| Oil-based drilling fluid can completely inhibit clay minerals hydration in the formation,which has many advantages such as good borehole stability,stable the performance of drilling fluid and protect the oil reservoir that be widely applied.But there exist serious problems such as environmental pollution and high cost.Therefore,it is a trend of the development of water-based drilling fluid technology that has similar to oil-based drilling fluid performance to replace the oil-based drilling fluid,especially shale gas development.The shale formation has high clay mineral content,longer horizontal section of the shale gas horizontal well,which results in the contact time of drilling fluid and formation increases,the shale hydration become more serious and borehole instability become more prominent.In order to realize this substitution,water-based drilling fluid can completely inhibit the osmotic hydration and surface hydration of the clay minerals like oil-based drilling fluid.At present,the theory and technology of water-based drilling fluid can only effectively inhibit the osmotic hydration of clay minerals and can't effectively inhibit the surface hydration of clay minerals.Therefore,the theories and methods of inhibit surface hydration of clay minerals is urgently needed built.Then that can guide to build new water-based drilling fluid system that similar to inhibition performance of oil-based drilling fluid,without a(small)harm to the environment and low cost,which replace oil-based drilling fluid.At present,there almost no quantitative research of hydration degree and hydration state at home and abroad,no corresponding research methods and no theory and evaluation method of inhibiting clay minerals surface hydration.So this paper is almost from scratch.The following innovations through a series of studies have been achieved.This paper establish evaluation method of hydration degree and surface hydration of clay minerals.The comprehensive evaluation method includes through isothermal adsorption method of clay minerals under different relative humidity in the moisture to measure absorbed water(constraint water)content of clay minerals under different conditions.Through X-ray diffraction method to measure the basal spacing(d001,of clay minerals under different conditions and through thermo-gravimetric analysis to measure adsorbed water content and type of clay minerals.The types and content of clay minerals bound water(including free water,capillary condensation water,osmotic hydration water,surface hydration water)can be evaluated through comprehensive analysis experimental data of this three methods,which can analyze and evaluate whether the clay minerals samples have surface hydration,hydration degree(the adsorption water content of clay mineral surface)and the permutations layer number of adsorbent water molecules(adsorption state).The action principle of intercalation adsorption inhibit surface hydration of clay minerals was put forward,and the evaluation method of inhibition performance was established,and the correctness and feasibility of this principle were verified.The action principle of intercalation adsorption inhibit surface hydration of clay minerals is that the adsorption group of intercalator with an arrangement of single tile intercalate into the interlayer space of clay minerals by absorbing,intercalating,ion exchange,and so on.The adsorption group replace exchangeable cations in the upper and lower surfaces of crystalline layer of clay mineral,preference to occupy negative charge position(active site)of silicon tetrahedron,block the adsorption of water molecules or replace water molecules adsorbed,taut adjacent crystal layer of clay minerals,minimize basal spacing of clay minerals,expel the interlayer water through synergy of adsorption group and hydrophobic chain,and thus inhibiting surface hydration of clay mineral.This chemical agent is known as "intercalation adsorption clay minerals surface hydration inhibitor",intercalation inhibitor for short.Through its role can be realized that the clay minerals does not occur surface hydration when dry clay minerals without hydration is added into water with this inhibitor or clay minerals with surface hydration occur surface dehydration when added this inhibitor,which can achieve the effect that totally inhibit surface hydration of clay minerals similar to oil-based drilling fluid.Based on this principle,screening and synthesizing a batch of intercalator model compounds.Through clay minerals samples intercalated before and after proceed isothermal adsorption method,X-ray diffraction method,thermo-gravimetric analysis method to systemative research the effect of this kind of intercalator on the surface hydration of clay minerals.The results show and verify that the functional groups of intercalator has a strong adsorption effect on the upper and lower layers of the two adjacent silicate crystals in the clay minerals and form stable intercalation compound that can't destroy by heating or washing with other polar molecules.And clay minerals in the oil and aqueous solution with such inhibitors can both completely inhibit the surface hydration of clay minerals.After adding a certain amount of this inhibitor,the inhibitor can make complete hydrated clay minerals occur dehydration,which proves the validity and feasibility of "the action principle of intercalation adsorption inhibit surface hydration of clay minerals".The relationship of the intercalation adsorption effect of various intercalator and their effect on inhibiting surface hydration of clay minerals is studied.The results show that amine compounds as intercalation inhibitors intercalate interlayer spacing of clay minerals,form a flat of single molecule adsorbed layer,make the basal spacing of sodium montmorillonite is less than 1.4 nm,which can achieve the purpose of effectively inhibit clay minerals surface hydration at the same time.The intercalation adsorption action of alkylamine and their molecular structure relationship is put forward,and the molecular structure design principle of the intercalation inhibitor is presented.Intercalator should have good water solubility and hydrophobicity,selecting the primary amine group as the adsorption group and hydrating group and the carbon chain skeleton as the hydrophobic chain by experiment.It is found that the length of hydrophobic chain and the number of primary amine groups of alkylamine have an important influence on the saturation adsorption and adsorption rate constant of alkylamine adsorbed on clay minerals.The saturated adsorption content of alkylamine adsorbed on sodium montmorillonite decreased and the adsorption rate constant increased with the increasing of the length of hydrophobic chain.The length of hydrophobic chain has a very important effect on the arrangement of alkylamine in the interlayer space of clay minerals.As the length of hydrophobic chain increase,the intercalation arrangement of alkylamine in the interlayer space of sodium montmorillonite change from slant single to single tile,then to slanted single.According to the action principle of intercalating adsorption inhibiting surface hydration of clay minerals,the single tile is the best arrangement of intercalators in the interlayer space of clay mineral that the length of hydrophobic chain is 4-7 equivalent carbon atom.The saturated adsorption content of alkylamine adsorbed on sodium montmorillonite decreased greatly and the adsorption rate constant increased dramatically with the increasing of the number of primary amine groups.The saturated adsorption content of alkylamine adsorbed on sodium montmorillonite and the adsorption rate constant decreased slightly with the increasing of temperature.The basal spacing of alkyldiamine intercalate into sodium montmorillonite in the wet state is 1.32 nm.Combined with the experimental results of intercalating inhibit surface hydration of sodium montmorillonite,alkyldiamine could inhibit surface hydration of sodium montmorillonite,but still exist one layer water molecule.The basal spacing of branched polyethyleneimine(BPEI)with multiple primary amine groups intercalate into sodium montmorillonite in the wet state is 1.39 nm,and BPEI can completely inhibit surface hydration of sodium montmorillonite.Therefore,the more the number of primary amine groups of intercalation inhibitors,the better,at least two.According to the molecular structure design principle of intercalators,BEN-5NH2 is synthesized in the room.The intercalating inhibitive performance of BEN-5NH2 is evaluated by the evaluation method of intercalating inhibit surface hydration of clay minerals.The research results show that BEN-5NH2 can inhibit completely surface hydration of sodium montmorillonite.The intercalating inhibitive performance is considerably larger than hexamethylenediamine,but slightly be less than BPEI,which further verify the action principle of intercalation adsorption inhibit surface hydration of clay minerals and molecular structure design principle of the intercalation inhibitor.An effective" intercalation adsorption clay minerals surface hydration inhibitor" is developed in the laboratory. |
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