ESTIMATION OF FORMATION AND CONDENSED WATER CHEMISTRY FROM WIRELINE FORMATION TESTER AND DST WATER SAMPLES: A CASE STUDY FROM ABADI GAS FIELD

摘要

For a gas field development, water chemistry is an important data for wireline logging data interpretation as well as facility designs, i.e. corrosion / scale / hydrate management, facility metallurgy, and sludge / waste water management. Especially for a remote and offshore gas field, it is critical because modifications of the existing facilities are very difficult and sometimes impossible. On the other hand, sampling and analysis of formation and condensed water chemistry is always embarrassed by contamination of drilling fluid filtrate, completion brine and, cement. There are many published studies and various commercialized sampling methods for iriinimizing the filtrate in the water sample. Specific sample preservation and measurement / analysis are also available for many important substances. In Abadi Gas Field, water samples were collected and analyzed in six exploration and appraisal wells by bottom hole sampling using wireline formation tester (WFT) as well as Drill Stem Test (DST) surface sampling. The samples taken by wireline formation tester were contaminated by potassium chloride (KCl) water base mud (WBM), and the samples taken by DSTs were supposed to be mixtures of formation water, condensed water, and KCl WBM. Sodium thiocyanate was used as a tracer in the drilling mud, however it didn't work perfectly as a reliable indicator because the concentrations were inconsistent among those measured at the rig site and those at the on-shore laboratory. This paper shows the original methods of estimating the formation water and condensed water chemistry which exploit the major ions' concentration as a package of contamination indicator as well as the tracer concentration. Lessons learned and future recommendation for water sampling and analysis are also introduced.