Experimental Study On Flocculation And Solidification Treatment Of Waste Drilling Mud

The main energy source in the today’s world is oil and gas.It is a basic industry that concerns national economic and social development.As a major oil and gas user,China’s oil and gas production has been increasing in recent years,followed by the production of a large number of waste drilling mud.The composition of waste mud is complex and there are many pollutants.How to avoid its adverse impact on the ecological environment and people’s production and life and achieve harmless treatment is an urgent problem to be solved.This paper takes the waste mud produced in a coalbed methane drilling operation in Shanxi Province as the research object.According to the properties of the waste drilling mud,through the chemical solid-liquid separation,namely gel-breaking and coagulation aid method,and taking the separated liquid phase pollutant content and the water content of the mud cake as the main indexes to explore the gel-breaking effects of three gel breakers,including ferric chloride（FeCl₃）,polymeric aluminum chloride（PAC）and aluminum sulfate（Al₂（SO₄）₃）.On the basis of this,three organic coagulants such as cationic polyacrylamide（CPAM）,anionic polyacrylamide（APAM）and nonionic polyacrylamide（NPAM）are used for collaborative treatment to investigate the coagulation effects of different additions on mud,so that the best combination of gel-breaking coagulant aid is selected.Through the orthogonal test,the process conditions（stirring speed,stirring time and standing time）for the best solid-liquid separation effect of the mud under this combination are obtained.And the pH of the separated liquid phase is adjusted to achieve its harmless treatment.Further,the micro morphology of the original mud sample and the separated mud cake is analyzed by scanning electron microscope（SEM）,and then the gel-breaking and coagulation aid mechanism is explored.The separated mud cake is cured with selfmade slag-based curing agent.The harmless treatment effects of slag-based curing agent is evaluated with the compressive strength of solidified block and the pollutant contents of leaching solution as the index.To compare with 25% cement,the curing performance of slag-based curing agent is investigated.The crystal phase and micro morphology of mud cake before and after curing are analyzed by X-ray diffraction（XRD）and SEM,then explore the curing mechanism.Through the above research,the main conclusions were as follows:（1）For this waste drilling mud,Al₂（SO₄）₃ has the best gel-breaking treatment effect,and its optimal dosage is 2000 mg·L^-1.The treated liquid phase COD_cr,suspended solids concentration,and chromaticity are reduced to 105.31mg·L^-1,38.50 mg·L^-1,and 40 times,and the removal rates are 96.27%,92.25%,and 92.00%,respectively,and the water content of mud cake is 84.46%,petroleum and total chromium content are 1.15 mg·L^-1 and 0.012 mg·L^-1 respectively.（2）The best organic coagulant with Al₂（SO₄）₃ synergistic treatment effect is NPAM,whose optimal dosage is 10mg·L^-1,and the treated liquid phase COD_cr,suspended solids concentration,sludge cake water content and chromaticity are reduced to 61.98 mg·L^-1,32.50 mg·L^-1,78.64% and 20 times respectively,the content of petroleum and total chromium decreased slightly,which are 1.06 mg·L^-1 and 0.01 mg·L^-1 respectively.（3）Under the optimal combination of gel-breaking and coagulant aid,the optimal process conditions for the waste drilling mud in the chamber were obtained by three-factor four-level orthogonal test with the mixing speed of 90 r·min-1,mixing time of 60 s and standing time of 5 min.The treated liquid phase COD_cr,suspended solids content,chromaticity and mud cake moisture content are 38.45 mg·L^-1,30.50 mg·L^-1,20 times and 76.53% respectively,and the petroleum and total chromium contents are 1.05 mg·L^-1 and 0.01 mg·L^-1 respectively.When 5% NaOH of 0.8 mL is added to adjust the pH to 6.07,all indexes measure in liquid phase meet the national level I emission requirements of GB 8978-1996,and harmless treatment is realized.（4）The SEM study found that: the use of the gel-breaking flocculant Al₂（SO₄）₃ and the organic coagulant NPAM can play their respective advantages,and the electric neutralization of the gel-breaking agent and the bridge network trapping of the coagulant can significantly accelerate the flocculation and sedimentation of the particles in the slurry and reduce the water content of the sludge cake and the content of pollutants.（5）When the waste mud cake is treated with slag-based curing agent,it is found that the curing effect is good.The compressive strength of the solidified block with 25% content after curing for 28 days reaches the maximum of 0.64 MPa,and the minimum values of COD_cr,chroma and suspended solids concentration of the leaching solution are 53.26 mg·L^-1,10 times and 37.80 mg·L^-1 respectively.The pH of the leaching solution in each content and curing period are within the specification requirements,the content of total chromium and petroleum in leaching is very low and can not even be detected.Slag-based curing agent can achieve the purpose of "treating waste with waste" and harmless treatment of waste drilling mud cake.（6）When using cement as a comparison test,the compressive strength of cement solidified block is lower than that of slag-based curing agent,and the difference between the two increases with the increase of age.The leaching chromaticity is higher after curing for 3 days,the content of leaching COD_cr and suspended solids are higher than that of slag-based solidified block at the same age,and the leaching pH in each curing period exceeds the standard limit,the results show that slag-based curing agent has better curing performance for mud cake than cement,and reduces the amount of cement,which can reduce the curing cost of waste drilling mud.（7）XRD and SEM tests on the cured body of the mud cake found that: the slag-based curing agent generates a large number of gelling products after hydration reactions,and these gelling substances lap each other to wrap the solid particles and fill the internal pores of the mud cake,thus improving the strength of the cured block and the ability to fix contaminants,and reduce the leaching of pollutants,while the early formation of cement curing block AFt will continue to expand,destroying its internal structure and increasing the pore space,thus reducing the strength of the cement curing block and the ability to fix pollutants,resulting in a decrease in cement curing effect.