In order to develop high-performance water-based drilling fluid with the aim of meeting the increasing requirement of drilling industry, highly inhibitive and high-temperature-resistant shale inhibitors are essential. In this study, 4, 4 0 -methylenebis-cyclohexanamine was introduced as a potential shale inhibitor. The inhibitive properties of the amine compound in comparison with currently available polyether diamine inhibitor were evaluated using bentonite inhibition test, shale cuttings hot-rolling dispersion test, linear swelling test, and pressure transmission test. The inhibitive mechanism was investigated with zeta potential measurement, X-ray diffraction analysis, and contact angle measurement. The results indicated that 4, 4 0 -methylenebis-cyclohexanamine can inhibit shale hydration and dispersion effectively, and prevent pressure transmission to a certain extent, performing better than that of polyether diamine. Furthermore, the new diamine provides reliable thermal stability as high as 220°C, preserving the benefits of high-temperature wells application. This novel diamine inhibits shale hydration and dispersion with the combination of chemical inhibition and physical plugging. The intercalation into the interlayer of clay with monolayer collapses the hydrated clay structure and expels the water molecules. After adsorption, clay surface became more hydrophobic, which prevents the imbibition of water. The variation of solubility separates the compound from the solution, which can plug the micro-pores of shale and prevent fluid invasion.

Dendrimers have been paid increasing attention in the area of drilling fluid recently due to their unique structure and properties. The inhibitive properties of amine terminated polyamidoamine (PAMAM) dendrimers ranging from G0 to G5 were evaluated by relative inhibition rate, shale cuttings hot-rolling dispersion test and particle size distribution measurement respectively. Meanwhile the inhibitive capacity of the polymers under various pH value conditions was studied. The interaction between sodium bentonite and PAMAM dendrimers was characterized by zeta potential measurement and X-ray diffraction (XRD). The results indicated that, G0 and G5 are superior to polyether diamine, while G1, G2, G3 and G4 perform better than KCl. PAMAM dendrimers from G0 to G5 can decrease the zeta potential of clay particles from-39 mV to about-22.6 mV at natural pH values and reverse the charge when the pH value is adjusted to 9. When intercalated into the clay interlayer in aqueous solution, the candidate PAMAM dendrimers can form monolayer arrangement at lower concentrations and reduce the interlayer spacing of hydrated clay from 1.95 nm to 1.38-1.63 nm, which is the direct evidence of inhibiting shale hydration. With the increase of

Featured Application: This work aims to simultaneously realize good encapsulation performance and low-temperature rheological property for deepwater drilling fluid. It is expected to be used in deepwater oil and gas drilling operations. Abstract:In deepwater oil and gas drilling, the high-molecular-weight encapsulator aggravates the thickening of the drilling fluid at low temperatures. Therefore, it is hard to manage the downhole pressure, and drilling fluid loss occurs. In this paper, a zwitterionic polymer P(AM-DMC-AMPS) which was the terpolymer of acrylamide, methacrylatoethyl trimethyl ammonium chloride, and 2-acrylamido-2-methylpropane sulfonic acid, was developed as a low-molecular-weight encapsulator. It was characterized by Fourier transform infrared spectrum analysis, nuclear magnetic resonance, and gel permeation chromatography. Moreover, the low-temperature rheology, shale inhibition and filtration properties of water-based drilling fluids (WBDFs) containing different encapsulators were experimentally investigated and compared. The results showed that the molecular weight of P(AM-DMC-AMPS) was about 260,000, much lower than that of the conventional encapsulators. In the deepwater drilling temperature range 4-75 • C, WBDF containing P(AM-DMC-AMPS) had lower and more stable rheological property because of its short molecular chains. The high shale recovery rate and low swelling rate indicated its strong shale inhibition performance, owing to its adsorption on the clay surface and the wrapping effect through both hydrogen bonding and electrostatic interaction. It also improved the filtration property of WBDF, and was compatible with other WBDF components. This product is expected to simultaneously realize the good encapsulation performance and low-temperature rheological property for deepwater drilling fluid.

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Filtration loss control under high-temperature conditions is a worldwide issue among water-based drilling fluids (WBDFs). A core–shell high-temperature filter reducer (PAASM-CaCO3) that combines organic macromolecules with inorganic nanomaterials was developed by combining acrylamide (AM), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), styrene (St), and maleic anhydride (MA) as monomers and nano-calcium carbonate (NCC). The molecular structure of PAASM-CaCO3 was characterized. The average molecular weight of the organic part was 6.98 × 105 and the thermal decomposition temperature was about 300 °C. PAASM-CaCO3 had a better high-temperature resistance. The rheological properties and filtration performance of drilling fluids treated with PAASM-CaCO3 were stable before and after aging at 200 °C/16 h, and the effect of filtration control was better than that of commonly used filter reducers. PAASM-CaCO3 improved colloidal stability and mud cake quality at high temperatures.