查看更多>>摘要：In order to systematically study the rheological and morphological characteristics of foam fracturing fluid, hydroxylpropyl guar (HPG) was selected as the foam stabilizer, sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) were selected as the foaming agents, and foam fracturing fluid used for coalbed methane (CBM) stimulation was prepared. The viscosity, quality and half-life of foam fracturing fluid under different additive concentration levels were tested, and the bubble morphology and its relationship with half-life were observed and quantitatively analyzed with microscopy. In addition, the influence of pulverized coal on foam stability was also studied. The results show that the influence of pulverized coal on the basic parameters of the foam fracturing fluid correlated with the particle size and concentration of the pulverized coal. The small particle size of pulverized coal increased the liquid phase viscosity and half-life of the foam, but reduced the foam quality. With increasing pulverized coal concentration, the effects were enhanced. The average bubble diameter decreased with increasing HPG concentration, and the changing trend of the bubble diameter conformed to the gamma distribution. The foam half-life had a positive and negative correlation with the bubble morphology parameters alpha and beta, respectively. The results can deepen the understanding of the influence of foaming agents, foam stabilizers, and coal particles on the properties of foam fracturing fluids, and provide a reference for the optimization of foam fracturing fluid formulations.
查看更多>>摘要：Determining the appropriate friction factor value for calculating the frictional pressure loss of non-Newtonian fluids in a pipe is a critical task. This study aims to obtain an explicit friction factor correlation to accurately calculate the pressure losses for turbulent flow of yield pseudoplastic fluids in both smooth and rough pipes. A series of experiments are carried out with carboxymethyl cellulose (CMC) solutions using pipes of three different relative roughness. The Herschel-Bulkley model is found to be the most appropriate model to describe the yield pseudoplastic behavior of the CMC solutions used in this study. Based on the experimental friction pressure data obtained from the Izmir Katip C,elebi University flow loop, an explicit correlation is developed here. The new friction factor equation is compared with not only experiments in this study, but also experimental data presented by Okafor and Evers (1992), Subramanian (1995) and Vjargah et al. (2017). Results show that the proposed friction factor correlation is more consistent and better in agreement with experimental data than existing correlations in the literature.
查看更多>>摘要：The formation water evaporates seriously because of the drastic pressure change in near-well zone during the exploitation of deep high temperature gas reservoir. The crystallization salt precipitates in the formation when the salt concentration of formation water increases to solubility limit, which results in the decrease of reservoir porosity and permeability. At present, there is a lack of the prediction and process design of salting out in deep high temperature gas reservoirs. The evaporation salting out experiment of formation water was carried out firstly in this paper, and the volume model of salting out zone was established based on the water content model of natural gas, the porosity and permeability model of reservoir, and the kinetics model of salting out. And the characterization method of predicting porosity and permeability of high temperature gas reservoir after salting out was established by fitting and modifying the model finally, which could provide a theoretical basis for salting out plugging formation in depressurization production of gas reservoirs and laid a foundation for the efficient development of deep high temperature gas reservoirs.
查看更多>>摘要：In this study, the efficacy of blend, of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP), was explored for enhanced CO2 absorption and thereafter, used polymer enhanced carbonated fluid for flow behaviour and oil recovery from synthetic porous media of sand, prepared by wet-ramming of sand in sand-pack. Initially, PVA-PVP blends of varying wt% (2-5 wt% PVA and 1-3 wt% PVP) were formulated and their stability along with potential for CO2 absorption were investigated via viscosity measurements and thermogravimetric analysis over varying pressure, temperature, and saline conditions. Thermal stability results indicated that the performance of PVA-PVP solutions was better (than pure PVA solution) even at 150 degrees C. Comparative viscosity tests indicated that the impact of adverse conditions was least on PVA-PVP solutions consequently, these solutions proved to be excellent CO2 carrier fluid after CO2 solvation experiments in an equilibrium cell. Rheological results indicate strong interactions between PVA and PVP which was understood by the formation of new bonds in solution causing an increase in the viscosity and solid like nature of solution. Finally, these solutions were used as EOR agents for oil recovery from a porous media. The oil recovery tests were performed at a temperature of 40 degrees C and reservoir salinity of 4 wt% NaCl and these results indicated that PVA-PVP solutions displayed enhanced oil mobilization in these conditions. As a result, oil recovery improved by 12-18% original oil in place (OOIP). Thus, based on the results of this study, it can be anticipated that newer polymer composites of PVA-PVP exhibited better synergy with CO2 and act as CO2 carrier fluid for improved oil recovery and enhanced carbon storage. In addition, they are viable candidates for use in elevated temperature and saline conditions of oil reservoirs.
