Cracking Mature Subsurface Information in Complex Well Design

Abstract

After 29 years of production in the brown field T at Peninsular Malaysia, most of its main producing reservoirs are already depleted. Further data acquisition is crucial to resolve reservoir characterization issues, such as communication, depletion & compartmentalization. However, matured fields often have complex trajectories and depleted zones that succumb to losses during drilling. Hence, optimized data acquisition planning is required to combat both complex reservoir characterization and well operation risk. This paper will discuss the challenges from planning to execution of efficient data acquisition and trouble-free drilling in highly deviated well while having losses and without compromising acquired data quality. The main challenges identified are to log complex multi-stacked reservoirs in shoreface and mouth-bar environment, shifted fluid contact due to production, high inclination well trajectories, wellbore stability and logging in losses environment in depleted zones. Fluid mapping while drilling (FMWD) was brought in to assess the pressure and mobility profile of those depleted reservoirs. Additionally, fluid scanning stations were planned to confirm the fluid type and downhole reservoir sampling was planned in the virgin appraisal target. The result of data acquisition has been used for reservoir characterization in terms of pressure depletion, reservoir communication and compartmentalization. Despite the mud losses that occurred during drilling (5-50bbl/hr.), the logging operation was a success. The acquired data has led to a new understanding of the faulting area, sand continuity and reservoirs heterogeneity. The team managed to get sample of volatile oil which is 1m below the gas oil contact (GOC) and able to quantify CO2 concentration in gas & mixture phase (Oil +OBM filtrate). The result has also proved reservoirs compartmentalization that could not be seen and the log can be biased. This information is crucial in subsurface evaluation in developing matured fields. The decision to adopt the FMWD tool has helped logging operation to continue circulating with control flowrate, avoid well in static condition during long period (>45mins) of logging operation where it reduces the risk of stuck pipe. There was no operational issue of stuck pipe or differential sticking while logging in losses condition. Open hole data acquisition in mature field will always be relevant for reducing subsurface uncertainty. By deploying FMWD for real time data acquisition, the project team was able to save rig days by eliminating dedicated wireline trips and potential wiper trip post logging via conventional wireline. The value of the data acquired will also further reduce the project cost by optimizing the future well placement and well trajectory. The success achieved in this campaign can also be replicated into other brown field development that has the same challenges.