At harsh conditions of high pressure high temperature (HPHT), polymers undergo thermal degradation leading to serious loss in fluid rheological and filtration properties. Nanoparticles are the most promising additives proposed to address this challenge. The stability of nanofluids is perused from various facets including rheological and filtration properties, shale stability, and zeta potential. The presence of nanoparticles could amazingly reduce the filtration at high temperatures even by 95%, and it also had a conspicuous effect on shale stability, thermal conductivity, and zeta potential. Experimental data were fit to rheological models to determine the best models describing the behavior of the nanosystem. It was clarified that the Sisko and Mizhari–Berk models enjoy the highest accuracy among the others. Moreover, a correlation is developed relating the viscosity of nanofluid to shear rate, temperature, and nanoparticles’ concentration. The model exposed high accuracy regarding a high value of average correlation factor, which was 0.994.

Many benefits by use of Oil-Based Mud (OBM) in drilling oil and gas wells have been identified in the oil industries worldwide. However the current ever increasing environmental legislations in preventing OBM application in the industries have dictated the use of water-based drilling fluid as the most environmentally acceptable alternative. On the other hand, drilling with water-based systems in shaly formations may cause many problems such as wellbore instability and high torque and drag. Therefore the most optimum alternatives would be different kinds of inhibited water-based systems in which adverse effects of shaly formations can also be controlled. These water-based alternatives are called High-Performance Water-Based Mud (HPWBM). Also the OBM properties is the final goal of the researchers to reach in their investigations to design a suitable HPWBM since OBM is the ideal drilling fluid to drill problematic formations.In this investigation attempts have been made to develop and formulate a water-based drilling fluid in which a suitable amine derivative has been successfully added to the system as a strong shale inhibitor agent instead of other conventional alternatives. Besides shale inhibition, an important challenge when using amine compounds in HPWBM is to overcome the thermal instability. Such a system must be formulated to achieve the right concentration of each mud additive to satisfy the necessity of a system that provides proper thermal stability during the drilling operation in high temperature sections. The newly HPWBM that was developed in this study comprises a specific concentration of a unique poly-ethoxylated alkyl diamine compound for shale inhibition, an amphoteric/polymeric shale encapsulator, a high-performance lubricant/deflocculating agent and special fluid loss additive to reach thermal stability up to 200°F. The designed system has exhibited optimum rheological properties and shale recovery in laboratory testing that was very close to that of OBM. The designed system has optimally improved the performance of previously formulated HPWBMs.

With increased concerns over the environmental issues regarding the use of oil-based mud (OBM)s, drilling companies in Iran are moving towards implementing less harmful water-based fluids. Due to low toxicity to the environment, effective shale inhibition and considerable cost savings, water-based glycol muds have the highest prospects as alternatives to OBMs in Iranian oilfields. However, designing water-based muds for drilling low-pressure shales may involve a compromise between mud weight optimization and overall environmental and economic advantages offered by these systems. The present study will focus on optimizing the weight of a glycol mud by emulsifying oil in the system and comparing its performance, environmental compatibility and cost with OBMs used in drilling low-pressure zones in Iranian oilfields. Properties of glycol solutions in the presence of oil were also evaluated. An emulsified glycol mud and an OBM with densities of 60 PCF were prepared and compared for their rheology and shale recovery. The shale recovery tests were conducted using shale samples from Maroon oilfield. Possible effects of contamination on the performance of the system were also studied. The glycol system was then treated to recover its diesel content. Overall, the laboratory data were convincing. With very low filtration rates, the emulsified glycol system is a candidate to replace OBMs in reservoir sections. Shale recoveries were comparable to those of OBMs. Compared with a similar OBM, considerable cost savings can be made and the system is more environmentally friendly. However, rheology was more difficult to control and the system was susceptible to contamination. Introduction Since their introduction in the 1930's, oil-based mud (OBM)s have played a major role in drilling troublesome shales. Their development was a milestone in drilling fluid technology as they help to maintain a smooth trouble-free drilling operation through shales. Practically, it is impossible for any water-based mud (WBM) to match the performance of OBMs. Excellent shale inhibition, wellbore stability, lubricity, anti-accretion properties, contamination resistance and possibility of reuse are the main advantages of OBMs over WBMs. Despite the above-mentioned benefits, their toxicity to the environment has limited their application in favor of environmentally-acceptable inhibitive WBMs. Both OBMs and cuttings contaminated with them are toxic discharge to the environment. Regulations restrict the way cuttings contaminated with OBMs can be discharged which may render their use uneconomic. This has paved the way towards replacing them with WBMs which are much more environmentally friendly. However, to replace OBMs, WBMs should have acceptable inhibition, lubricity, filtration and anti-accretion properties while having low toxicity to the environment. Inhibition is of prime importance for any alternative. Calcium, potassium and sodium salts, PHPA, polyglycols, silicates, amine compounds and formats are examples of chemicals which can be used to boost the inhibition properties of WBMs. Some inhibitive WBMs (e.g. Formate muds, KCl/Glycol and KCl/Silicate muds) have inhibition properties comparable to the OBMs. Beside inhibition, lubricity and anti-accretion are the other important properties of High Performance Water-Based Muds which are expected to perform similar to OBMs.