Down hole gauges installed in Block 16/21 satellite wells have given invaluable real time data during extended well testing (Sterling and Blair) and have been extremely useful in gaining an understanding of Balmoral and Glamis well and reservoir behavior in the early stages of production.
The long term reliability of these systems has proved disappointing, highlighting the need for further engineering research and development in this area, particularly in sub-sea electrical connectors. It is hoped that experience gained with the reported systems will help others considering their use or those looking at further developments of down hole pressure systems.
The Balmoral Field, located in Block 16/21 and discovered in 1975, received Government development approval in 1984 after extensive appraisal drilling. The field has been developed with 19 sub sea wells, 13 producers and 6 injectors (Figure 1). Ten of the production well s were drilled through a template and the remaining three are tied back to the template via subsea flow lines. All of the six injectors were completed sub sea and tied back to the template by flow lines.
Beneath the Balmoral Field, in fractured Devonian sandstone, lies the Sterling Field. Oil in Devonian sands was observed in a number of appraisal wells in the area and in 1986, well 16/21a-2 was completed and tied back to the Balmoral FPV for an extended well test. At the satisfactory conclusion of the test the well was recompleted as a Balmoral Paleocene producer.
In 1989 two separate satellite fields, Glamis and Blair, were tied back to the Balmoral template. The Glamis Field is in the Jurassic sands to the south west of the Balmoral Field and has been developed with two producers and one injector. The Blair Field is in Paleocene sands partially overlying Glamis and has been appraised from a single production well on extended well test.
The subsea nature of the development in andaround Balmoral and the extensive use of satellite wells makes frequent re-entries for reservoir monitoring purposes both difficult and expensive. The decision was therefore taken at an early stage to install permanent down hole pressure gauges on all satellite wells tied back to the Balmoral template.
This paper covers the details of two different gauge systems which have been installed in the area. The reliability of the systems and how the data obtained from these gauges has been used is addressed. In the light of the operational experience gained, areas for further development in pressure monitoring systems are also discussed.
