Analysis of asphaltene deposition in Marrat oil well string: a new approach

Journal of Petroleum Exploration and Production Technology December 2016, Volume 6, Issue 4, pp 845–856 | Cite as Analysis of asphaltene deposition in Marrat oil well string: a new approach AuthorsAuthors and affiliations Mohammad Ali KargarpourAbhijit Dandekar Open Access Review Paper - Production Engineering First Online: 10 December 2015 1.6k Downloads 1 Citations Abstract The amount of asphaltene is usually the minimum portion of crude constituents; however, due to its negative impact on the well performance and the overall efficiency of oil reservoir management, a large number of mostly academic studies are directed toward understanding the asphaltene behavior and mitigation of its deposition in flow processes from reservoir to process facilities. Typically, a small number of these are actual case studies. Among them is the asphaltene deposition in Marrat oil well string. In this particular case, significant amount of valuable field data were gathered for a long period of time under controlled conditions. By carefully reviewing the presented data in the original paper, we concluded that re-analysis of the field observation results, for improved understanding of the asphaltene deposition process, is necessary. By recalling the concept of liquid loading in the gas wells, the reduction of flowing well head pressure is interpreted due to the left asphaltene solid micelles in the well string. Also, we judge that the process of asphaltene deposition in the production tubing is a ‘seating and carving’ dynamic process, and at a critical thickness, the amount of asphaltene ‘cutting’ increases which is responsible for further pressure drop in the well tubing. By performing fundamentally simple calculations, the amount of asphaltene ‘left’ in tubing and the amount of asphaltene ‘cutting’ are computed. Also the minimum oil flow rate to handle and remove the asphaltene micelles is estimated in the Marrat case. Finally, we propose certain recommendations for future data gathering and optimum handling operation of asphaltene precipitation and deposition in well string. KeywordsAsphaltene Deposition Tubing Terminal velocity Flocculation Marrat  Introduction Asphaltene deposition in the pores of reservoir, in the flow string of wells, in the flow-line, and in the surface processing facilities is a recognized problem that affects the management of oil reservoirs. A broad range of efforts are made to resolve the issue; however, because of the varying nature of asphaltene, it becomes difficult to quantitatively characterize its structure and behavior, thus precluding a globally accepted solution. In each case (reservoir), to circumvent the problem, a unique method is presented. Even this unique method needs some form of adjustment or modification before applying it to a specific case. A large number of researchers have worked on the issue. Their works can be categorized in two groups: those who investigate a theoretical model to justify the complicated behavior of asphaltene, and those who plan, set up, and perform a series of lab tests to formulate the asphaltene deposition. Of course, among them, there are researchers who attempt to utilize both approaches to demonstrate the robustness of their models. Unfortunately, few field data are available which are gathered under controlled conditions. In the mid 1960’s, Haskett and Tartera (1965) presented these types of data for Hassi Messaoud field in Algeria. In 2005, Alkafeef et al. (2005), in conjunction to propose a simplified method of predicting asphaltene deposition in tubing, published a set of gathered field data relevant to Marrat field of Kuwait. There are other case studies for investigation of asphaltene problem in oil production from different reservoirs. Kharrat et al. (2012) worked on one of the Iranian light oil reservoirs. The reservoir and bubble point pressure were reported as 9200 and 4500 psi, respectively. After modeling the reservoir, they investigated the asphaltene behavior during production and suggested by controlling the well production rate at the optimum situation mitigate the asphaltene flocculation and deposition. Galoppini and Tambini (1994) studied the ultra-deep Villafortuna-Trecate (VF-TR) field. The density of oil was 40°API, and the GOR and bubble point pressure were reported as 618 scf/STB and 2578 psi, respectively. By measuring surface variables (pressure and rate), they calculated the equivalent productivity index (PI eq). It was suggested that plotting the PI eq versus cumulative oil volume has a linear trend. Thus, the change in the slope of this line would be an indication of asphaltene deposition in the vicinity of well bore. So, from history of wells, one can find the critical PI eq at which the well should be stimulated for asphaltene removal. Sanada and Miyagawa (2006) reported the chemical treatment in one of Japanese oil reservoirs. They addressed the asphaltene deposition in the productio (...truncated)