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.

A novel graphene/triolein complex-based lubricant for improving high temperature water-based drilling fluid.

Drilling engineering plays a pivotal role in the exploration and extraction of subsurface resources. It heavily depends on drilling fluid, which serves various essential functions including cooling the drill bit, removing drilled cuttings, maintaining formation pressure equilibrium, stabilizing the wellbore, transmitting hydraulic pressure, and safeguarding oil and gas reservoirs. Nonetheless, drilling fluid encounters multiple obstacles such as leakage control, waste fluid management, prevention of wellbore collapse, avoidance of hole enlargement, and environmental preservation. In order to surmount these challenges, the introduction of lubricants into the drilling fluid yields a multitude of advantages, encompassing equipment safeguarding, enhanced drilling efficiency, preservation of wellbore integrity, and bolstered drilling safety. These factors hold crucial significance in ensuring the triumph of drilling operations. This paper presents the introduction of a new lubricant derived from triolein. Following the preparation of graphene and triolein, they were incorporated into the drilling fluid system. A set of tests was subsequently conducted after aging at 240 °C for 16 hours. To assess the impact of the lubricant on the drilling fluid, an examination of rheological and filtration properties was conducted. Additionally, investigations into the friction coefficient, adhesion coefficient, and extreme pressure lubricity were carried out to evaluate the lubricating performance of the drilling fluid. Adding lubricants at a temperature of 240 degrees Celsius has successfully controlled the adhesion coefficient of the drilling fluid to below 0.2, reaching a minimum of 0.055, resulting in a reduction rate of over 70%. This indicates that the lubricant performs well at high temperatures, effectively reducing friction and enhancing drilling speed.

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 hyperbranched polyethyleneimine-graphene composite as shale inhibitor for drilling fluid.

One of the principal conundrums in drilling operations is addressing wellbore instability caused by shale hydration. Therefore, it is crucial to develop high-performance shale inhibitors. In this work, a hyperbranched polyethyleneimine/graphene composite (HPEI-G) was prepared by blending at 60 °C, and it was then used as a shale inhibitor. The inhibition performance of HPEI-G was verified using mud making test, linear swelling test and sedimentation test. The mechanism of HPEI-G was researched and determined using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), particle size distribution test and scanning electron microscopy (SEM). The compatibility of HPEI-G with the basic water-based drilling mud (WBM) was also verified. It can be observed from the results of the linear swelling test that 0.5 wt% HPEI-G reduced the swelling rate of montmorillonite (MMT) to 30.36%, and 1 wt% of KCl only decreased the swelling rate of MMT to 43.83%. In addition, HPEI-G is compatible with WBDF. The inhibition mechanism of HPEI-G included chemical adsorption and physical blockage. HPEI-G was adsorbed on the surface and interlayer of MMT by hydrogen bonding and electrostatic attraction, reducing the diffuse electric double layer to inhibit the hydration of MMT. The sheets of graphene in HPEI-G allowed it to stick on the surface of the shale and plug the nanopores of the shale, preventing the access of water. The inhibition effect of HPEI-G over a temperature range from room temperature to 150 °C was considered to be excellent.

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.

Advanced developments in environmentally friendly lubricants for water-based drilling fluid: a review.

The problem of high friction and high torque is one of the most troublesome problems for engineers in extended reach wells and long horizontal wells. Generally, the friction coefficient of oil-based drilling fluid is around 0.08, while the friction coefficient of water-based drilling fluid exceeds 0.2, which is much higher than that of oil-based drilling fluid. With the increasingly stringent environmental regulations, water-based drilling fluids have gradually become a better choice than oil-based drilling fluids. Therefore, lubricants become a key treatment agent for reducing the friction coefficient of water-based drilling fluids. Although there have been many related studies, there is a lack of comprehensive reviews on environmentally friendly water-based drilling fluid lubricants. In general, water-based drilling fluid lubricants can be mainly divided into solid lubricants, ester-based lubricants, alcohol-based lubricants, and nano-based lubricants. Vegetable oil ester-based lubricants, biodiesel lubricants, and dispersible nano-lubricants are all promising environmentally friendly water-based drilling fluid lubricants. Understanding the lubrication mechanism of different types of lubricants and clarifying the evaluation methods of lubricants is an important prerequisite for the next development in high-performance water-based drilling fluid lubricants. Therefore, the purpose of this paper is to give a comprehensive overview of water-based drilling fluid lubricants in recent years, in order to fully understand the development and lubrication mechanism of water-based drilling fluid lubricants, and provide new ideas for subsequent research on water-based drilling fluid lubricants.

