Disposition of Wastewater from Oil Wells in Venezuelan Savannahs and Their Effects on Percolation Waters

Abstract

In the eastern Venezuelan Llanos, the drilling fluids composed of wastewater (WW), accompanying hydrocarbons and wastes from oil activity are deposited in a system of waterproofed pits. Later, by means of siphons, the hydrocarbon phase of the WW is separated. WW are typically very salty and contain suspended and dissolved solids, residual hydrocarbons, and chemicals used in hydrocarbon extraction. So they are transported to a pit and treated with a flocculating agent and lime. Once carried out, the flocculation-coagulation operation and pH correction, WW are released to the environment. The savannas where the treated water are irrigated, in addition to the oil operation, present an intense agricultural and livestock activity, and rest on aquifers that are partially replenished with the percolation waters near the treatment pits. Therefore, this research will aim to analyze: i) the levels of soluble salts and heavy metals in the percolation waters collected in lysimeters located in savanna soils adjacent to oil wells after irrigation with WW treated with flocculating agents, and ii) the estimation of time which these salts take to be dislodged from the soil. The waters from the lysimeters did not report high levels of soluble aluminum or heavy metals since their soluble forms were precipitated by liming. Likewise, the coagulation-flocculation process removed the high levels of barium from the untreated WW. The contributions of sodium and calcium from the WW have a liming effect on the acidity of these soils. The sodium levels contributed by the WW could represent an environmental risk, fortunately, the good internal drainage of these sandy Ultisols allows their removal. Studies with lysimeters showed that the percolation waters of areas irrigated with flocculated water have a similar sodium content to that of control lysimeters six months after treatment.