Janus amphiphilic graphene oxide (JAGO), modified by dodecylamine on one side of graphene oxide (GO), was investigated for its novel use as a shale inhibitor. JAGO was synthesized by the Pickering emulsion template technology and was characterized by the Fourier-transform infrared spectra, UV-vis spectra, and transmission electron microscopy. Compared to KCl (5%), polyether diamine (2%), and pristine GO (0.2%), JAGO's highest shale recovery rate (75.2% at 80 • C) and lowest swelling height of Mt-pellets (2.55 mm, 0.2%) demonstrated its excellent inhibitive property. Furthermore, JAGO acted as a perfect plugging agent and greatly reduced filtration loss. Based on the results of X-ray diffraction, contact angle measurements, and pressure transmission tests, we proposed that the 2D nano-sheet amphiphilic structure of JAGO, which enabled it to be effective both in chemical inhibition and physical plugging, was responsible for its remarkable inhibition performances.
In drilling deep complex formations, most drilling fluid additives have insufficient temperature and salt tolerance, resulting in the decline of drilling fluid performance. This study used 2-acrylamide-2-methylpropane sulfonic acid, acrylamide, dimethyl diallyl ammonium chloride and modified nano-laponite to synthesize a nanocomposite filtrate reducer (ANDP) with excellent temperature and salt resistance, which can maintain the performance of drilling fluid. The structure of ANDP was analysed by a transmission electron microscope and an infrared spectrometer. The thermal stability of ANDP was studied by thermogravimetric analysis. The performance of ANDP was evaluated in a water-based drilling fluid. The mechanism was analysed per clay particle size distribution, Zeta potential, filter cake permeability and scanning electron microscopy imaging. The results show that ANDP has good thermal stability and the expected molecular structure. The filtration of freshwater drilling fluid after ageing at 200°C is 10.4 ml and that of saturated brine drilling fluid is 6.4 ml after ageing at 150°C. Mechanism analysis suggests that the ANDP increases the thickness of clay particle hydration layer and maintains the colloidal stability of the drilling fluid. ANDP inhibits the agglomeration of clay particles and significantly reduces the filtration by forming dense mud cake.
When it comes to ultra-deep wells drilling, there are multiple difficulties to be considered: over-pull and blockage during tripping because of swelling of shale and clay, instability, and costly maintenance of traditional water-based drilling fluid in high temperature. In order to solve these problems, a completely cationic drilling fluid system with excellent inhibition and stability in ultra-deep wells has been researched.The completely cationic drilling fluid system, characterized by a zero zeta potential differential between the fluid system and the formation to which it is applied, consists of cationic inhibitors, cationic coating agents, cationic fluid loss additives, cationic plugging agents, etc. Laboratory experiments have shown that the zeta potential of the optimal fluid system lies between Ϫ10 mV and Ϫ20 mV, which is slightly higher than that of the formation. Furthermore, the system exhibited excellent rheology properties, filtration control properties, and anti-contamination abilities of salt, calcium, and clay at 180°C.The completely cationic drilling fluid was successfully applied to more than 30 wells in an Haxinre oil reservoir located in the central of Tarim basin with depths over 6650 m and temperatures Ͼ160°C. The results show that the completely cationic fluid has particularly good inhibition, rheology, and filtration control properties at high temperatures, while it resists salting, clay, and gypsum contamination effectively. Compared with traditional fluid systems, wells using completely cationic fluids have~10% fewer drilling problems,~15% greater penetration rates, and~10% reduced drilling periods. The best records include 59 days to finish drilling a 6700-m-deep well and 69 days for a 7300-m-deep well, which were about 30 -50 days earlier than planned.It is clear that the completely cationic drilling fluid system is an economic alternative for ultra-deep reservoir drilling.
The southwest area of Tarim has good potential for exploration and development, but the geological conditions of Yingsha block are complicated and complex conditions occurred frequently in drilling operations. There were 11 times lost circulation, which ranged from N2a to E1a and the lithology ranged from mudstone and sand-mudstone interbeds to gypsum rock, and the drilling cycle is up to 719 days, which seriously restricts the exploration and development of oil and gas resources. In this paper, the rock mineral composition and physical and chemical characteristic profiles of the whole well have been established for the well drilled in this area. The characteristic profiles show that quartz (21.4%~57.4%) and clay minerals (17%~44.9%) are the main layers in the lower strata (5069 m-7015 m) drilled in Yingsha. The clay minerals are dominated by illite (58%~85.75%) without smectite. The highest proportion of illite/smectite formation is 25%, the highest expansion rate is 23.87%, and the lowest recovery rate is 3%. Therefore, the stratum has strong hydration and dispersion characteristics. The average porosity of 4064 m-6666.5 m is 1.86%-6%, and the formation cracks are well developed. The wellbore instability mechanism in Yingsha is the good physical property of the sandstone, the development of cracks and micro-cracks in the lower strata, the broken strata, and the strong hydration and dispersion ability. The performance evaluation of KCL-Polysulfonate drilling fluid used in Yingsha shows that the recovery rate increases to more than 80% when the amount of KCL is 7–10%. With the introduction of paraffin nano-emulsion, the filtration loss is reduced by 30%, and the inhibition and plugging performance of drilling fluid is further improved.
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