Abstract
This paper summarizes theuncertainties and challenges in appraising and developing the ST-X gas condensate field, which is offshore Vietnam in Block 15-1. Drill Stem Test (DST) results show that the ST-X 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, a reservoir simulation study was performed. 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 the heterogeneity in permeability distribution 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
The final build up pressure being lower than the initial pressure for all Drill Stem Test (DST)’s was interpreted as restricted flow barriers and/or significant reductions in permeability with increasing distance from the wells (condensate blockage was observed occurring on one DST as the bottom hole flowing pressure (Pwf) dropped below the dew point pressure (Pd))
Theresults of this work show that there remains significant reservoir uncertainties in the ST-X field and thesimulated recovery factor can vary greatly
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. Four wells have been drilled in the ST-X field to date (Figure 1). 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. The second well (or the first appraisal well) Well-Bwas drilled to evaluate the faulted and fractured basement reservoir, as well as, the Oligocene sandstones sequences. The second appraisal well,Well-Cwas drilled to evaluate the down flank extent of the sand sequences and an untested fault block. The Well-Dwell was drilled to test the Oligocene clastics on the northern flank of the ST-X structure
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