Contribution of Sampling-While-Drilling Technology to Incremental Reserves, Adding Value to Field Knowledge, Avoiding Multiple Drill Stem Tests and Saving Rig Days - A Case Study From the TGT Field, Vietnam

Abstract

Sampling-while-drilling technology has quickly evolved into an established service and has been used in varied scenarios with object-oriented applications. This case study presents the application of fluid analysis and sampling while drilling a development well in the Te Giac Trang (TGT) field of Vietnam. The application of this technology contributed to accruing reserves, provided a deeper understanding of the production area, and avoided further drillstem testing, thereby saving numerous rig days. The principal challenge was to reduce the uncertainty in reservoir fluid type that remained after drillstem testing results from the exploration phase. The objectives included confirming the formation fluid type in two reservoir units, formation pressure regime and determining the pressure communication with the production area. The aim was also to avoid three more planned drillstem tests. Timing was critical, so two runs were planned strategically after the hole section was drilled. The first run performed was formation pressure testing with fluid identification and sampling from 11 prioritized depth stations. The mobility ranged between 29.3 and 128.1 mD/cP. The cleanup duration and volume ranged between 1 hour 14 minutes with 70.0 litres and 3 hours 7 minutes with 154.7 litres pumped respectively for the high- and low-mobility depth stations. A total of 1009.8 litres were pumped in 23.6 hours. The samples were sent immediately to the PVT laboratory for quick analysis. Despite the high levels of invasion expected during the cleanup and sampling operations, the contamination level was less than 10%; mostly between 4% and 8%; the lowest was 3%. Ten single-phase fluid samples were collected, out of which seven were oil and three were gas. As a result of the fast turnaround of the sampling results from the first run, the subsequent run performed was pressure testing only, with 61 depth stations. With a maximum overbalance of 1,381 psia (9,522 kPa) from both wiper trip runs, the sampling-while-drilling application provided excellent pressure repeatability with 100% sealing efficiency and representative formation pressure, mobility and fluid data. The planning of sequential runs with sampling to confirm fluid type followed by a run for additional pressure tests enabled the sampling-while-drilling technology to identify incremental reserves and avoid multiple drillstem tests, saving an estimated 35 rig days. The acquired pressure testing data added valuable information to the pressure communication dynamics between reservoir layers of the well and adjacent producing area of the field.