Downhole Sludge and Deposition - Characterization and Treatment Design

Abstract Sludge formation in oil wells results in near wellbore flow restriction or causes damage to electric submersiable pumps (ESP), thus, reducing their lifetime and causing operational upsets. Prevention and cleanout solutions of such deposits require understanding of sludge characterization and potential formation mechanism. The objective of this study is to present typical types of oilfield sludge and propose a systematic testing protocol to properly characterize organic/inorganic depositions. Examples of typical oilfield sludge deposits were obtained for the study that either organic, inorganic, or mixtures of both. Several experimental and analytical techniques were used to develop a testing protocol for sludge characterization and remediation. This include filtration, centrifugation, extraction, solubility,, acid digestion, and geochemical analysis, pyrolysis, thermogravimetric analysis, Saturates Aromaticss Resin Analysis (SARA) fractions, Gas chromatography–mass spectrometry, thermogravimetric analysis, x-ray diffraction/fluorescence. Solvents were obtained characterize and analyze sludge components such as benzene, toluene, diesel, n-pentane, chloroform, dichloromethane, terpene or naphthalene-based solvents, HCl acids. A sludge characterization workflow and testing protocol was developed that include the following main categories: 1) Sample preparation, 2) phase separation, 3) liquid portion, 4) water portion, 5) organic content, 6) inorganic content, and 7) sludge re-formation. The process provided characterization of the sludge composition and potential forming mechanisms such as inorganic, organic, water content and compositions. Most oilfield sludge deposits are mixtures of organic and inorganic components. Implementing systematic analysis procedures helped to better characterize the sludge samples. For instant SARA analysis showed presence of asphaltene in a sludge sample while Gas Chromotography (GC) and Gas Chromotography Mass Spectrometer (GC-MS) analysis suggested presence of synthetic polymer used in drilling operations of characteristics similar to ashapltene. In another example, treating a sludge sample composed of organic and inorganic components with only diesel, mutual solvent, or naphtha feeds was sufficient to partially dissolve and liquefy the sludge, thus, allowing it to be flowed back during production, and eliminating the risk of using HCl acid in acid-sensitive formations.