Abstract
A subsurface uncertainties is a possible future event, which, if occurs, would affect project objectives either negatively or positively. For any given model or event, the uncertainty is the range of variation of the component parts and possible outcomes. It could be quantified approximately by either analytical model or in a more cumbersome one such as numerical approach. This paper summarizes thedetermination ofuncertainties by DST analysis in appraising and developing the ST-X gas condensate field, which is offshore Vietnam in Block 15-1O. Drill Stem Test (DST) results show that the S field has moderate to low permeability, multiple flow boundaries/barriers, and at least 2 PVT regions. To understand the impact of these and other important reservoir parameters on ultimate gas and condensate recovery and well count, the uncertainties has to be well evaluated and understood. The study demonstrates that there is a wide range of possible ultimate gas and condensate recoveries and well counts. The top causes for this wide range are permeability and flow boundaries/barriers. In addition to the subsurface risks, drilling cost of a ST-X well is very high. The high well cost in combination with the field being offshore, having low permeability and possibly numerous reservoir compartments dramatically increase the risk of a full field development.
Highlights
The ST-X field is in the Cuu Long basin with approximately 155 km east of Vung Tau, 62 km offshore Vietnam, in 66 meters of water (Figure 1)
Theresults of this work show that there remains significant reservoir uncertainties in the ST-X field and thesimulated recovery factor can vary greatly
Field, it was found that the drilling cost of a ST
Summary
The ST-X field is in the Cuu Long basin with approximately 155 km east of Vung Tau, 62 km offshore Vietnam, in 66 meters of water (Figure 1). Four wells have been drilled in the ST-X field to date (Figure 2). The first wildcat well,Well-Alies in the South East corner of Block 15-1O. Tests showed hydrocarbons flowing from three intervals in the Oligocene Clastics. SCIENCE & TECHNOLOGY DEVELOPMENT, Vol 19, No.K1- 2016 Well-Bwas drilled to evaluate the faulted and fractured basement reservoir, as well as, the Oligocene sandstones sequences. - Static Uncertainties mainly impacting STOIIP (from structural, depositional and fluid contact uncertainty). - Dynamic Uncertainties impacting long term reservoir sweep and productivity. These categories of uncertainties combined describe a range of ultimate recoveries and production forecasts
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