Thermodynamic Modeling Approach Assists Mitigation of Wax Deposition

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 211943, “Prediction and Prevention of Wax Deposition in MERO-006T: A Thermodynamic Modeling Approach,” by Obiora Nwosu, Olugbenga Daodu, SPE, and Basil Ogbunude, SPE, Shell, et al. The paper has not been peer reviewed. _ Well MERO-006T is an oil development well that came into production in March 1988 and has been plagued with incessant wax buildup. Research indicates that a wax-inhibition tool can be deployed in the well. The complete paper highlights the thermodynamic modeling approach adopted to determine the wax appearance temperature (WAT) in Well MERO-006T, the well-modeling approach to estimate the depth at which wax formation would occur, and the optimal depth for the wax-inhibition tool based on life-cycle-production expectations from the well. Introduction Problems associated with wax deposition can occur anywhere in the production system, from the reservoir to the terminal. Wax deposits result from the cooling effect of oil flowing from high-pressure reservoirs through the wellbore to the surface. Depressurization of the oil as it is produced leads to its expansion and temperature drop, which induces crystallization of wax. Considering the effects of wax deposition on producing wells and facilities, prevention of the phenomenon is preferable to correction. Challenges Well MERO-006T was drilled and completed as a single-string single in November 1981 on the Q2100X sand. The crude oil in the reservoir is waxy and has resulted in several wax-cutting jobs across the production life of the well. By February 1989, the production rate had declined to 198 BOPD on 28/64-in. bean. A dewaxing job was completed, and production rose steadily, peaking at 1012 BOPD at 195-psig tubinghead pressure and 0% basic sediment and water in May 1991, after which the well quit production because of wax by November of that year. Several unsuccessful attempts were made to produce the well until March 1994, when stimulation, wax cutting, and nitrogen-lifting intervention was performed. In April 1994, the interval produced dry at an average rate of 160 BOPD on 36/64-in. bean until January 1995, when it quit again. Wax cutting was performed in June 1997; the interval produced dry at an average rate of 300 BOPD on 36/64-in. bean. The well produced at approximately 300 BOPD until March 2003, when production rate dropped to 170 BOPD. Solvent soak and dewaxing was performed in Q4 2004, and the well was opened to flow; production fluctuated between 500 and 100 BOPD. The well was closed in for low productivity as the result of wax formation in October 2005. However, in 2017, the well’s B annulus pressure was found to be higher than maximum allowable annulus surface pressure at the wellhead. Post-risk assessment, the well was classified as high-risk. In 2018, a remediation using conformance control was performed, but this was unsuccessful. It was decided to carry out a workover to restore well integrity. The cumulative production from this interval has been recorded as 1.485 million STB.