查看更多>>摘要：Mono ethylene glycol (MEG) is highly utilized during gas production to mitigate hydrate formation issue. However, exposing the MEG to reboiler higher temperatures during distillation will lead to the reduced hydrate inhibition performance of the MEG due to thermal degradation and accumulation of organic acids such as glycolic, acetic and formic acids. The hydrate inhibition performance of the thermally degraded MEG was measured isobarically for pure methane gas using a cryogenic sapphire cell for the pressure ranges of 5500 to 20500 kPa. The objective is to determine and optimize the thermodynamic hydrate inhibition performance of thermally degraded MEG influenced by reboiler operation and MEG concentration in the lean MEG product. This research determines that operating the reboiler at high MEG concentration of 80.8 vol % for longer durations of 6.0 h raises the dissociation temperature by an average of 1.4 degrees C compared to 0.9 degrees C for the lower MEG concentration of 40.2 vol % for similar duration of 6.0 h. This suggests that lower MEG concentration will yield lower dissociation temperatures at the same retention time. Hence, the MEG thermodynamic inhibition performance is optimal at lower MEG concentration which results in lower dissociation temperature.
查看更多>>摘要：The three-stage acid fracturing technology is an effective technology for tight sandstone reservoirs with undeveloped natural fractures. Its filed test has achieved good results in the tight sandstone field test in the Daning block of China. The core of this technology is to complete the pump injection procedure of "conventional fracturing, acid fracturing and conventional fracturing" in sequence. However, fracture propagation behaviors vary greatly under different acidizing fracturing conditions. In this paper, the influence of different factors on the uneven degree of hydraulic fracture etching and fracture propagation was studied by triaxial hydraulic fracturing physical simulation experiment. The effects of different acid concentration, acid dosage and acid reaction time on fracture propagation behaviors were analyzed. The results show that the fractures formed by the fracturing with displacement of 160 mL/min in the laboratory did not penetrate the overburden and underburden, and longer fractures and small branch fractures were formed in the reservoir. Hydraulic fractures showed a trend of continuous expansion in the sandstone reservoir, indicating that the fracturing effect was favorable. The experimental displacement is converted to the field displacement of 8 m(3)/min. The influence degree of acid concentration, acid dosage, acid reaction time on fracture propagation of three-stage acidizing fracture decreases in turn. Acid concentration and acid dosage are positively correlated with the area of fracture propagation. The influence of acid injection reaction time on fracture propagation is the lowest, and the influence of acid injection reaction time on fracture propagation area is significant only in the case of high acid dosage or high acid concentration. The influence of acid immersion time on fracture permeability is far less than that of acid concentration on fracture permeability. However, the greater the acid concentration, the greater the impact of acid immersion time on fracture permeability. The experimental results can provide empirical reference for the onsite construction of the three-stage acid fracturing in tight sandstone reservoirs.
查看更多>>摘要：Flow through porous media depends strongly on the spatial distribution of the geological heterogeneities which appear on all length scales. We lack precise information about heterogeneity distribution on various scales, from pore level to reservoir scale. However, some sources provide suitable information. At pore scale, for example, the micro-CT images show considerable insights into pore space structures and play valuable role in porous media characterization. The consequence of all geological heterogeneities is a great deal of uncertainty in dynamic performance of porous media which can be investigated using percolation theory. The main percolation quantities include the connected pore fraction; P, the backbone fraction; B, the dangling ends fraction; D, and the effective permeability; K-eff. By finite size scaling within percolation theory, these quantities (i.e. P, B, D, K-eff) become some functions of total pore fraction; p, and the system dimensionless length; L. In this work we examine the functional forms of percolation quantities on two-dimensional micro-CT images and develop new correlations for such quantities in three-dimensions. The results show good agreement on micro-CT samples with different pore size distribution and wide level of connectivity.