An Inverse Emulsion Polymer as a Highly Effective Salt- and Calcium-Resistant Fluid Loss Reducer in Water-Based Drilling Fluids.

To control the fluid loss of water-based drilling fluids (WBDFs) in salt-gypsum formations, a nano-SiO2 graft copolymer was prepared by inverse emulsion polymerization. The polymer (EAANS) was prepared with acrylamide, 2-acrylamido-2-methyl-1-propane sulfonic acid, N-vinylpyrrolidone, and KH570-modified nano-silica (M-SiO2) as raw materials. The molecular structure and morphology of EAANS were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, transmission electron microscopy (TEM), and other methods. In the temperature range of 150 °C, 2 wt % EAANS can reduce the API filtration volume of the base slurry to within 20 mL and the HP-HT filtration volume at 150 °C to 21.8 mL. More importantly, 2 wt % EAANS can maintain the API filtration volume less than 10 mL even when the concentration of NaCl or CaCl2 was as high as 36 or 30 wt %, and as the salt/calcium content increased, the amount of filtration continued to decrease. The results of TEM, X-ray diffraction, particle size distribution, and scanning electron microscopy showed that the fluid loss control mechanism of EAANS was that EAANS can form a crosslinked network structure in the solution and adsorb on the clay surface, so as to reduce the particle size of clay particles, increase the proportion of fine particles in drilling fluids, and finally form a dense filter cake to reduce the filtration volume. Because of the excellent filtration performance of EAANS at high Na+/Ca2+ concentration, EAANS can become a promising WBDF fluid loss reducer in salt-gypsum 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).

Comparison of an Emulsion- and Solution-Prepared Acrylamide/AMPS Copolymer for a Fluid Loss Agent in Drilling Fluid.

Acrylamide polymers were widely used as oilfield chemical treatment agents because of their wide viscosity range and versatile functions. However, with the increased formation complexity, their shortcomings such as poor solubility and low resistance to temperature, salt, and calcium were gradually exposed. In this paper, acrylamide (AM)/2-acrylamide-2-methyl-1-propane sulfonic acid (AMPS) copolymers were synthesized by aqueous solution polymerization and inverse emulsion polymerization, respectively. The aqueous polymer (W-AM/AMPS) and the inverse emulsion polymer (E-AM/AMPS) were characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (1H NMR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and particle size analysis. The rheological properties, filtration properties, and sodium ion (Na+) and calcium ion (Ca2+) resistance were investigated. The results showed that E-AM/AMPS not only had a dissolution speed 4 times faster than that of W-AM/AMPS but also had superior shear-thinning performance both before and after aging. The filtration property of the bentonite system containing 2 wt % E-AM/AMPS was also better than that of the bentonite system containing 2 wt % W-AM/AMPS. In addition, E-AM/AMPS also exhibited extremely high tolerance for Na+ and Ca2+. The huge difference between rheological and filtration properties of E-AM/AMPS and W-AM/AMPS in drilling fluid can be attributed to the differences in the polymer microstructure caused by the two polymerization methods. Both FTIR and 1H NMR results showed that more hydrogen bonds were formed between E-AM/AMPS molecular groups and molecular chains, which led to a cross-linked network structure of E-AM/AMPS which was observed by TEM. It was this cross-linked network structure that made E-AM/AMPS have a high viscosity and allowed it to be better adsorbed on bentonite particles, thus exhibiting excellent rheological and filtration behavior. In addition, E-AM/AMPS powder had a high specific surface area so that it can be dissolved in water faster, greatly reducing the time and difficulty of configuring drilling fluid.

