Depletion of the reservoir leads to a decrease in production rate and continuously drops below its minimum critical velocity. At this point, the liquid which flows vertically upward with gas begins to fall back into the wellbore. Liquids accumulation in the tubing creates additional pressure drop and gives more flow restriction to surface. Smaller diameter tubing string (so-called, velocity string) installation is a simple yet successful methods applied in Semberah field to overcome liquid accumulation in wellbore of low production critical gas wells. This paper discussed case studies and screening improvement of velocity strings installation in the observed field. The project delivered an improvement of candidate screening and design to achieve the continuously flow after installation. Case studies were introduced in this paper as example of success and non-success application. Screening improvement was delivered based on post-mortem analysis. Selection candidate included identification of liquid loading symptom by well behavior, critical rate analysis on each wellbore section, and flow regime analysis. Pressure and temperature bottom-hole survey, either at static or flowing condition had to be provided and matched with velocity string model. Evaluation of new critical rate each wellbore section and new flow regime after installation must be calculated. This applied method was proven to extend production life and increase gas cumulative production in observed field. Better understanding of comprehensive well screening is an important factor to enhance success ratio of velocity string installation project. The improved screening based on field experiences can be used as a reference of velocity string selection candidate and design in other liquid loaded gas field. This paper also discussed further opportunities of un-success cases, which apply a tandem de-liquefaction technology: velocity string and wellhead compressor or gas lifted injection for gas well.

VICO Indonesia is an Oil and Gas company which has operated the Sanga-Sanga Production Sharing Contract (PSC) in East Kalimantan, Indonesia, since 1968. More than 750 development wells have been drilled to date in the harsh swampy environment of the Mahakam Delta in East Kalimantan. Today, the mature reservoirs are predominantly gas, extremely depleted, and have an average recovery factor of 70%.