Introduction: An accurate HTHP rheological model of drilling fluids is critical for the safe and economic drilling operation. However, general HTHP rheological modeling methods appear to be very limited in the predictive accuracy. Materials and Method: In this work, a particular relative dial readings(RDR) modeling experiment was conducted on a weighted sulphonated water-based drilling fluid within a certain temperature and pressure range(30-150°C, 0.1-100MPa), in combination to dial reading data of six specific shear rates 3, 6, 100, 200, 300, and 600rpm, to develop a highly accurate HTHP rheological model. The RDR modeling procedure was investigated in details, including relative dial reading, Arrhenius relation, polynomial of pressure coefficients, and polynomial of shear rate coefficients. An equation relating RDR to temperature, pressure, and shear rate was determined. Results: The predictive deviation was calculated to be lower than 11.7%, and large errors occurred under the conditions of high pressure and low shear rates; all of which meet the requirement of in-field predictive accuracy. These results not only provide an accurate HTHP rheological equation for the weighted sulphonated water-based drilling fluid, but also propose an effective HTHP rheological modeling strategy for drilling fluids.

Curing minor leaks and restoring the integrity of a wellbore in a safe and economical way is always challenging in oil and gas production. In this work, a composite pressure-activated sealant, combined with liquid and solid sealing materials, was prepared via the demulsification approach. The structure, morphology, and size distribution of key particulates in the sealant were examined, and the in-situ self-adaptive sealing property was examined with a specially design dynamic sealing detector. The results indicated that the pressure-activated sealant was a multi-dispersed phase system, and the dispersed colloid particles were regular in shape and had a narrow size distribution of 300–400 μm. The solid sealing materials were introduced to construct a composite pressure-activated sealant, and the sealing capability can be markedly reinforced by cooperativity of liquid and solid sealing materials. A mechanochemical coupling model was put forward to rationalize the dynamic sealing process. Finally, such sealant system was employed in a certain offshore gas well with sustained casing pressure to verify its applicability in minor defect repairs.

Introduction: The production casing of 3% Cr steel has encountered severe internal corrosion in Huizhou Oilfield. To disclose corrosion behavior of inner casing, a series of corrosion exposure tests were systematically conducted on 3% Cr coupons in terms of in-field conditions.Material and Methods: Influence of exposure time, temperature, and water-cut on the CO₂corrosion of 3% Cr steel was investigated, and analyses on weight loss, composition and morphology of corrosion product, and Tafel polarization curves were further carried out.Result: The results showed that the corrosion rate of 3% Cr steel increased with increasing temperature, but such trend descended when the temperature exceeded 65°C due to formation of an compact and adherent corrosion product film on the surface of 3% Cr coupons. While varying exposure time from 7 days to 14 days, the corrosion rate decreased, and the Cr and O enrichment was determined in the corrosion products. The corrosion rate of 3% Cr steel increased with a continuous increment of water-cuts, especially when the water-cut was larger than 40%.Conclusion: The localized corrosion can happen at the lower water-cut due to the presence of amorphous films. The main corrosion products were FeCO₃, Cr5O₁₂, Fe2O3, and Fe-Cr. Entry of CO₂to the simulated formation water caused an increase in the anodic Tafel slope, and accelerated dissolution of 3% Cr steel.