Traditional foam hydraulic fracturing fluids used guar cross-linking technology. However, major production problems, such as high friction and difficulty to accurately control the cross-linking time, ...have influenced the large-scale application of cross-linked guar foam fracturing fluids. In this study, we developed a novel non-cross-linked foam fracturing fluid using a series of polymers synthesized with acrylamide and hexadecyl trimethylallyl ammonium chloride as monomers and improved the stability of foam by forming structures in solution through association. The results showed that the hydrophobic groups were the key factors that affect the foam stability, and the hydrolysis degree had a significant effect on the elasticity of the polymer solution. The model association polymer with 0.75% hydrophobic group content and 56% hydrolytic degree was optimal. The stability of our proposed foam was comparable to that of the cross-linked guar gum foam. The adsorption of associating polymers on the gas and water interface resulted in a high-stability foam. Our study demonstrates a new avenue to develop high-stability foams to satisfy the current hydraulic fracturing scheme.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
In the continuous liquid distribution process, the emulsion drag-reducing agent has poor viscosity-increasing ability and a low solid content, resulting in a high concentration and high cost. To ...solve this problem, a nanosuspension agent with a “shelf structure,” a dispersion accelerator, and a density regulator were used as auxiliary agents to realize the stable suspension of a polymer dry powder in an oil phase. The results show that the molecular weight of the synthesized polymer powder could reach nearly 28 million when the mass ratio of acrylamide (AM) to acrylic acid (AA) was 80:20 and a chain extender was added. The synthesized polymer powder was dissolved in tap water and 2% brine separately, and the viscosity of the solutions was measured. The dissolution rate of up to 90% was reached at 30 °C, and the viscosity was 33 and 23 mPa s in tap water and in 2% brine, respectively. A stable suspension can be obtained without obvious stratification in one week and with good dispersion after 6 months by using the following composition: 37% oil phase + 1% nanosuspension agent + 10% dispersion accelerator + 50% polymer dry powder + 2% density regulator. The drag-reduction performance is good, remaining close to 73% with increasing time. The viscosity of the suspension solution is 21 mPa s in 50% standard brine, and the salt resistance is good. The rate at which the suspension fracturing fluid damages the formation is 7.56%, and the reservoir damage is unsubstantial. Its performance in field applications illustrated that its sand-carrying capacity, referring to the capacity of the fracturing fluid to carry proppants into the fracture and place them in a predetermined position, reaches 10%. The results show that the fracturing fluid can be used as a pre-fluid to break the formation, form fractures, and expand fracture networks under low-viscosity conditions and can be used as a sand-carrying fluid to carry proppants into the formation under high-viscosity conditions. Additionally, the fracturing fluid can directly realize the fast conversion between high and low viscosities and allow for multiple uses of one agent.
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Polyacrylamide hydrogel used in conformance control is subjected to poor stability at an elevated temperature. In this paper, nanosilica has been found to be a very effective stabilizing agent for ...the polyacrylamide/polyethylenimine hydrogel, and the reinforcing performance of nanosilica on the hydrogel was investigated in detail. The result showed that the strength of hydrogel is enhanced obviously by the nanosilica, and the hydrogel syneresis is also significantly inhibited by the nanosilica, which can increase the hydrogel stability time from 18 to 180 days at 130 °C. Besides, nanosilica can increase the shear viscosity and hydrodynamic radius of polyacrylamide, and the bound water in the hydrogel is also grown in the presence of nanosilica. In comparison to the micromorphology of common hydrogel, the dense and strong mesh structure is formed as a result of the reinforcing behavior of nanosilica. According to the above results, it is inferred that the silanol group of nanosilica cross-links with the amidogen of polyacrylamide via the hydrogen bond, which is considered as the primary cause of the reinforcing performance of nanosilica for the hydrogel. In addition, as a result of the improving strength and stability and increasing absorption of the polymer to rock surface, the hydrogel enhanced by nanosilica has a higher water shutoff ratio and residual resistance factor and a longer period of validity.
