Transition zone (TZ) refers to a certain height above the Free Water Level (FWL) where both hydrocarbon and water could potentially flow together. The two phases flow is not the definite situation based on the actual fields’ performance observation and it is an ongoing common misunderstanding with broad level of subjectivities for years. Lack of relevant experimental data and the insufficient physical understanding of the characteristics of the transition zone makes the modeling of both 3D static and dynamics to be challenging, subjective and finally uncertain when it comes to predictive capability.
The recent studies by the team and this paper aim to illustrate that in the transition zone due to the relatively lower capillary force, oil has usually occupied the bigger pores compared to the intervals above the transition zone and hence the oil is more prone to move. Also, under enough drawdown and differential pressure level where it could be sensed by aquifer, water could also be fed by aquifer through the established water film by capillary. However, the water saturation in the transition zone will not be reduced through production compared to the initial water saturation. Hence, the relative permeability curves should be cautiously developed to represent the flow condition in the transition zone.
Three oil rim developments in Malaysia with established transition zone and enough production & relevant surveillance history have been selected for this study. There is evidence from actual production data on dry oil recovery from transition zone between one to two years after those wells were put into production. Depending on the standoff of bottom perforated interval with oil water contact (OWC), water production onset may vary with time. Some of the fields have been placed with several horizontal wells in tapping the oil within transition zone to maximize recovery.
This paper will discuss an integrated multi-disciplinary views on understanding the flow characteristics and dry oil production from transition zone. Understanding the capillary pressure, depletion and drawdown strategy together with well completion design as well as location in respect with height above Free Water Level (FWL) is crucial in successful monetization of the transition zone.