Formation damage resulting from organic and inorganic depositions, such as calcium carbonate, asphaltene and paraffin, is one of the most commonly encountered types of damage in the oil and gas industry. These depositions are usually associated with a decrease in crude productivity, accelerated failure of production completions, such as from electric submersible pumps (ESPs), and less footage coverage while running with production and flow profile logging tools. The major concern highlighted is the increased probability of having more organic deposits in the wellbore as a result of the increased scale of the inorganic deposits.

A thick, heterogeneous sludge mix of hydrocarbons and solid materials is a critical subject for characterization and solubility measurements. Analyzed deposit samples were collected either while running with production logging tools, when pulling out a failed ESP, or when lowering the completion equipment. The hydrocarbon phase was removed by organic solvent and the precipitated solid materials were collected for a lab analysis and solubility test. The solid phase analyses included X-ray diffraction (XRD) analysis and scanning/transmission electron microscopy (SEM and TEM). The composition of organic deposit samples was investigated using saturates, aromatics, resins, and asphaltenes (SARA) characterization, Fourier transform infrared analysis (FTIR) and Fourier transform ion cyclotron resonance mass spectrometry (FTMS). The sludge sample solubility tests were conducted over a variety of organic solvents at different temperatures, up to 300°F with a solid mass/liquid volume ratio of 1:10.

The paper presents a typical analysis procedure of organic deposits collected from downhole equipment. The XRD analysis of solid debris materials (inorganic) present in collected sticky materials samples showed that the materials contained mainly carbonate compounds; for instance, calcite-CaCO3, dolomite-CaMg(CO3)2, and Halite-NaCl. These materials were completely soluble in acids like 15 wt% of HCl at reservoir conditions. Calcite scale would have been a problem in cases where the calcium content exceeded 12,000 mg/L. Low solubility results were obtained with static reaction of organic solvents recipes with the sticky materials around 17 to 50 wt%. This, in turn, increased solubility up to 98% as observed from the reaction in dynamic conditions.

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