Influence of Polar Pressure Transmission Medium on the Pressure Coefficient of Excitonic Interband Transitions in Monolayer WSe_2

The influence of the pressure transmission medium（PTM）on the excitonic interband transitions in monolayer tungsten diselenide（WSe2）is investigated using photoluminescence（PL）spectra under hydrostatic pressure up to 5GPa.Three kinds of PTMs,condensed argon（Ar）,1：1 n-pentane and isopentane mixture（PM）,and4：1 methanol and ethanol mixture（MEM,a PTM with polarity）,are used.It is found that when either Ar or PM is used as the PTM,the PL peak of exciton related to the direct K-K interband transition shows a pressure-induced blue-shift at a rate of 32±4 or 32±1 meV/GPa,while it turns to be 50±9meV/GPa when MEM is used as the PTM.The indirect A-K interband transition presents almost no shift with increasing pressure up to approximatel.y 5 GPa when Ar and PM are used as the PTM,while it shows a red-shift at the rate of-17±7meV/GPa by using MEM as the PTM.These results reveal that the optical interband transitions of monolayer WSe2 are very sensitive to the polarity of the PTM.The anomalous pressure coefficient obtained using the polar PTM of MEM is ascribed to the existence of hydrogen-like bonds between hydroxyl in MEM and Se atoms under hydrostatic pressure.

Cause analysis and solutions of water blocking damage in cracked/non-cracked tight sandstone gas reservoirs

After hydraulic fracturing treatment,a reduction in permeability caused by the invasion of fracturing fluids is an inevitable problem,which is called water blocking damage.Therefore,it is important to mitigate and eliminate water blocking damage to improve the flow capacities of formation fluids and flowback rates of the fracturing fluid.However,the steady-state core flow method cannot quickly and accurately evaluate the effects of chemical agents in enhancing the fluid flow capacities in tight reservoirs.This paper introduces a time-saving and accurate method,pressure transmission test(PTT),which can quickly and quantitatively evaluate the liquid flow capacities and gas-drive flowback rates of a new nanoemulsion.Furthermore,scanning electron microscopy(SEM)was used to analyze the damage mechanism of different fluids and the adsorption of chemical agents on the rock surface.Parallel core flow experiments were used to evaluate the effects of the nanoemulsion on enhancing flowback rates in heterogeneous tight reservoirs.Experimental results show that the water blocking damage mechanisms differ in matrices and fractures.The main channels for gas channeling are fractures in cracked cores and pores in non-cracked cores.Cracked cores suffer less damage from water blocking than non-cracked cores,but have a lower potential to reduce water saturation.The PTT and SEM results show that the permeability reduction in tight sandstones caused by invasion of external fluids can be list as guar gum fracturing fluid>slickwater>brine.Parallel core flow experiments show that for low-permeability heterogenous s andstone reservoirs with a certain permeability ratio,the nanoemulsion can not only reduce reverse gas channeling degree,but also increase the flowback rate of the fracturing fluid.The nanoemulsion system provides a new solution to mitigate and eliminate water blocking damage caused by fracturing fluids in tight sandstone gas reservoirs.

Integrated feasibility analysis of shale inhibition property by utilization of pore pressure transmission equipment

Regarding the widespread utilization of formate-based drilling fluids in numerous operational circumstances,petroleum industries are in urgent need of decreasing wellbore inefficiencies by improving the procedures quality.Thereby,providing appropriate parameters such as safety,boosting the drilling speed and enrolling the proper procedure of optimizing performances of high activity water-sensitivity formation should be taken into consideration.The objective of this comprehensive study is to apply experimental evaluation tests on the shale inhibitor fluids by using prepared plug samples from the studied field due to the administration of pore pressure transmission(henceforth,PPT)equipment.Even though,PPT equipment is not able to simulate all the mechanisms which are applied to different drilling fluids on the shale layers’stability,it will control such parameters like the penetration of fluid filtration through the formation that subsequently reduce the wellbore problems.Consequently,the ubiquitous use formate fluid in drilling operations of exploratory oil wells in the studied field is successfully implemented to be addressed the current well inefficiencies adequately.