The Experimental Investigation Of Drilling Waste Slurries Solidification With Phosphogypsum And Cinder Ash

The drilling waste slurries are the main pollutants produced in oil & Gas drilling fields. They have the water quality characteristics of changeability and complexity of component. Usually their COD_Cr content, pH value and chroma are higher than those regulated in standard. They contain some oil component. Due to specialties of drilling operation they are dispersing and movability, too. According to the characteristics of drilling waste slurries, experimental studies on solidification treatment with various drilling waste slurries samples with composite solidification agent composed of phosphogypsum, cement, quicklime, and water-reducing agent etc., have been made. Effects of all kinds of factors on drilling waste slurries solidification results have been investigated. The mechanism of solidifying treatment has been studied, too. Experimental results: (1) After many experiments studying, the main solidification raw materials and their fitting ranges of the dosage are brought forward: i.e., cement 10¹5%, cinder ash 7¹0%, phosphogypsum 3⁵%, quicklime 1²%. The solidification agent can immobilize the drilling waste slurries effectively. The mechanic strength of compressing resistance of the formed concretion can reach 2.6MPa, and the porous structures of the concretion present certain adsorption abilities. The leaching tests indicate that the contamination contents of lixivium are lower than that allowed by the Standard Code(GB 8978-1996) for oil drilling wastewater. (2) The characteristics of the drilling waste slurries affect the solidification strongly. The water-based drilling waste slurries can be disposed comparatively easily. The changes of solids content (or density) affect the solidifying effects evidently. When the water-based drilling waste slurries with high solids content (or their density >1.5 g/cm3) are disposed in the case of the proportion of cement dosage in the solidification agent of approximate 10%, the contamination contents of lixivium can accord with the Standard Code(GB 8978-1996) for oil drilling wastewater. When the proportion of cement dosage is 13% the compressing resistances of the formed concretion can exceed 2.0MPa. The oil-based drilling waste slurries have great toxicity and cannot be disposed easily. Only when the proportion of cement dosage of the solidification agent for the slurries solidification is higher than 15% the contamination contents of lixivium can accord with the Standard Code(GB 8978-1996). Therefore, to obtain good solidifying effects the oil-based drilling waste should firstly be pretreated by a series of processes, i.e., acidification and neutralization, or demulsification and removing oil, or coagulation and removing water etc., before they are disposed with solidification methods. (3) The contrast experiments of solidification with phosphogypsum and gypsum indicate that phosphogypsum may substitute for gypsum to solidifying the drilling waste slurries under the condition of phosphogysum being activated with calcium oxide and cement. Moreover, its negative effects of deleterious impurities can be eliminated during the solidifying process; hence, no secondary pollution can be formed. (4) The cinder ash has strong adsorption capabilities besides having the activation of pozzolana and actively hydrating with phosphogysum and cement. The deleterious substances among the drilling waste slurries can be immobilized in the concretion by physical adsorption function. (5) The use of organic solidification agent (macromolecule polymer) can enhance the compressing resistances and tenacity of the formed concretions. It can, however, increase the CODCr value of the concretion leaching liquor. Hence, it may result in the secondary pollution.The composite solidification agent composed of phosphogysum and cinder ash can effectively dispose of the water-based (or oil-based) drilling waste slurries by solidification method. The slurries can be disposed and their negative effects of the deleterious substances can be eliminated. It demonstrates a promising application for phosphogypsum and cinder ashes in wastewater treatment in oil drilling industry. Aimed at the characteristics of high oil content and difficult treatment with solidification method of the oil-based drilling waste slurries, the elementary incinerating process and the process design of main equipments were done, which offers certain foundation for the follow-up work of ulteriorly consummating the effective disposals of the drilling waste slurries on drilling scene.