Heavy organic deposit comprehensive analysis and testing techniques

Abstract

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 equipment, such as electrical submersible pumps (ESPs), and less footage covered while running with production and flow profile logging tools. Therefore, formation damage and in particular organic deposits should be analyzed and complete testing should be performed to increase the productivity and ensure smooth operations.

This paper presents a comprehensive analysis procedure for heavy organic sample deposits collected from wells located in one of the oilfields in Saudi Arabia. The samples were collected from different sources such as production logging tools, pulling out a failed ESP, and lowering completion equipment. The hydrocarbon phase was removed by organic solvent and the precipitated solid materials were collected for a lab analysis and solubility test. An identification and evaluation of the organic deposit compositions were investigated using SARA analysis and coreflood techniques. Organic solvents are used to replace the aromatic ones in order to minimize the toxicity and health concerns.

Several testing techniques were used for better understanding of the collected samples including thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The TGA was used to determine the rate of thermal decomposition and measure and change in weight of the samples. Three temperatures were used, 180 °C, 550 °C, and 990 °C and the total weight loss values ranged from 19 to 66 wt% except for the oriental sample, which showed a 71%. The XRD was used to identify the complete structure of the samples and found that they are mainly carbonate of Calcite and Halite in which can be removed by acids like 15 wt% of HCI at reservoir conditions. A small fraction of dolomites, quartz, microcline, chlorite, and illite were identified as well. Static and dynamic solubility tests were performed with more solids observed in the static one. Two different soaking times: 3 and 24 h at both room temperature and 50 °C were implemented using 1:10 ratio of weight to solvent. The samples were found to be purely organic with between 20% and 60% asphaltene content. The performance of the solvents was negatively affected by the soaking time and better to be limited to 3–5 h.