A Holistic Approach for Mitigating Scale Deposition in Highly Sour Gas Wells

Abstract

Formation of iron sulfide scale in the Khuff sour gas wells has been a persistent problem. Accumulation of scale deposits on downhole tubing and liner has resulted in significant operation problems, such as restricting wellbore surveillance, limiting downhole intervention, interfering with downhole logging, and damaging logging tools. Heavy scale deposition can also result in a significant reduction in well productivity when reaching perforated intervals. Extensive efforts have been devoted in recent years to solve this challenge, including scale composition determination, scaling mechanism investigation, evaluation and deployment of various descaling technologies, understanding formation damage mechanism and development of field trials of preventative methods. Removing such scales has been a challenging and complex process. Coiled tubing (CT) mechanical descaling was developed and deployed in the past, by taking advantage of state-of-the-art technologies such as high RPM milling, downhole sensors, foamed cleanup tools and sophisticated surface collecting/well testing equipment. However, CT descaling operations have become limited in recent years, due to reduced downhole pressures in some wells as field matures. This paper summarizes the holistic approach for mitigating scale deposition in highly sour gas wells, with emphasis on the results of field implementation of the newly patented scale dissolver (ISD) technology for dealing with the iron sulfide scales at high temperatures in the highly sour gas wells. Lab studies demonstrated that this chemical product have potentials to be use for both tubing/liner/completion and formation stimulation benefits as well. Field results showed significantly increased gas productivity in conjunction improved well operational factors, as well as retrieved well accessibility. A discussion on the different lab evaluation protocols is also presented and a final update on current scale clean-up strategies and future proposals are included. The results presented in this work represent the lately advancements on iron sulfide scale management. The new scale dissolver technology is under commercialization and can be applied in all various systems such as oil and gas producers, water injectors, and surface handling facilities.