Study Of Clay Minerals Inhibition And The Thermal Stability Of The Clay Colloid

Clay minerals are the general name of fine dispersing layered hydrous silicates and amorphous hydrous silicate minerals. The main structure unit of clay minerals contains silicon-oxygen tetrahedron and aluminium-oxygen octahedron. The structure characteristics determine that clay minerals swell and disperse easily in aqueous solutions. This is an essential reason of formation damage caused by clay in the oil field development. Hydration and swelling of the clay minerals can be divided into two stages, namely surface hydration and osmotic swelling. The main factor of the surface hydration involves surface hydration energy of clay. The new combined water molecules seldom exceed four layers with thickness of probable 10 A. The osmotic swelling is that water molecules enter the layer intervals causing by osmotic pressure and layer spacing of clay become larger. The clay volume increased by osmotic swelling is larger than that caused by surface hydration. When the clay minerals swell to a certain extent, they will disperse to form finer particles, and migrate with the fluid flowing among the pores, causing the pore throat blocked. The main factors that influenc the clay particles swelling, dispersing and migration are mineral composition, exchangeable cations, dispersing degree and cohesion among the particles and so on. In the oil field development, because the mineralized degree of outside fluids is not compatible with the clay minerals of formation, it will cause hydration, swelling, and dispersing, and result in reducing formation permeability. This is called water sensitivity of the formation. The formation water sensitivity is related with clay mineral type, clay content, existing state, petrophysical proprety, outside fluid mineralized degree and cation composition and so on. Montmorillonite is the typical swelling clay minerals which usually consists of 2 silicon-oxygen tetrahedra and 1 aluminium-oxygen octahedron. The swelling, dispersing and migration of the clay minerals are related to the whole course in the oil field development, which have greatinfluence on the oil production. So it is actually meaningful to investigate the inhibition of clay minerals and develope clay inhibitors of excellent performance to improve oil production.The negative surface charge of montmorillonite comes from ion replacement. There are exchangeable cations among layers to keep balance of charge. Water molecules can adsorb on clay surface through hydrogen bonds and form hydration lsyers with exchangeable cations, causing montmorillonite to hydrate, swell and disperse. Karaboni studied hydration and swelling of montmorillonite with molecule dynamics, and found that swelling mechanism of montmorillonite is caused by two type of competition adsorption of water molecules. One is that water molecules enter hexagonal cavities of silicon-oxygen tetrahedron to form hydrogen bond with OH in the aluminium-oxygen octahedron. Another is that water molecules form hydrogen bond with oxygen atom in silicon-oxygen tetrahedron. This can explain traditional clay swelling inhibition mechanism of inhibitor K+, that K+ possesses ion radius equal to the size of hexagonal cavity in montmorillonite crystal lattice, it can penetrate into them and squeeze out the water molecules. At the same time, the hydration energy of K+ is the minimum among common cations (Na+,Mg2+, Ca2+,etc). K+ was the best inhibitor of clay minerals in history. NH4+ ion radius is slight larger than K+, it may penetrate into cavities in the course of vibration of oxygen atom in clay crystal. What's more, NH/ and K+ ion have the same low hydration energy. According to this consideration, we can sepeculate that NH4"1" has powerful inhibition effect on hydration, swelling and dispersing of montmorillonite. Urea is a type of acylamine compound with low molecular weight, the NH2 group may insert into hexagonal cavities of clay crystal, and generate inhibition properties. It was found that polyethylene glycol has powerful inhibition effect on clay mineral. When complxing with K+, they can make the rock harder in the course of soaking. In this thesis the inhibition effect of NH4+, K\urea, polyethylene glycol and their complexes on hydration, swelling and dispersing of montmorillonite were investigated with linear swelling and size distribution method. At the same time, the thermal stability of filtrate reducers and cooperative effect of polyethylene glycol and its complexes with other stabilizers were studied with chemical dynamics method.In contrast to K+, NH41" is characteristic of similar inhibition, and is capable of substitution for K+. This demonstrates that when the ion radius is equal to the size of hexagonal cavity in montmorillonite crystal lattice, it is not easy to be exchanged by other cations after embedding in the cavity, then on the one hand prevent water molecules from entering the cavity, on the other hand decrease the surface charge density, thus show inhibition of swelling, the inhibition mechanism is reasonable. The acylamino groups of urea also show inhibition ability. One of the NH2 group may insert into hexagonal cavities of clay