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The hydrophobic associating polymer (MXN‐1) was used as a foam stabilizer with optimized supporting additives to solve the problem of high friction in foam fracturing fluid. The basic formula was ...0.3% MXN‐1 + 0.08% sodium dodecyl sulphate (SDS) + 0.3% B‐14 + 1% potassium chloride (KCl) + 0.03% ammonium persulphate (APS). The friction reduction, sand‐carrying capacity, gel‐breaking performance, and core damage of the fracturing fluid system were studied. The results showed that the proposed system had a unique friction reduction advantage compared with the cross‐linked guar gum foam fracturing fluid, and the friction reduction percent reached 62% at a high flow rate. The surface tension of the gel breaking solution was lower than 25 mN/m, and the residue content was about 7 mg/L.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
The hydrophobic associating polymer (MXN‐1) was used as a foam stabilizer with optimized supporting additives to solve the problem of high friction in foam fracturing fluid. The basic ...formula was 0.3% MXN‐1 + 0.08% sodium dodecyl sulphate (SDS) + 0.3% B‐14 + 1% potassium chloride (KCl) + 0.03% ammonium persulphate (APS). The friction reduction, sand‐carrying capacity, gel‐breaking performance, and core damage of the fracturing fluid system were studied. The results showed that the proposed system had a unique friction reduction advantage compared with the cross‐linked guar gum foam fracturing fluid, and the friction reduction percent reached 62% at a high flow rate. The surface tension of the gel breaking solution was lower than 25 mN/m, and the residue content was about 7 mg/L.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A kind of JDL-1 thickener for betaine hydrophobic association polymer was prepared by aqueous solution polymerization of mixed micelles, AM, AA, AMPS and DM16 were used as raw materials, which was ...synthesized by redox initiator system. Friction tester and high-temperature rheometer were used to evaluate the resistance reduction and temperature and shear resistance of the thickener. The results show that the viscosity average molecular weight of the polymer prepared with AM, AA, AMPS and DM16 mass ratio of 70∶20∶5∶5 was higher than 12 million, and the dissolution time of the polymer was less than 3 min. When the surfactant is used for physical cross-linking, the apparent viscosity of the cross-linked fracturing fluid is larger than that of 60 mPa·s at 90 °C, 170 s-1 sheared 1 h; when metal cross-linking agent is used for coordination cross-linking, the apparent viscosity is larger than that of 80 mPa·s at 120 °C, 170 s-1 sheared 1 h. The drag reduction rate was 73%, the anti-swelling rate was higher than70%, and the damage rate was less than10%. The field trial was successful and confirmed the multifunctional effect of betaine-type hydrophobic associating polymer.
With hydrophobic associating polymer (BCG-1) and anionic surfactant sodium dodecyl benzene sulfonate (SDBS) solution as the object, this work studies the different polymer concentration and ...surfactant concentration on the influence law of fluid properties and examines the sand sedimentation rate and the correlation of fluid properties. After the liquid was tested by electron microscope and rheometer, it was found that the interaction between the surfactant and the polymer is with phases, which provided different angles for revealing the change rule of the deposition rate of sand. When the concentration of SDBS solution is in the second phase (0.05–0.2%), although the system property changes slightly and the microscopic morphology does not change greatly, the deposition rate of sand still decreases significantly. Relaxation time spectrometry explains that the reduction in the sedimentation rate of the sand is caused by the shift of the polymer chain motion mode, whereas the phase angle can clearly manifest this change, and the phase angle is highly correlated with the deposition rate of sand.
The fundamental cause of the proppant suspension behavior in hydraulic fracturing fluids lies in its internal microcosmic network structure and structural strength. In addition to chemical ...crosslinking, another method to form a network structure is established in this paper. Hydrophobically associating polyacrylamide and an anionic surfactant self-assembly process was applied to form a network structure. Compared with crosslinked hydroxypropyl guar gel, the new fracturing fluid even has better proppant suspending properties in static conditions. The capability does not result from crosslinkage but from reinforced physical associations between chains. The performance of this new fracturing fluid was tested and the results showed that it can fully satisfy the requirement of fracturing fluid. Field test shows excellent stimulation effects during its applications in 400 wells in eight oilfields in China.
Generally, a large amount of training data is essential to train deep learning models for obtaining more accurate detection performance in the computer vision domain. However, collecting and ...annotating datasets will lead to extensive costs. In this paper, we propose multi-task network based on multi-scale channel attention to learn general video features without adding any human-annotated labels, aiming at improving the performance of violence recognition. Firstly, we propose a violence recognition method based on a convolutional neural network with the self-supervised auxiliary task, which can learn visual features for improving down-stream task (recognizing violence). Secondly, we establish a balance-weighting scheme to solve the crucial problem of balancing the self-supervised auxiliary task and violence recognition task. Thirdly, we develop a multi-scale channel attention module, indicating that the proper use of the channel attention mechanism can effectively reduce the weights of the feature channels and regions representing the background, further improving the semantically meaningful representation of the network. To evaluate the proposed method, two benchmark datasets have been used, and better performance can be shown by the experimental results compared with other state-of-the-art methods.
The anterior cingulate cortex (ACC) is thought to be important for acute pain perception as well as the development of chronic pain after peripheral nerve injury. Nevertheless, how ACC neurons ...respond to sensory stimulation under chronic pain states is not well understood. Here, we used an
two-photon imaging technique to monitor the activity of individual neurons in the ACC of awake, head restrained mice. Calcium imaging in the dorsal ACC revealed robust somatic activity in layer 5 (L5) pyramidal neurons in response to peripheral noxious stimuli, and the degree of evoked activity was correlated with the intensity of noxious stimulation. Furthermore, the activation of ACC neurons occurred bilaterally upon noxious stimulation to either contralateral or ipsilateral hind paws. Notably, with nerve injury-induced neuropathic pain in one limb, L5 pyramidal neurons in both sides of the ACC showed enhanced activity in the absence or presence of pain stimuli. These results reveal hyperactivity of L5 pyramidal neurons in the bilateral ACC during the development of neuropathic pain.
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