Zhou Zhu

Stability, rheological property and oil-displacement mechanism of a dispersed low-elastic microsphere system for enhanced oil recovery

A dispersed low-elastic microsphere system, consisting of low-viscoelastic microspheres and polymers, is a novel suspension system for enhanced oil recovery in heterogeneous reservoirs. In this study, experiments were performed to characterize the morphology, viscoelasticity, and swelling performance of the synthetic low-elastic microspheres. The stability and rheological property of the dispersed low-elastic microsphere system was investigated using a Turbiscan Lab Expert stability analyzer and an MCR301 rheometer. In the flow and displacement experiments, the parallel-sandpacks model and microscopic visualization models were used to study the oil-displacement effect and micromigration mechanism of the low-elastic microspheres. The experimental results showed that the storage modulus (G′) of the synthetic low-elastic microspheres was only 23.6 Pa and they also had a good swelling property in the simulated formation water. The parallel-sandpacks test and micromodel test indicated that the dispersed low-elastic microsphere system was a promising agent for both conformance control and improved oil recovery in heterogeneous reservoirs. Moreover, the low-elastic microspheres had good deformation and shear resistance performances. Five transport behaviors, such as deformable passing through, partition passing through, blockage, adhesion, and directly passing through, of low-elastic microspheres in a porous medium have been put forward. This study not only provides an understanding of the properties of the dispersed low-elastic microsphere system but also supplies theoretical support for the mechanism of improving oil recovery for the dispersed low-elastic microsphere system.

pH-Responsive wormlike micelles based on microstructural transition in a C22-tailed cationic surfactant–aromatic dibasic acid system

pH-Responsive wormlike micelles based on microstructural transition, and formed by complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and potassium phthalic acid (PPA) at a molar ratio of 2 : 1, were developed and compared with CTAB/PPA at the same molar ratio. Phase behavior, viscoelasticity, and microstructural transitions of solutions were investigated by observing their appearance, rheological characteristics, dynamic light scattering, and 1H NMR measurements. It was found that the phase behavior of UC22AMPM/PPA solutions undergoes transitions from transparent viscoelastic fluid to phase separation with white floaters upon increasing pH. By increasing pH from 2.01 to 6.19, the viscosity of wormlike micelles in the transparent solutions continuously increased and reached ∼1.4 × 106 mPa s at pH 6.19. As pH was adjusted to 7.32, the opalescent solution showed a water-like flowing behaviour and the η0 rapidly declined to ∼1.7 mPa s. The viscosity of the CTAB/PPA solutions had a maximum at pH 2.98 and then decreased with increasing pH. This radical variation in rheological behavior is attributed to the pH dependent hydrophobicity of PPA and ultra-long hydrophobic chain of UC22AMPM. Additionally, dramatic viscosity changes of about 6 magnitudes can be triggered by varying pH without any deterioration for the UC22AMPM/PPA system.

Study on salt thickening mechanism of the amphiphilic polymer with betaine zwitterionic group by β-cyclodextrin inclusion method

A method based on host-guest inclusion system was used to investigate the salt thickening mechanism of poly [acrylamide-co-N, N′-dimethyl (methylmethacryloyl ethyl) ammonium propane sulfonate-co-cetyl dimethyl allyl ammonium chloride] (PADC). The salt thickening behavior of PADC solution was studied by rotational viscometer, and its average hydrodynamic diameter (Dh) was characterized by dynamic light scattering (DLS). The formed host (β-cyclodextrin)-guest (hydrophobic groups of PADC) inclusion system was confirmed by scanning electron microscopy (SEM). A method of characterizing the hydrophobic association strength and determining the hydrophobic association contribution rate (HACR) was introduced by the inclusion of β-cyclodextrin (β-CD). The results showed that the apparent viscosity and the Dh of PADC solution increased with the increase of salt concentration. In addition, the types of salt also affected the thickening property of PADC solution. Moreover, the results of HACR indicated that the hydrophobic association strength of PADC solution was enhanced in the presence of salts, which was confirmed by fluorescent method. Thus, it could be concluded that the salt thickening of PADC solution was caused by the destruction of ionic bonds in betaine monomer and the enhancement of hydrophobic association strength.

Research and Application on Resource Utilization Technology of Oily Waste Drilling Fluid

Abstract Oily waste drilling fluid is divided into two main types, oil based and oil mixed; each is included in the national list of hazardous waste because they contain oil, heavy metals, organic matter, and other pollutants. At present, waste drilling fluid is usually stored centrally or tightly closed all over the world, In this way, the pollutants are only sealed and isolated from the external environment but not completely eliminated and pose the risk of polluting the environment. Furthermore, re-injection into a formation or a landfill cannot recover the mineral oil and recycle the waste resources. This article proposes a technology of utilizing waste oily drilling fluid based on many tests and treatment options screening. The technology is chemical reaction-enhanced separation and hazard-free treatment. The obtained cleaner and the hazard-free treatment agent are added in the waste oily drilling fluid to recover the useful oil and make the remaining sludge less hazardous. The processed waste can be utilized to build cofferdam in the well site. The oil recovery ratio can be up to 85%. The compressive strength is moderate after addition of a hazard-free treatment agent. The product neither hardens soil nor affects the growth of plants; the oil, chemical oxygen demand (COD), heavy metals, and other pollutants in the leaching solution are lower than the second-level criterion in the Integrated Wastewater Emission Standard (GB8978-1996).

