Optimization and Rejuvenation of Mature Assets: Challenges and Solutions for Water Control in Gas Wells
Authors: Wahid Fazrie , Mukerji Parijat , Zaouali Zouhir 
Published: May 2016

This reference is for an abstract only. A full paper was not submitted for this conference.

As more fields advance towards the later stages of their life, there is a compelling drive to optimize production. It is necessary to understand the changing reservoir performance over time and therefore proactive surveillance plays a key role in achieving production optimization.

We present field examples that show the value of fit for purpose logging and diagnostic techniques leading to an enhanced understanding of well & reservoir performance. We are able to demonstrate the added value of these logs in terms of access to reserves, potential water shut-off opportunities and a better understanding of communication between different reservoir layers.

In addition, we show that in some cases, simply addressing the issue of water encroachment in the near wellbore area may only provide a short term solution to the overall water management scenario. The reason for this is mainly due to the speed of water crossflow in the formation, rendering water shut off solutions, at best, short lived. This includes the many methods of water shut off examined that are available across the industry. Over the longer term, more complex solutions are required such as managing the encroaching water front by creating an impediment to the flood front, and producing the encroaching water from selected sites in the field, hence reducing the overall water volumes in current producing wells. Hence, a combination of these three base solutions; addressing the near wellbore issue, create an impediment to the encroaching water front and producing the reservoir water from selective sites was shown to extend the life of the field and reduce the overall water production in producing wells.

This paper then describes the complex analyses required to design such novel solutions and looks at five specific cases of gas wells with water production issues. The objective of this work was to extend the life of these producing wells. To accomplish this objective and to increase production over the potential life of the field, a further 7 wells were included in the study. Some of these were considered either as water producers equipped with artificial lift pumps to manage encroached aquifer water, or to be revived and used as a means to release trapped gas by way of localized depressurization using ESP. Additionally, a well located close to where the aquifer water breached was identified for chemical injection to create an impediment to the encroaching aquifer water. Results indicate that using this complex solution, the field's lifetime can be extended to over 7 years compared to several months should only water shut off be applied to the producer wells.

To conduct the analyses, a novel workflow was introduced whereby a combined simulation work, field analysis and well intervention feasibility review were implemented concurrently. Compositional modeling, NODAL analyses and water diagnostic plots were simultaneously utilized. The reservoir engineering and modeling aspects are discussed, paying attention to the potential gas reserves, type of water encroachment evident and optimization forecast. The well architecture and PLT results were reviewed to identify potential well solution methods on a well by well basis. Problems on well lifting capacity were addressed and believed to be impacted by a combination of factors such as the rate and trend of water encroachment, potential gas rates and liquid loading issues, and equipment availability. Additionally, saturation of trapped gas across the reservoir was identified by utilizing historical production and logging data and an updated history matched reservoir model.