at room and high temperatures. Furthermore, carboxyl groups are generated in the CrLS preparation as a result of dichromate oxidation, which improves the bonding between clay and CrLS[27].At room temperature, CrLS decreased the apparent viscosity of the clay from 50 to 36 mPa·s as the CrLS concentration (w/V) increased from 0.5% to 2.0%. In contrast, at high temperatures(50℃-130℃), the apparent viscosity of the clay decreased from 35 to 30 mPa·s as the CrLS concentration increased from 0.5% to 2.0%. However,the trivalent chromium in CrLS constituted 2 wt%-4 wt%, and the chromium ion causes severe pollution because it is a heavy metal ion that exhibits metal toxicity and is difficult to degrade. Consequently, the practical utilization of CrLS is prohibited[29]. LSs with other environmentally friendly metal ions have been produced owing to the development of water-based drilling fluids[30]. NaLS, a direct byproduct of the papermaking industry, satisfies the requirements of drilling fluid additives. Chen et al[24]reported the preparation of NaHLS via the hydroxymethylation of NaLS with formaldehyde and demonstrated that both NaHLS and NaLS decreased the viscosity of drilling muds at 180℃. In particular, NaHLS performed better than NaLS because of the increased number of hydroxyl groups on NaHLS, thereby enhancing its adsorption capacity toward clay particles. Furthermore,the performance of NaHLS was similar to that of ferric chromium lignin sulfonate, which implies that NaHLS can be used as a chromium-free drilling fluid additive.Zhang et al[34]reported the thinning capability of iron LS toward bentonite muds as a result of the bridging of chelated Fe2+between the bentonite surface and modified LS.

Chang et al[45]fabricated a LS graft copolymer via the grafting of AAm and AMPS and investigated the copolymer as an additive in drilling fluids.The drilling fluids containing the as-prepared LS-g-PAM-PAMPS copolymer exhibited shear-thinning behavior under static conditions. This LS-g-PAM-PAMPS copolymer exhibited good thermal stability, salt resistance, and calcium intrusion resistance in drilling fluids. Zhang and Yin[51]investigated the thinning performance of Fe-LS-tannin in aqueous bentonite mud in oilfields. The results showed that the Fe-LS-tannin functioned as a chrome-free modified LS with good resistance to elevated temperatures and matched tolerance to high salinity. Zhang et al[53]proved that the nitrationoxidation of LS improved its thinning performance because oxidation resulted in more carboxyl groups that improved the absorption of LS onto the surface of clay particles and improved the dispersion of clay particles.

3.1.2 Fluid loss control agent

The prevention of fluid loss is important to maintain the drilling fluid properties (such as density and rheology). Stable drilling fluids are necessitated for controlling drilling fluid loss via participation in filter cake formation[34]. Sharma et al[27]reported that fluid loss can be decreased from 16.0% to 9.0% at room temperature as the CrLS concentration is increased from 0.5% to 2.0%. Meanwhile, the temperature increase did not result in a significant increase in the fluid loss.These improvements can be explained by the strong bonding between CrLS and clay. The incorporation of 3.0 wt% LS-g-PAM-PAMPS copolymer was demonstrated to decrease the fluid loss to 7.5 mL after hot rolling under 200℃for 16 h[45].Liu et al[50]reported that the addition of only 3 wt% LSDMAA-KH570 copolymer significantly improved the fluid loss of bentonite-based drilling fluids. In detail,the fluid loss was only 6.2 mL before aging and increased to 9.8 mL after the fluid was maintained at 180℃ for 16 h. Moreover, the LS-DMAA-KH570 copolymer-containing drilling fluids exhibited good fluid loss control performance under the invasion of calcium salts.The fluid loss control performance of the LS-DMAA-KH570 copolymer can be attributed to (1)the decreased clay particle size as a result of the prevention of aggregation between clay particles owing to the incorporation of this copolymer and (2) the increased repulsive force between clay particles resulting from the adsorption of clay particles on this copolymer.

3.1.3 Thickening agent

LS and its derivatives are important thickening agents in oil-well drilling fluids. Abdollahi et al[43]reported that LS-g-AAm copolymers can improve the rheological properties of water fluids and control their fluid loss performance at low and high temperatures.NOLS has been demonstrated to increase the viscosity of bentonite-based drilling fluids at room temperature,owing to its high molecular weight[53].

