Magnesium Oxychloride and Magnesium Oxysulfate Cements as Temporary Plugging Agents in Geothermal Drilling.

The development and utilization of geothermal resources are effective ways to alleviate the current haze situation, adjust the energy structure, and achieve energy conservation and emission reduction. Geothermal formations typically contain extensive fracture networks, with fracture openings. These fracture networks can result in substantial losses of the drilling fluid and increased costs for geothermal drilling. Temporary plugging cements are used to solve the problem of lost circulation due to their high strength and high acid solubility. In this paper, two types of temporary plugging materials, magnesium oxysulfate (MOS) cement and magnesium oxychloride (MOC) cement, were prepared. The influence of the plugging agent on the flow field and the force exerted on the solid under the action of the fluid was analyzed using fluid-solid coupling software. The simulation results show that when subjected to a flow rate of 10 m/s, the edge of the cement experiences a significant force, while the stress is not widely transmitted to the middle and rear of the cement. This indicates that the cement has a strong resistance to the fluid flow. The fundamental characteristics of MOC cement and MOS cement, such as compressive strength and setting time, were investigated. The test results show that adjusting the molar ratio of the two types of cements can shorten the setting time by 60% and increase the compressive strength to up to 23 MPa. In addition, the acid solubility of the cement with different ratios of raw materials is above 95%. The plugging performance of these two cements as loss circulation materials was evaluated by using a physical simulation device. The pressure bearing capacity of the MOC cement with different MgO/MgCl2·6H2O/H2O molar ratios ranged between 13.4 and 23.6 MPa. The maximum bearing capacity of the MOS cement can reach up to 18.6 MPa. The results showed that both cements possess excellent plugging and pressure bearing capacity.

Recent advances in the applications of graphene materials for the oil and gas industry.

Graphene is a material formed with carbon atoms connected by sp2 hybridization. It is extremely strong and very ductile, and is superhydrophobic and superlipophilic. It has important application prospects in materials science, micro and nano processing, energy, aerospace and biomedicine. Graphene also has some applications in the petroleum industry. As nanoscale materials, graphene-based materials can plug nano-pores and prevent water intrusion into clay minerals during the drilling process, they are suitable for sliding between layers and can be used as lubricants due to the two-dimensional structure. The adsorption properties of graphene-based materials allow them to improve the treatment rate when treating oily wastewater. This paper compiles recent advances in the application of graphene and its derivatives in oilfield extraction, including improving drilling fluid performance, enhanced oil recovery and oily wastewater treatment. We compare the performance advantages of graphene-based materials over other additives, and summarize the mechanism of action of graphene-based materials. The shortcomings of current research are identified and future research and improvement directions are envisaged.

A novel choline chloride/graphene composite as a shale inhibitor for drilling fluid and the interaction mechanism.

For wellbore stability in shale formations, the development of environmentally friendly and efficient shale inhibitors is urgently needed. Herein, we report the preparation of choline chloride-modified graphene (Ch-G). The inhibition and interaction mechanisms of choline chloride-modified graphene on montmorillonite were also investigated. We evaluated the inhibition of Ch-G via linear swelling and rolling recovery and selected the inorganic salt inhibitor KCl as the control group. The lowest swelling height of 2.10 mm and the highest rolling recovery of 78.87% were achieved, indicating the excellent inhibition performance of Ch-G. The mechanism of inhibition of Ch-G was determined by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. The Ch-G formed hydrogen bonds, coordination, and electrostatic interactions with the surface of montmorillonite and entered the montmorillonite via intercalation to achieve the inhibition. The increase in the nitrogen atom content in Ch-G led to the production of more positive ions and the formation of more ion bands, which enhanced the ability to inhibit shale hydration. The addition of Ch-G produced larger montmorillonite sheets, demonstrating its effective inhibition ability, which is needed to enable drilling fluids to stably drill into shale formations.

Experimental Study on the Polymer/Graphene Oxide Composite as a Fluid Loss Agent for Water-Based Drilling Fluids.

The wellbore instability caused by the penetration of drilling fluids into the formation is a vital problem in the drilling process. In this study, we synthesized a polymer/graphene oxide composite (PAAN-G) as a fluid loss additive in water-based drilling fluids. The three monomers (acrylamide (AM), 2-acrylamide-2-methyl-1-propane sulfonic acid (AMPS), N-vinylpyrrolidone (NVP)) and graphene oxide (GO) were copolymerized using aqueous free radical polymerization. The composition, micromorphology, and thermal stability properties of PAAN-G were characterized by Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA). According to the American Petroleum Institute (API) standards, the influence of PAAN-G on the rheological and filtration properties of bentonite-based mud was evaluated. Compared with PAAN, PAAN-0.2G has more stable rheological properties at high temperatures. The experimental results showed that even at a high temperature of 240 °C, PAAN-G can still maintain a stable fluid loss reduction ability. In addition, PAAN-G is also suitable for high-salt formations; it can still obtain satisfactory filtration volume when the concentration of sodium chloride (NaCl) and calcium chloride (CaCl2) reached 25 wt %. Besides, we discussed the fluid loss control mechanism of PAAN-G through particle size distribution and scanning electron microscopy (SEM).