Abstract

The RFT tool (Schlumberger Trade Mark), is a well known and powerful tool for formation fluid sampling and formation pressure measurement. The objective of this paper is to stress some specific limitations of pressure measurements regarding height above free water level and fluid gradient calculation in multi-layered and multi fluid contact fields with non strictly hydrostatic behaviours. Actual field examples from the Mahakam Offshore PSC (Kutai basin, East Kalimantan, Indonesia) are presented. Regarding the calculation of distance to free water level, a brief review of the theory is given and the possible origins for inaccuracy in the final results are analysed. The particular case of the Tunu gas field is illustrated. The combined effects of poor petrophysical characteristics and varied hydrodynamic potential in relation to bad sand connection within a deltaic series are demonstrated. In the second part of the paper the emphasis is on the possibility of accurate determination of the nature of fluids in a depleted reservoir through a series of pressure measurements. Examples of confusing and sometimes misleading results obtained on the Handil oil field are illustrated. The possible sources of errors are also analysed, and practical rules are given on the minimum reservoir thickness necessary to get reliable fluid gradients.