Guancheng Jiang

Biodegradation of partially hydrolyzed polyacrylamide by bacteria isolated from production water after polymer flooding in an oil field.

Partially hydrolyzed polyacrylamide (HPAM) in production water after polymer flooding in oil filed causes environmental problems, such as increases the difficulty in oil-water separation, degrades naturally to produce toxic acrylamide and endanger local ecosystem. Biodegradation of HPAM may be an efficient way to solve these problems. The biodegradability of HPAM in an aerobic environment was studied. Two HPAM-degrading bacterial strains, named PM-2 and PM-3, were isolated from the produced water of polymer flooding. They were subsequently identified as Bacillus cereus and Bacillus sp., respectively. The utilization of HPAM by the two strains was explored. The amide group of HPAM could serve as a nitrogen source for the two microorganisms, the carbon backbone of these polymers could be partly utilized by microorganisms. The HPAM samples before and after bacterial biodegradation were analyzed by the infrared spectrum, high performance liquid chromatography and scanning electronic microscope. The results indicated that the amide group of HPAM in the biodegradation products had been converted to a carboxyl group, and no acrylamide monomer was found. The HPAM carbon backbone was metabolized by the bacteria during the course of its growth. Further more, the hypothesis about the biodegradation of HPAM in aerobic bacterial culture is proposed.

Nano-fluid loss agent based on an acrylamide based copolymer “grafted” on a modified silica surface

In this paper, the nano copolymer of acrylamide (AM), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and modified nano-silica (M-SiO2) was synthesized by free radical polymerization in a water solution. The addition of ethanol was used to control the molecular weight of the copolymer. The characterization of the copolymer was measured by Fourier transform infrared spectroscopy, a particle size analyzer, transmission electron microscopy, atomic force microscopy and nuclear magnetic resonance. AM and AMPS were grafted on the surface of M-SiO2 successfully. The grafted copolymer was in nm size not only in the water solution but also in a drilling fluid. Filtration properties and the interaction mechanism of the copolymer with montrillonite (MMT) were studied in a fresh water drilling fluid system and different kinds of salt water drilling fluid systems. The copolymer as fluid loss agent was equal to commonly used fluid loss agents in a fresh water drilling fluid system. The resistance properties to salinity, calcium and high temperature were tested. The copolymer had a resistance temperature of 150 °C and saturated brine resistance. The resistance property to calcium was up to 1 wt%. The interaction mechanism between montrillonite and the copolymer was evaluated using a particle size analyzer, transmission electron microscopy, scanning electron microscopy and a surface area analyzer. The copolymer was adsorbed on the surface of MMT. Compared to pristine MMT, the addition of the copolymer resulted in new peaks in the particle size analyzer image. The filter liquor of the drilling fluid with the copolymer showed two peaks in nm scale and the filter liquor of the drilling fluid without the copolymer showed that no peak appeared under 1000 nm. The results presented that the copolymer as a fluid loss agent was a nano material in the drilling fluid. The surface area analyzer (BET) results showed that the surface area of a natural rock reduced after treatment with the copolymer, indicating that the copolymer entered into the nanopores of shale because of the adsorption on the surface of shale.

Prediction of reservoir sensitivity using RBF neural network with trainable radial basis function

Reservoir sensitivity prediction is an important basis for designing reservoir protection program scientifically and exploiting oil and gas resources efficiently. Researchers have long endeavored to establish a method to predict reservoir sensitivity, but all of the methods have some limitations. Radial basis function (RBF) neural network, which provided a powerful technique to model non-linear mapping and the learning algorithm for RBF neural networks, corresponds to the solution of a linear problem, therefore it is unnecessary to establish an accurate model or organize rules in large number, and it enjoys the advantages such as simple network structure, fast convergence rate, and strong approximation ability, etc. However, different radial basis function has different non-linear mapping ability, and different data require different radial basis functions. Nowadays, the choice of radial basis function in the network is based on experience or test result only, which exerts a great adverse impact on the network performance. In this study, a new RBF neural network with trainable radial basis function was proposed by the linear combination of common radial basis functions. The input parameters of the network were the influence factors of reservoir sensitivity such as porosity and permeability, etc. The output parameter was the corresponding sensitivity index. The network was trained and tested with the data collected from our own experiments. The results showed that the new RBF neural network is effective and improved, of which the accuracy is obviously higher than the network with single radial basis function for the prediction of reservoir sensitivity.

