Enhancing Unloading Operations on Intermittent Wells in an Offshore Carbonate Field in Abu Dhabi

Abstract

Abstract The objective of this paper is to demonstrate the results of a study conducted on the nature of intermittent wells and the methodology to enhance unloading and reactivation operations. Intermittent wells are defined as wells demonstrating a production time period followed by a significant shut-in period. The study was conducted in an offshore carbonate field located in north-west Abu Dhabi, consisting of three major non-communicating sub-reservoirs separated by alternating dense layers. The study encompassed wells located in a low-pressure area of the reservoir. The first aspect of this study encompasses an in-depth look at the different types of completion design utilized throughout the history of the field, specifically, the advantages and disadvantages of each type of completion. The remaining aspect of this study is divided into two major categories, the enhancement of the inflow performance relationship (IPR) and the improvement of the vertical lift performance (VLP). The improvements of IPR are divided into the improvement of reservoir pressure, improvement of bottom hole flowing pressure, and improvement in wellbore damage. These improvements of IPR are briefly analyzed due to the minimal short term benefits. The main focus of this study is the enhancement of VLP for individual intermittent wells due to the instantaneous and rapid production gains and benefits. Additionally, the relationship between IPR and VLP is demonstrated through the use of prosper analysis. During the current time period and condition of the field, the IPR of intermittent wells can be improved either by secondary recovery or by minimizing near wellbore damage. A case study of a vertical intermittent well is analyzed using pressure transient analysis to present the shift from a positive skin value to a negative skin value. The main focus of this study is the enhancement of VLP for intermittent wells. This is due to the advantageous nature and rapid noticeability of benefits from improvements in VLP. The different challenges that inhibit VLP of intermittent wells are discussed, as well as, the major methods utilized to counter these challenges. This paper will present possible solutions and improvements to prolong the production time, and thus, minimizing the downtime of these intermittent wells. Global solutions have been studied including decreasing the separator pressure from the main production complex in order to reduce the consequential backpressure, which in turn will reduce the flow-line pressure, and thus allow the intermittent wells to flow. Operational improvements have been analyzed such as utilizing equipment including larger diameter chokes in place of smaller chokes in order to decrease pressure losses. In addition, scaling and precipitates in relation to chokes are investigated. The majority of the intermittent wells with a low success rate of unloading operations to reactivate wells are equipped with A3 velocity valves. These valves are problematic in an offshore environment due to the dependency on the flowline pressure and the production rate. When a well’s flow rate is decreased below the lower limit of the A3 valve, for any reason, the well will seize to flow, and thus categorized as intermittent, if this occurrence is common throughout the wells life. The majority of the intermittent wells have seized flow due to low well head flowing pressures in comparison to the flow line pressure. Two major solutions have been determined. First, to reduce the main separator pressure by allowing slightly more gas into the liquid system and thus reducing the back-pressure created on the flow line. Second, an increase in the reservoir pressure has been achieved by closing in off-set wells during the production time of the intermittent wells. An alternating production and shut-in schedule has been developed to enhance productivity. This study is concluded by discussing the different types of equipment used to counter intermittency include surface ejectors and jet pump technology. This paper will provide information and ideas to enhance the productivity, maximize the recovery, and prolong the production life of intermittent wells suffering from low well head pressure and malfunctioning equipment. This study is specifically relevant to reservoir production under low pressure mechanisms.