Temporal variations in geochemistry of hydraulic fracturing fluid and flowback water in a tight oil reservoir

Hydraulic fracturing facilitates the development and exploitation of unconventional reservoirs.In this study,the injected hydraulic fracturing fluid(HFF)and flowback and produced water(FPW)in tight oil reservoirs of the Lucaogou Formation in the Junggar Basin are temporally sampled from day 1 to day 64.Freshwater is used for fracturing,and HFF is obtained.The chemical and isotopic parameters(including the water type,total salinity,total dissolved solids(TDS),pH,concentrations of Na^(+),Cl^(-),Ba^(+),K^(+),Fe^(2+)+Fe^(3+),and CO_(3)^(2-),dD,and δ^(18)O)are experimentally obtained,and their variations with time are systematically analyzed based on the flowback water.The results show that the water type,Na/Cl ratio,total salinity,and TDS of the FPW change periodically primarily due to the HFF mixing with formation water,thus causing δD and δ^(18)O to deviate from the meteoric water line of Xinjiang.Because of watererock interaction(WRI),the concentrations of Fe^(2+)+Fe^(3+)and CO_(3)^(2-)of the FPW increase over time,with the solution pH becoming more alkaline.Furthermore,based on the significant changes observed in the geochemistry of the FPW,three separate time intervals of flowback time are identified:Stage Ⅰ(<10 days),where the FPW is dominated by the HFF and the changes in ions and isotopes are mainly caused by the WRI;Stage Ⅱ(10-37 days),where the FPW is dominated by the addition of formation water to the HFF and the WRI is weakened;and finally,Stage Ⅲ(>37 days),where the FPW is dominated by the chemistry of the formation water.The methodology implemented in this study can provide critical support for the source identification of formation water.

Theoretical Model of Dynamic Bulk Modulus for Aerated Hydraulic Fluid

Existing models of bulk modulus for aerated hydraulic fluids primarily focus on the effects of pressure and air fraction,whereas the effect of temperature on bulk modulus is disregarded.Based on the lumped parameter method and the full cavitation model,combined with the improved Henry’s law and the air polytropic course equation,a theoretical model of dynamic bulk modulus for an aerated hydraulic fluid is derived.The effects of system pressure,air fraction,and temperature on bulk modulus are investigated using the controlled variable method.The results show that the dynamic bulk modulus of the aerated hydraulic fluid is inconsistent during the compression process.At the same pressure point,the dynamic bulk modulus during expansion is higher than that during compression.Under the same initial air faction and pressure changing period,a higher temperature results in a lower dynamic bulk modulus.When the pressure is lower,the dynamic bulk modulus of each temperature point is more similar to each other.By comparing the theoretical results with the actual dynamic bulk modulus of the Shell Tellus S ISO32 standard air-containing oil,the goodness-of-fit between the theoretical model and experimental value at three temperatures is 0.9726,0.9732,and 0.9675,which validates the theoretical model.In this study,a calculation model of dynamic bulk modulus that considers temperature factors is proposed.It predicts the dynamic bulk modulus of aerated hydraulic fluids at different temperatures and provides a theoretical basis for improving the analytical model of bulk modulus.

Comparison of Lubricities of Two Novel Benzotriazole Derivatives Used as Additives in Water-Glycol Hydraulic Fluid

Two kinds of benzotriazole derivatives with and without sulfur （abbreviated as BSC and BC, respectively,） were synthesized and their lubricating, anticorrosion and antirust properties were investigated, when they were used as additives in the water-glycol fluid. The morphology and chemical species of typical elements on the worn surface were examined by the scanning electron microscopy （SEM）, the energy dispersive spectrometry （EDS）, and the X-ray photoelectron spectroscopy （XPS） in order to reveal the tribological mechanisms. The results indicated that two synthesized additives could effectively improve the anti-wear, friction-reducing, load-carrying, anticorrosion, and antirnst properties of the base fluid. The surface analysis illustrated that stable nitrogen-containing absorption films generated by BC should be responsible for its facilitated anti-wear and friction-reducing performance, and the excellent lubricities of BSC should be attxibuted to the combined action of adsorption film and tribo-chemical film which were composed of iron oxides, iron sulfides and iron sulfates. The superior lubricating properties of BSC as compared to that of BC demonstrated the effectiveness of elemental sulfur in reducing friction and wear, especially under high loads. But corrosion wear is more obvious at a relative high concentration of elemental sulfur.

