Materials Science Forum Vol. 847

Abstract: It is difficult for conventional drilling fluid filter cake to form integration cementation with cement sheath, which causing weak cementation of the second interface. Therefore the following researches on improving the second interface cementation strength were carried out based on alkali activation mechanism of metakaolin. Cementation strength between metakaolin drilling fluid filter cake and cement sheath has been observed; the mechanism has been analyzed through SEM, XRD and FT-IR; engineering application performance of metakaolin drilling fluid has been studied; and circulation time of the technology has been researched. The results of the experiments showed that: 1) adding metakaolin into drilling fluid was helpful to improve the second interface cementing performance; 2) calcium hydroxide produced by cement hydration inspired metakaolin to generate C-S-H gel and realized overall cementation of filter cake and cement sheath; 3) through select particle size of metakaolin matched with other solids in drilling fluid, drilling fluid performance index could meet requirements of engineering application; 4) and for best results, the circulation time of metakaolin drilling fluid should be more than 40 minutes. The results prove that metakaolin drilling fluid can improve the second interface cementation performance, showing feasibility on flied using and practical values on improving wellbore integrity.

Abstract: Due to the disadvantage of the traditional proppant, such as the low strength, poor acid corrosion resistance, embedding and flowback and so on, a new coated proppant was developed to deal with these problems. As the coating material, the natural gel was used to coat proppant. Different from the traditional mechanical mixing method, the means to make coated ceramic was the solvent dispersion method through the process of emulsification, cross-linking and dehydration dispersion. The strength of coated proppant was tested in different coated conditions. According to the result of test, the ceramic was coated under the optimum condition. Then the roundness, sphericity, acid solubility, crush resistance and surface structure of coated ceramic were compared with the uncoated ceramic. The experimental results showed that the optimal condition was as follows: 0.08 g/ml of gel concentration, 15/2 of ceramic/gel (g/g), 0.025 g/ml of emulsifier concentration, 20min of emulsifying time, 1/10 of water/oil rate. The coated ceramic prepared at this condition had the best performance, compared with the common ceramic, and its sphericity and acid solubility were greatly improved, bulk density reduced 7%. And the proppant surface was very smooth, the crush resistance was almost zero.

Abstract: Two kinds of nonionic surfactants were synthesized to configure fracturing fluid that can make up for the inadequacy of cationic surface active agent which has damage to the formation. The effect of the surfactant concentration on the apparent viscosity was discussed in this paper. The shear resistance, heat resistant, sand-carrying performance and gel breaking of the fracturing fluid were evaluated as well. It was shown that 2% of the surface active agent which was synthesized by oleic acid could crosslink in aqueous solution with the help of cosurfactant, and the viscosity could remain in 40mPa·s at 60°C, 170s^-1; 3% of the surface active agent which was synthesized by erucic acid could crosslink in aqueous solution with the help of cosurfactant, and the viscosity could remain in 45mPa·s at 90°C, 170s^-1. The elastic modulus G'≥2 and viscous modulus G"≥0.3 at 25°C and 0.01~10Hz frequency range showed that the fracturing fluid had good viscoelasticity. In the condition of 30°C, 70°C, sand sedimentation rates were 0.02 mm/s, 0.57 mm/s and 0.04 mm/s, 0.72 mm/s, meaning that the carrying capacity was perfect. The systems could be broken with kerosene, the gel breaking liquid was clarified and had no residue. So the fracturing fluids were suitable for the low and medium-high temperature formation.