Effect of Hydrophobic Association and Polymer Concentration on Viscoelasticity of Amphiphilic Polymer

The viscoelasticity of the polymer for flooding affects the oil displacement efficiency, and the polymer with viscoelastic properties can increase the oil recovery. In this study, the effect of hydrophobic association on the viscoelasticity of the amphiphilic polymer was investigated by rheometer. The critical association concentration (CAC) of the amphiphilic polymer was determined by the relationship curve between zero shear viscosity and polymer concentration, which is about 800 mg/L. With the increasing of amphiphilic polymer concentration, its viscoelasticity exhibits different characteristics and can be converted from a viscous fluid to an elastomeric fluid. The influence mechanism of hydrophobic association on viscoelasticity of amphiphilic polymer was studied by cohesive energy and scanning electron microscope (SEM). The cohesive energy of the amphiphilic polymer increased from 1.26 × 10−4 Pa to 9.25 × 10−2 Pa when the amphiphilic polymer concentration ranged from 500 to 1200 mg/L. Larger supra-molecular aggregates and stronger network structures can be formed when the amphiphilic polymer concentration is higher than the CAC. The results show that the viscoelasticity of amphiphilic polymer is related to the concentration of amphiphilic polymer and the association strength. This study has certain guiding significance for the application of amphiphilic polymer in oil and gas field development.

Effect of different molecular weight amphiphilic polymers on emulsifying behavior

Abstract Amphiphilic polymers applied in oil fields are polymer mixtures with different molecular weight. Stability of O/W emulsion prepared by amphiphilic polymers with different molecular weight was studied by stability analyzer. The difference in stability was clarified according to the external phase and interfacial properties. Results showed that PI(micro-molecular polymer) formed a tighter network structure in solution which exhibit higher viscoelasticity and more resistant to shear; and was more favorable to the emulsion stability than PII(macro-molecular polymer) due to higher surface activity. This work provides references for the molecular weight distribution optimization of amphiphilic polymer.

Gel kinetic characteristics and creep behavior of polymer microspheres based on bulk gel

Abstract Deep profile control technology of polymer microspheres has become a widely used new method in improving oil recovery in heterogeneous reservoirs. The viscoelastic property of polymer microspheres plays an important role in the deformable migration behavior. In this study, a new method of measuring the viscoelastic properties of polymer microspheres based on bulk gel was proposed. Using mechanical rheometer and microrheometer, the effects on the storage modulus and gel performance were systematically researched. The creep-recovery test was applied to characterize the creep behavior of different polymer microsphere bulk gel. The results show that the storage modulus of polymer microspheres could be controlled by adjusting the agent concentration in the synthetic reaction. Moreover, the kinetic equation of gel time of polymer microspheres bulk gel and reaction temperature was established: ln(GT) = 3289.18(1/T)-9.33. Elastic strain index was put forward as a new parameter to characterize the viscoelasticity of polymer microsphere in creep-recovery test. Finally, relationship between elastic strain index and storage modulus was constructed and a classification criterion of polymer microspheres with different viscoelasticity was proposed based on a large number of creep-recovery results. The research could provide a good theoretical guidance and technical support for the understanding of viscoelasticity of polymer microspheres. Graphical Abstract

Study on a Surface Gas-Removing System for Weight Drilling Fluid

Abstract A gravitational separator is often used to remove gas in contaminated drilling fluid during conventional drilling but fails to meet the gas-removing need for weight drilling fluid and to maintain the stable property of fluid by high viscosity for high-pressure gas formation. Therefore, it is essential to research the surface gas-removal system. According to the existing gravitational separator and centrifugal separator structure, computational fluid dynamics (CFD) simulation technology is applied to show the flowfield characteristics of a gravitational separator and centrifugal separator, and a numerical simulation scheme was designed using an orthogonal design method. Range analysis and variance analysis were used to determine the independent factors, such as air bubble diameter and fluid viscosity. Then, based on the numerical simulation results under the separator structure and working condition, the laboratory simulation platform was designed. By comparing numerical calculation with in-house laboratory investigation, the results show that the calculated change tendency of gas-removal efficiency is in agreement with the obtained result from by laboratorial tests on the whole. The design of a double-stage gas-removal system is preferable to dealing with the gas-contaminated weight drilling fluid, which can remarkably raise the gas-removal efficiency. Under laboratory conditions, the double-stage gas-removal system obtained a maximal amplitude beyond 15% compared with the one-stage system, and the separated density was close to the unaerated density. Numerical simulation was helpful for optimizing the structure and determining the best working conditions.