Wettability alteration to intermediate gas-wetting in low-permeability gas-condensate reservoirs

Gas-condensate reservoirs experience significant productivity losses as reservoir pressure drops below the dew point due to condensate accumulation and water blocking and the subsequent reduction in gas relative permeability. One potential way to overcome this problem is to alter reservoir wettability to gas-wetting to reduce condensate accumulation and water blocking in the near wellbore and maintain high productivity. The major goal of this work was to study the mobility of the gas and liquid phase (both water and oil) before and after wettability alteration from strong liquid-wetting to intermediate gas-wetting. For this purpose, in addition to relative permeability measurements, we also conducted various other tests to demonstrate that liquid mobility can be improved significantly due to wettability alteration. As wettability modifiers, fluorinated polymers are capable of delivering a good level of oil and water repellency to the rock surface, making it intermediate gas-wet and alleviating such liquid blockage under high temperature. The contact angle analyses, capillary rise, flow tests, and imbibition spontaneous tests were used to estimate the effect of treatments on wettability. Experimental results demonstrated that the fluorinated polymers can alter the wettability of cores from strong liquid-wetting to gas-wetting, which could decrease the amount of water invaded and resided in the gas formation. Core flood test results demonstrated that the relative permeabilities of both the gas and the liquid phases were increased significantly after the wettability alteration to preferential gas-wetness. The residual liquid saturation was decreased, and the gas production was enhanced greatly due to the wettability alteration. These results imply that gas well deliverability may increase substantially when wettability is altered to intermediate gas-wetting. Efficiency in the extraction of natural gas is important to improve the productivity of gas-condensate reservoirs where liquid accumulates, which is beneficial for the economic and environmental considerations of the oil and gas industry.

Evaluation of gas wettability and its effects on fluid distribution and fluid flow in porous media

The special gas wettability phenomenon of reservoir rocks has been recognized by more and more researchers. It has a significant effect on efficient development of unconventional reservoirs. First, based on the preferentially gas-covered ability and surface free energy changes, definition and evaluation methods have been established. Second, a method for altering rock wettability and its mechanisms have been studied, surface oriented phenomena of functional groups with low surface energy are the fundamental reason for gas wettability alteration of rock. Third, the effect of gas wettability on the surface energy, electrical properties and dilatability are investigated. Last, the effects of gas wettability on capillary pressure, oil/gas/water distribution and flow are investigated with capillary tubes and etched-glass network models. The gas wettability theory of reservoir rocks has been initially established, which provides theoretical support for the efficient production of unconventional reservoirs and has great significance.

A biomimetic drilling fluid for wellbore strengthening

Abstract Based on biomimetic technology, wellbore strengthener GBFS-1 and shale inhibitor YZFS-1 were synthesized imitating the mussel protein which has super adhesion. A new drilling fluid system centering on the two biomimetic agents was designed and prepared in order to enhance the strength of shale rocks near wellbore and maintain wellbore stability. Various inhibition evaluation tests show that YZFS-1 can strongly inhibit clay hydrated swelling and the resulting shale dispersion, due to the adsorption and self-polymerization of YZFS-1 molecules in the interlayer of clay. Besides the ability of controlling fluid loss, GBFS-1 can also adhere to shale rock, produce dense and water impermeable biomimetic shell that has relative strong cohesion strength after spontaneous cure. The shear strength tests show that the shear strength of two shale pieces glued together by the biomimetic shell in aqueous environment is obviously stronger than glued by several commonly-used binders. Through compatibility evaluation and dosage optimization of the additives, the formula of biomimetic drilling fluid was established, and its performance was evaluated and compared with another anti-caving drilling fluid. The results show the biomimetic drilling fluid is better in all basic performances than the anti-caving drilling fluid on the whole, and can effectively inhibit shale swelling and dispersion.