Sensitivity assessment of strontium isotope as indicator of polluted groundwater for hydraulic fracturing flowback fluids produced in the Dameigou Shale of Qaidam Basin

Hydrogeochemical processes that would occur in polluted groundwater and aquifer system,may reduce the sensitivity of Sr isotope being the indicator of hydraulic fracturing flowback fluids(HFFF)in groundwater.In this paper,the Dameigou shale gas field in the northern Qaidam Basin was taken as the study area,where the hydrogeochemical processes affecting Sr isotope was analysed.Then,the model for Sr isotope in HFFF-polluted groundwater was constructed to assess the sensitivity of Sr isotope as HFFF indicator.The results show that the dissolution can release little Sr to polluted groundwater and cannot affect the εSr(the deviation of the 87Sr/86Sr ratio)of polluted groundwater.In the meantime,cation exchange can considerably affect Sr composition in the polluted groundwater.The Sr with low εSr is constantly released to groundwater from the solid phase of aquifer media by cation exchange with pollution of Quaternary groundwater by the HFFF and it accounts for 4.6% and 11.0% of Sr in polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater,respectively.However,the Sr from cation exchange has limited impact on Sr isotope in polluted groundwater.Addition of Sr from cation exchange would only cause a 0.2%and 1.2% decrease in εSr of the polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater,respectively.These results demonstrate that hydrogeochemical processes have little effect on the sensitivity of Sr isotope being the HFFF indicator in groundwater of the study area.For the scenario of groundwater pollution by HFFF,when the HFFF accounts for 5%(in volume percentage)of the polluted groundwater,the HFFF can result in detectable shifts of εSr(Δ_(εSr)=0.86)in natural groundwater.Therefore,after consideration of hydrogeochemical processes occurred in aquifer with input of the HFFF,Sr isotope is still a sensitive indicator of the Quaternary groundwater pollution by the HFFF produced in the Dameigou shale of Qaidam Basin.

Uniformity evaluation and optimization of fluid flow characteristics in a seven-strand tundish

The effect of flow control devices（FCDs） on the uniformity of flow characteristics in a seven-strand symmetrical trapezoidal tundish was studied using both an experimental 1：2.5 hydraulic model and a numerical simulation of a 1：1 geometric model.The variation coefficient（CV） was defined to evaluate the flow uniformity of the seven-strand tundish.An optimized FCD configuration was proposed on the basis of the evaluation of experimental results.It is concluded that a turbulence inhibitor（TI） and U-type dam are essential to improve the uniformity of fluid flow in the seven-strand tundish.In addition,the configuration of inclination T-type dams with a height of 200 mm between the second and third strands and with a height of 300 mm between the third and fourth strands can minimize the proportion of dead zone.After optimizing the configuration of FCDs,the variation coefficient reduces below 20%of the mean value,and the average proportion of dead zone is just 14.6%;in addition,the temperature fluctuation between the strands could be controlled within 0.6 K.In summary,the uniformity of flow and temperature in the seven-strand tundish is greatly improved.

Modeling the effects of mechanical parameters on the hydrodynamic behavior of vertical current classifiers

This study modeled the effects of structural and dimensional manipulations on hydrodynamic behavior of a bench vertical current classifier. Computational fluid dynamics （CFD） approach was used as modeling method, and turbulent intensity and fluid velocity were applied as system responses to predict the over- flow cut size variations. These investigations showed that cut size would decrease by increasing diameter and height of the separation column and cone section depth, due to the decrease of turbulent intensity and fluid velocity. As the size of discharge gate increases, the overflow cut-size would decrease due to freely fluid stream out of the column. The overflow cut-size was significantly increased in downward fed classifier compared to that fed by upward fluid stream. In addition, reforming the shape of angular overflow outlet＇s weir into the curved form prevented stream inside returning and consequently unselec- tire cut-size decreasing.

