The Accurate Evaluation of 3-Phase Fluid Saturations in Cased Wellbores: A New Methodology Applied To the Algyo Field, Hungary

by Saloua Tiar (Baker Atlas) – (presenter), Veronica Pipics, Ilona Vegane (MOL), Roberto Nardiello, Fabio Brambilla

Abstract

This case history presents a new methodology for the determination of accurate three phase fluid saturations behind casing. The study refers to the Algyo Field, Hungary, which has the largest hydrocarbon accumulations in the Pannonian basin and is characterized by more than 70 oil and gas reservoirs in a mature state of exploitation. The production comes mainly from more than 2000 historical vertical wells, however recently several horizontal wells have been drilled to increase existing production levels, to target new hydrocarbon zones and to convert some good porous reservoir units to gas storage.

The monitoring of the changing fluid contacts in the multi-level sandstone reservoirs of this basin is a key component in the evaluation of the field production status. However since the formation water in this field has very low and variable salinity, and some areas have been subjected to water injection, the standard Pulsed Neutron Capture (PNC) sigma measurement method cannot differentiate oil from water in this environment. An alternative methodology was therefore required.

A new methodology was employed based on the confluence of three new-technologies: New instrument design, new model response characterization, and a newly developed gas saturation analysis algorithm. The integration of this and traditional analyses then provided a true three phase saturation analysis of the reservoir intervals, allowing appropriate reservoir management decisions to be taken.