PVTX history of the North Sea's Judy oilfield

Volumetric liquid:vapour ratios generated using a Confocal Laser Scanning M icroscope are used along with PVT modelling software to estimate the compos ition, PT phase envelope and isochore of single petroleum inclusions in the North Sea's Judy field. The data are used to quantify pressure histories a nd to determine the compositional evolution of petroleum in the field. Impo rtant constraints are also placed on the permeability structure and history of the overlying chalk. Key conclusions are: (1) quartz cementation and th e emplacement of low Gas-Oil Ratio oil occurred 1-3 Ma ago in a significant ly overpressured regime; (2) the present gas condensate was formed by the i njection of gas-rich petroleum into a specific part of the field. Analysis of other North Sea fields suggests that many gas condensates form by the en gulfment of oils by later gas. (C) 2000 Elsevier Science B.V. All rights re served.