Practical Performance of High Bulk Modulus Oil

Although hydraulic drives have an advantage of high power density, volumetric shrinkage of hydraulic fluids due to pressure causes various disadvantages such as delay of hydraulic response and compression energy loss. Hydraulic fluids of new concept, high bulk modulus oils, have been developed as a new approach to improve the performance of a hydraulic servo system and verified. In this paper, practical performances of high bulk modulus oil, such as oil temperature rise during pump test, air bubbles generation by ultrasonic wave vibration, oxidation stability and anti-wear property, were studied. And the new oil was confirmed to have excellent practical performances besides advantages in pressure response and volumetric efficiency of pumps. Various new applications of the new oil are promising.

Study on a New Technique of On-line Monitoring of Oil Contamination Level Using Computer Vision Technology

In this paper, a new technique of capturing the images of debris inlubrication or hydraulic oil using micro-imaging and computer vision techniques is introduced. Byway of image processing, the size and distribution of debris are obtained, and then the oilcontamination level is also obtained. Because the information of oil contamination is obtaineddirectly from the images of debris by this method, the monitoring result is more intuitive andreliable.

HYDRAULIC PERFORMANCES OF SKIMMING FLOW OVER STEPPED SPILLWAY

Hydraulic performances of skimming flow over stepped spillway was studied by means of hydraulic model experiments. The stepped spillway is a modification of the WES (Water Experiment Station) standard spillway. The experimental results indicated that the stepped spillway is more effective at dissipating energy, the dissipation ratio decreases with increasing discharge, and the free surface air entrainment on stepped spillway occurs much more upstream than on smooth spillway.

Empirical study of gum ghatti as an alternative thickening agent in hydraulic fracturing

Gum ghatti(anogeissus latifolia)is being widely used as an emulsifier,thickener,stabilizer in food,pharmaceutical,and allied industries due to its shelf life,tolerance of heat,and pH stability.Considering the oil&gas industry application,it is ideal for a hydraulic fracturing fluid additive as a direct replacement for guar gum.Basically,unlike guar gum,it contains less residual hull and it is suitable for low permeability unconventional reservoir;mainly shale gas reservoir,where permeability counts trivial in amount.The polymer of ghatti aid exceptional rheological properties and help to produce higher molecular weight polymer;which has excellent proppant carrying capacity and fracture propagation.In this paper,the experimental study has been carried out in two different phases.This was achieved through optimization and characterization of hydraulic fracturing fluid which was embedded with gum matrices.In Phase-I,the study was carried out by using response surface methodology(RSM).Wherein,the relation between several explanatory and response variables have been measured.In Phase-II,the characterization was done by using a scanning electron microscope(SEM),differential scanning calorimeter(DSC),thermo-gravimetric analysis(TGA)and also,Fourier-transform infrared spectroscopy(FTIR).This experimental study will potentially benefit for development of a new hydraulic fracturing fluid.Where gum ghatti observed as a satisfactory alternative agent for guar gum.

Emergence of nanotechnology in the oil and gas industry:Emphasis on the application of silica nanoparticles

The application of nanotechnology in the oil and gas industry is on the rise as evidenced by the number of researches undertaken in the past few years.The quest to develop more game-changing technologies that can address the challenges currently facing the industry has spurred this growth.Several nanoparticles,of different sizes and at different concentrations,have been used in many investigations.In this work,the scope of the study covered the application of nanotechnology in drilling and hydraulic fracturing fluids,oilwell cementing,enhanced oil recovery(which includes transport study,and foam and emulsion stability),corrosion inhibition,logging operations,formation fines control during production,heavy oil viscosity reduction,hydrocarbon detection,methane release from gas hydrates,and drag reduction in porous media.The observed challenges associated with the use of nanoparticles are their stability in a liquid medium and transportability in reservoir rocks.The addition of viscosifier was implemented by researchers to ensure stability,and also,surface-treated nanoparticles have been used to facilitate stability and transportability.For the purpose of achieving better performance or new application,studies on synergistic effects are suggested for investigation in future nanotechnology research.The resulting technology from the synergistic studies may reinforce the current and future nanotechnology applications in the oil and gas industry,especially for high pressure and high temperature(HPHT)applications.To date,majority of the oil and gas industry nanotechnology publications are reports of laboratory experimental work;therefore,more field trials are recommended for further advancement of nanotechnology in this industry.Usually,nanoparticles are expensive;so,it will be cost beneficial to use the lowest nanoparticles concentration possible while still achieving an acceptable level of a desired performance.Hence,optimization studies are also recommended for examination in future nanotechnology research.