Biodegradable oligo (poly-L-lysine) as a high-performance hydration inhibitor for shale

Oligo (poly-L-lysine) (OPLL), utilized as a high-performance inhibitor for the hydration of shale, was synthesized with L-lysine as a monomer by the thermal copolymerization method. OPLL was characterized through Fourier-transform ion cyclotron resonance mass spectroscopy (FT-ICR-MS), nuclear magnetic resonance hydrogen spectroscopy (1H NMR), Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetry (TG). The inhibition performance of OPLL was evaluated through the combination of montmorillonite (MMT) linear swelling, MMT dispersion and shale dispersion tests, and these results were compared with those for other commonly-used inhibitors in the field. The results demonstrated that OPLL possessed an outstanding inhibition effect on the hydrated dispersion of both MMT-rich and illite-rich shale that was superior to many commonly-used shale inhibitors such as KCl, 2,3-epoxypropyltrimethylammonium chloride (EPTAC) and polyoxypropylenediamine (Jeffamine D230). Along with excellent inhibition capacity, OPLL also possessed good thermal stability and a broad pH adaptability, and therefore, it can perform well under high temperatures up to 180 °C and in the pH range of 7 to 10. Based upon a combined use of X-ray diffraction (XRD) and zeta potential techniques, the inhibition mechanism was determined. The excellent performance of OPLL on shale can be attributed to the synergistic effects of the inhibition of the MMT crystalline swelling and the weakening of the diffuse double layer repulsion between clay particles. Additionally, biodegradability tests proved that OPLL is an environmentally friendly shale inhibitor that can be readily biodegraded.

Drilling Fluid from Natural Vegetable Gum

Natural vegetable gum drilling fluids with high-temperature resistance are developed for environmental protection. The vegetable gum is chosen as raw material. All agents such as major treatment agent TLJ-1 and auxiliary treatment agents LV-CMC, PEG, and QS-2 are friendly to environment. By changing the physical and chemical environment of the fluid, temperature resistance capability of the fluid is studied. Laboratory tests show the performance of the fluid.

A Study on Oil Sludge Fueling Treatment and Its Mechanism in Field Operations

Oil sludge mainly includes oil sludge from tank (at the bottom of tank), grease trap sediment, wastewater treatment plants residue, remainder of activated sludge remainder, and so on. The treatment and application of oil sludge is essential to environmental protection in oil and gas industry, but it is very hard to solve this problem. The oil sludge contains oil, benzene series, phenols, anthracene, pyrene, and other substances that are stinky and toxic. They are dangerous wastes defined by national laws. On the other hand, oil sludge contains plenty of hydrocarbons, whose potential energy is tremendous and high in calorific value, which is 5,000 kcal/kg on average. The great amount of oil sludge and its special components determine the necessity of recycling and innocuous treatment for the hydrocarbons. Based on lots of experiments, a new oil sludge fueling treatment agent is developed, which is composed of demulsifier, dispersing agent, ignition agent, and catalyst, so it can make the oil sludge break the emulsion quickly. The sludge after dehydration is not adherent and caked for one another. The sludge is easy to burn after drying and burns with coal as well. Both the boiler ash of dry oil sludge and the exhaust gas after burning with coal satisfy relevant emission standard in our country, and do not have influence on environment. Meanwhile, the authors also studied the functional mechanism of oil sludge treatment agent (drying agent) and analyze the effect and mechanism of every component of drying agent acting on oil sludge fueling. Using the oil sludge fueling technology, oil sludge can be processed into powder, and then burned with coal or used as shaped coal directly. This technology not only realizes zero emission of oil sludge required by environmental objectives, but also takes full advantage of the energy contained in residual oil in oil sludge, which realizes reutilization of oil sludge.

Wettability Alteration of Sandstone by Chemical Treatments

Liquid condensation in the reservoir near a wellbore may kill gas production in gas-condensate reservoirs when pressure drops lower than the dew point. It is clear from investigations reported in the literature that gas production could be improved by altering the rock wettability from liquid-wetness to gas-wetness. In this paper, three different fluorosurfactants FG1105, FC911, and FG40 were evaluated for altering the wettability of sandstone rocks from liquid-wetting to gas-wetting using contact angle measurement. The results showed that FG40 provided the best wettability alteration effect with a concentration of 0.3% and FC911 at the concentration of 0.3%.