Synthesis of a Biodegradable and Environmentally Friendly Shale Inhibitor Based on Chitosan-Grafted l-Arginine for Wellbore Stability and the Mechanism Study.

We synthesized a biodegradable and environmentally friendly shale inhibitor based on chitosan-grafted l-arginine (CA) for wellbore stability in shale formation. The structure of CA was characterized by Fourier-transform infrared spectroscopy. Linear swelling, shale hot-rolling recovery, shale inhibition durability, and sedimentation experiments were used to evaluate the inhibition properties of CA and compared with the commonly used inhibitors potassium chloride (KCl) and polyamines (HPA and SIAT). The results showed that the inhibition of CA was better than that of KCl, HPA, and SIAT and that it can have a shale hot-rolling recovery of more than 90% at 150 °C, which indicated that CA had higher temperature resistance and longer durability. More importantly, it can be biodegraded as exhibited by the biodegradibility experiment. The inhibition mechanism of CA was studied by particle size distribution, X-ray diffraction, scanning electron microscopy, zeta potential analysis, and contact angle test. The strong inhibition of CA can be attributed to its encapsulation of MMT and shale surfaces. The CA with strongly positively charge was firmly adsorbed on the surface of MMT and shale, which not only neutralized the negative charge of MMT, compressed the diffused electric double layer, but also increased the contact angle of MMT and shale surface which enhancing hydrophobicity of MMT and shale. The hydration swelling and dispersion of MMT and shale were further inhibited. In addition, compatibility experiments showed that CA was compatible with commonly used treatment agents. CA did not affect the rheology of water-based drilling fluids and can reduce fluid loss after aging.

Micro-manganese as a weight agent for improving the suspension capability of drilling fluid and the study of its mechanism.

The contradiction between the sag stability of weighted materials and the rheological properties of drilling fluids is one of the main technical difficulties in high-density drilling fluids. Thus, understanding the suspension mechanism of weighting materials is the key to improving the sag stability of weighting materials. In this study, micro-manganese (Mn3O4) was compared with the commonly used weighting agent barite to study the suspension mechanism of Mn3O4. The weighting effect of Mn3O4 and barite was evaluated by static and dynamic sag tests, rheological property measurements and filtration property tests. The evaluation experiment results showed that the sag stability of Mn3O4 was better than that of barite, and Mn3O4 could significantly increase the suspension capacity of drilling fluids and improve their rheology property. The scanning electron microscopy (SEM) and other test results indicate that the small and uniform spherical structure of micro-manganese not only causes it to have less friction, but also intense Brownian motion in drilling fluid, which weakens the sag caused by gravity. The large specific surface area of Mn3O4 results in the strong adsorption of water molecules and polymers in drilling fluids, resulting in the formation of a hydrated film on the surface of the Mn3O4 particles and physical crosslinking with polymer chains. This prevents sagging caused by the adsorption of small particles to form large particles. The key findings of this work are expected to provide a basis for improving the sag stability of weighting materials in drilling fluids and better the application of micro-manganese in drilling fluids.

A turn-on fluorescent sensor for pyrophosphate based on the disassembly of Cu2+-mediated perylene diimide aggregates.

A complex between an anionic perylene diimide derivative (PDI-GlyAsp) and cupric ion has been prepared and applied to be turn-on fluorescent probe for the detection of pyrophosphate (PPi) in 100% aqueous solution. The complex formation process and PPi detection have been studied by absorption and emission spectroscopy. It was confirmed that the introduction of cupric ion into PDI-GlyAsp solution resulted in the assembly of PDI-GlyAsp into PDI-GlyAsp/Cu(2+) aggregates, leading to the fluorescence quenching of PDI-GlyAsp. Upon addition of PPi into the above solution led to the disassembly of the aggregates due to the competitive binding of PPi with Cu(2+) in the PDI-GlyAsp/Cu(2+) complex, and a recovery of PDI-GlyAsp emission was observed. Therefore, the PDI-GlyAsp/Cu(2+) complex can be applied as a turn-on fluorescent probe for detecting PPi with high selectivity and sensitivity.