crystal, and generate inhibition properties. The other NH2 group may adsorb onto clay surface by hydrogen bond. If there are excessive urea moleculars, the other NH2 group may be negatively charged and generate dispersing effect. So there is a maximum of inhibition ability of urea with increasing concentration.Adsorption of PEG on clay surface enhances the hydrophobicity and results in desorption of water moleculars, which induces inhibition of swelling. Linear swelling test is not suitable for characterization of inhibition ability of PEG. Shale recovery tests and size distribution experiments are used to characterize the macrosopic inhibition of PEG It's turned out that PEG alone are capable of behaving a certain inhibition effect on montmorillonite swelling. And the inhibition is stronger as the molecular weights of polyglycol become larger and as it becomes more hydrophobic. There are evident interactions between PEG and inorganic cations, and the interactions become stronger as the hydration energy of the cations decreasing.Complexing of PEG with K+ improved greatly inhibition for hydration of montmorillonite. At the same time, PEG enhanced the adsorption amount of K+, and inhibition effect of K+ increased. Adsorption of K+ induced single layer adsorption of PEG. The covering area of PEG on clay surface and the hydrophobicity increased. Thus both of the inhibition ability of K+ and PEG increased.There are also interactions between urea and NH41". Adsorption of urea enhanced the adsorption amount of NH41", which induced higher inhibition effect. Adsorption of NH4+ changed adsorption type of PEG, the hydrophobicity and inhibition ability of PEG were improved.It was found that the inhibition mechanisms of inorganic electrolytes and organic compounds (such as PEG and urea)were different. The effects of inorganic electrolytes can be explained with DLVO theory. Average particle size increased and size distribution become narrow with concentration increasing. The size distribution curve changed with addition of PEG or urea, which indicated the complexity of the inhibition mechanisms. Two peaks appeared on the size distribution curve when PEG was added in the solution alone. The average size of the first peak was smaller than the original particle size, and the average size of the second peak was larger than the original particle size. This indicates that PEG can stablize small particles and flocculate large particles. The peak of the large particles become larger as molecular weight of PEG increased. There are also two peaks on the size distribution curve when PEG and KCl were both added in the solution. But the average size of the two peaks were both larger than the original particle size. The peak of the large particles was larger as amount of PEG increased. Compexes of PEG and KCl were proposed to explain the inhibition mechanism. There are two peaks on the size distribution curve when urea was added in the solution alone. The average size of the two peaks were both smaller than the original particle size. The peak of the large particles becomelarger at first and then become smaller, which demonstrated the mechanism of both inhibition and dispersing. Introducing of hydrophobic unit of PO into PEG molecular result in great enhancement of hydrophobicity and inhibition ability of copolymers of EO and PO. The complex of the copolymer and K+ was more stable. There are interactions among NH4CI, KC1 and PEG Identical adsorption of urea and NH/ was the reason that urea showed more powerful inhibition ability. Complexes of urea/PEG/K+ and urea/PEG7NH4+ were the most powerful system to inhibit hydration, swelling and dispersing of montmorillonite.Thermostability of aqueous dispersions of clay minerals is one of the most important content in clay colloid chemistry. It is very important in the areas of industry, agriculture and environment protection. In aqueous dispersions of montmorillonite, the nature and interactions of clay particles, stablizers and water molecular are the main factor for stablization of the system. Among them the type, structure, nature and amount of the stabilizer show crucial effect. In this thesis, the thermostabiility of 6 stabilizers which are often used in drilling fluids is investigated with chemical kinetics method. It was found that instability of clay colloids which are stabilized with the 6 stabilizers was first order kinetic process. Kinetics constant, half-time, activation energy of instability process were obtained. The results accorded with industry applications. The rank of the thermostability is found to be as following: starch is the worst stabilizer, cellulose is better than starch, and NH4-PAN is the best stabilizer, which can stabilize clay colloid up to 210'C in 16 h. Thermostability and ti/2 show direct proportional relationship. Thermostability is larger with t\a- But there are no direct relationship between activity energy of instability and thermostability. As a whole, the activity energy is higher, the thermostability is better. It is found that PEG can improve remarkably the thermostability of clay colloid for the first time. At the same time, the thermostability of the stabilizers is evidently improved, which are...