3.1.4 Shale inhibitor

Gang et al[36]tested PALS as a shale inhibitor. They discovered that the clay-swelling ratio decreased from 69.5% to 47.5% when the PALS concentration increased from 0 to 0.3%. Furthermore, PALS demonstrated high inhibition property during montmorillonite hydrated expansion in mud ball immersion tests and the rheological evaluation of drilling fluids. PALS not only adjusted the particle size of montmorillonite significantly, but also effectively reduced the apparent viscosity of xanthan gum and PAM-based drilling fluids. Moreover, PALS reduces its viscosity at high temperatures,allowing it to be used as a viscosity reducer for deep drilling[36]. As shown in a study by Zhang et al[53],clay cakes exhibited a swelling rate of only 31.4%after immersion in a NOLS solution for 480 min, whereas the control in water exhibited a swelling rate of 70.6%. Furthermore, that study indicated that NOLS performed better than the original LS (a swelling rate 36.4% for clay cakes) in inhibiting clay swelling. This might be because the abundant hydroxyl and carboxyl groups of NOLS improved its adsorption on clay particles via hydrogen bonding,thereby preventing the cation exchange between the clay particles and medium, as well as preventing the penetration of water molecules.

3.1.5 Deflocculant

A deflocculant is required in drilling fluids to improve flocculated clay such that the rheological properties of the system at high temperatures can be maintained.Ghazali et al[16]investigated the potential of LS-tannin as a deflocculant in drilling fluids.The as-prepared LStannin demonstrated good thermal stability and performance in reducing the gelation of drilling fluids.

3.2 Oil-well cementing

Primary cementing is regarded as the most significant operation in drilling and well completion in the gas and oil industry because the quality of the cementing operations primarily affects the success of the subsequent drilling, completion, production, and workover efforts in the well[57]. Retarders, which are a class of typical additives in oil-well cementing, extend the cement setting and avoid premature hardening[20].LS and its derivatives are used extensively as oil-well cement retarders because they can adsorb onto hydrating mineral phases and retard hydration[20].Ouyang et al[5]utilized CaLS as a water reducer and demonstrated that the molecular weight of CaLS primarily affected their physicochemical properties in terms of the adsorptive capacity on the surface of cement particles, surface activity, and foam production.However, CaLS has been reported to exhibit poor thermostability. Bassioni and Ali[58]proved that the retardation of LSs was affected by counterions, in which NaLS was found to be 2 to 3 times more effective than CaLS in retarding cement hydration because the latter contained a higher amount of impurities (i.e., CO32-), thereby affecting the adsorption affinity. Zhou et al[7]modified NaLS with laccase and demonstrated that the modification improved the dispersion efficiency of NaLS in cement paste and enhanced the flowability of the cement paste.Furthermore, Azo LS has been reported to be a dispersant for oil-well cement that guaranteed low settime retardation[54].

4 Summary and outlook

The preparation, properties, and applications of lignosulfonate (LS) and its various derivatives in the oil-well drilling industry were reviewed. LS and its derivatives as sustainable and abundant materials have been investigated and used in oil-well drilling industry for more than half a century, and related investigations are still in progress. From our perspective, the following topics may be investigated in the future.

4.1 Environmentally friendly LS derivatives with high performance

The chromium lignosulfonate (CrLS) have been applied extensively in oil-well drilling industry due to its thermostability and dispersibility. However, its toxicity rendered it less applicable. Although some alternatives have been reported,they are still limited by a few shortcomings. Hence, more effort is required to develop high-performance and environmentally friendly LS derivatives.

4.2 Novel LS-based products for the oil-well drilling industry

More effort can be expended for developing a multifunctional LSs that may serve different purposes at different stages. Furthermore, lignin and LS have been investigated extensively for the development of various functional materials. For instance, watersoluble LS is a good candidate for hydrogel fabrication because of its abundant functional groups for crosslinking. In fact, hydrogels from synthetic polymers are commonly used in the oil-well drilling industry. Consequently, LS-based hydrogels may be investigated in the future and more LS-based products can be developed.

Acknowledgments

The authors acknowledge the financial support from the China Postdoctoral Science Foundation (2019M662 061), Postdoctoral Science Foundation of Zhejiang Province (zj2019135), National Natural Science Foundation of China (31901265), and Natural Science Foundation of Shaanxi Province(2019JQ-784).