查看更多>>摘要：Aiming at the problem of the unclear microscopic interaction mechanisms between carbon dioxide (CO2) and reservoir rocks and fluids during CO2 huff-n-puff in ultra-heavy oil reservoirs. In this study, scanning electron microscope (SEM) and visual displacement experiment were used to understand the mechanisms among them. Then, the interaction experiment and numerical simulation between CO2 and heavy oil were carried out to verify the feasibility of CO2 huff-n-puff to improve the recovery of ultra-heavy oil reservoirs. The results showed that: a) Within a certain range of pressure, the corrosion ability of carbonated water formed by CO2 and formation water gradually increased as pressure increased. When the pressure increased from 6 MPa to 12 MPa, the average corrosion rate increased from 0.36% to 0.49%. b) CO2 can effectively improve the pore structure and permeability of rocks. The injection of CO2 caused hydration expansion, surface particle peeled off, deepening of depression, the appearance of corrosion pits and cracks, and cracks extending as pressure increased. Under the pressure of 6 MPa and 12 MPa, the permeability increased by 14.67% and 41.86%, respectively. c) CO2 injection made the heavy oil form amount of dispersed secondary foam oil, which greatly reduced the viscosity of crude oil and increased the expansion ability of heavy oil. When the pressure increased to 12 MPa, the volume coefficient and viscosity reduction rate reached 1.18 and 99.62%. d) The displacement experiment demonstrated that the displacement efficiency of CO2 was 23.09% higher than water flooding. e) According to the results of numerical simulation, during five cycles of CO2 huff-n-puff, the reservoir pressure rose from 3481 KPa at the end of depletion production to 6187 KPa, which showed that pressure was effectively maintained; The viscosity of the heavy oil decreased from 12825cp to 3280.49cp, and the 10-year recovery factor was 13.08%. The understanding of the micro-action mechanism could have certain guiding significance for improving the development effect of CO2 huff-n-puff in the ultra-heavy oil reservoirs.
查看更多>>摘要：The deep exploitation of silty reservoirs which store large scales of natural gas hydrate using the replacement method is of great significance for meeting the clean energy demand and reducing carbon emissions. Investigating the effects of CH4-CO2 replacement on the strength and deformation properties of hydrate-bearing silty sediments (HBSSs) plays a vital role in assessing the possible risks and conducting corresponding designs of the silty reservoirs during natural gas production. For that reason, this paper designs a series of CH4-CO2 replacement experiments on the HBSSs followed by the shear tests, and the deformation and strength behaviors of this material during the replacement were obtained and analyzed. The results show that HBSSs presents final compression behaviors after CH4-CO2 replacement while the dilation behaviors could appear due to CH4 hydrate dissociation at the initial stage of replacement. The replacement reduces the Elastic modulus but causes less change on the peak strength and deformation behaviors of CH4 HBSSs. This material also shows the relatively similar stress-dilatancy behaviors before and after partial replacement. The key influence of CH4-CO2 replacement on silty reservoirs may be located in the deformation of HBSSs during the replacement and the Elastic modulus reduction after replacement. These results in this study are wished to provide potential theoretical support for predicting the geo-mechanical response of silty reservoirs if hydrate production is applied using the CH4-CO2 replacement method.
查看更多>>摘要：To avoid premature operational failure of the ESP systems, their vibration levels must be evaluated for acceptance before installation. The vibration assessment of Electrical Submersible Pump (ESP) systems and other rotating machines considers that the most important amplitude occurs in the radial orientation. Typical vibration amplitude estimation uses radial orthogonal sensors and considers the maximum vibration amplitude between the two sensor signals. However, this approach does not account for the orbit's shape, leading to an error up to 41,4% between the maximum estimated amplitude in each sensor and the maximum radial vibration amplitude, the orbit semi-major axis. This paper proposes a method to generate a frequency spectrum with invariance to the shape of the vibration orbit, namely the Orbit Semi-major Axis Spectrum. The proposed method is compared to the typical vibration amplitude estimation approach using individual sensor signals and the Full Spectrum method. The methods are applied on vibration signals from two pumps at different wear states, and results are analyzed. The estimation error of the vibration amplitude in ESP systems due to disregarding the shape of the vibration orbits is shown. The results indicate that the proposed method presented the maximum radial vibration amplitudes of each orbit frequency component (orbit semi-major axis), which is not directly possible with the Full Spectrum and is impossible with the individual frequency spectrum. The orbit semi-major axis amplitudes of the pumps were up to 28% higher than the maximum amplitude estimated from the individual orthogonal sensors.
NSTL
Elsevier