David Dyck, President and Chief Operating Officer of Ivanhoe Energy Inc. and Gerald Moench, President of Sunwing Energy Ltd., announced better-than-expected reservoir characteristics at Sunwing’s Zitong-1 gas well in Southwest China based on an analysis of logs from the Xu5 and Xu4 shallower target formations.
“The results of this evaluation significantly increase the upside natural gas potential in the 70-squarekilometre Guan structure to approximately 0.8 to 1.0 trillion cubic feet, double our previous view of 0.3 to 0.6 trillion cubic feet, Mr. Dyck said. “This is also very encouraging information relative to our view of the entire Zitong block where we see the potential for several trillion cubic feet or more of natural gas. As we proceed with drilling, logging and testing operations, we aim to demonstrate this upside potential.”
The Xu5 and Xu4 formations, originally considered as secondary targets to the deeper Xu2 formation, were encountered at depths between approximately 3,500 metres and 3,800 metres. The two formations were logged and casing has been successfully cemented in place. Drilling has resumed towards the deeper Xu2 formation at approximately 4,150 metres.
Guan is the largest known structure on Sunwing’s 2,669-square-kilometre block located in the heart of the prolific Sichuan gas basin.
Log data on Xu5 and Xu4 formations at Zitong-1
Data from the open-hole logs indicate the Xu5 and Xu4 formations most likely share the same pressure regime, with a total sand shale sequence of 357 metres, from 3,445 metres to 3,802 metres.
Within this sequence, up to 58 metres (190 feet) of primary sand package has been identified in four sand packages between 3,841 metres and 3,564 metres in the lower Xu5 formation with porosity ranging up to 13%, and an additional 22 metres (72 feet) of secondary reservoir sand in three sand packages between 3,592 metres and 3,801 metres in the Xu4 formation with porosity up to 8.5% (see accompanying schematic).
Log data indicate that gas shows were present throughout the Xu5 and Xu4 formations. Gas also was observed in the mud at surface while drilling through these formations. As indicated in the company’s October 5, 2010 news release, Sunwing encountered significant pressures while drilling through the Xu5 and Xu4 formations. High pressures potentially are a very positive characteristic of the reservoir, increasing flow rates and reserve quantities of any potential gas discovery.
Next steps at Zitong-1 well
Drilling at Zitong-1 will continue to a planned total depth of approximately 4,500 metres (14,764 feet). Horizontal drilling options will be determined after testing of the vertical wellbore is completed. Sunwing expects to reach total depth by the end of November.
Progress update on the Yixin-2 well
The Yixin-2 well is drilling ahead and has reached a depth of 3,700 metres (11,781 feet). Increased gas readings have been recorded in the drilling mud as drilling as progressed into and through the top of the Xu4 formation. The well is expected to reach total depth of 3,950 metres within the next week, when open hole logs will be run.
The Yixin-2 well is being drilled as a twin of Yixin-1, which was drilled by Sunwing in 2007, and generated significant, but unverified, gas flow rates, before being shut-in due to surface equipment complications.
Applying leading-edge technologies in Zitong
Sunwing’s development program in the Zitong gas block represents the application of leading-edge technologies that have been dramatically successful in similar fractures reservoirs in tight gas projects in North America. These include horizontal drilling to improve the chances of intersecting the natural vertical fractures, as well as multi-stage fraccing.
Sichuan is the oldest and one of the most productive gas producing regions of China. Sinopec and PetroChina have made significant gas discoveries from the Xu2, Xu4 and Permian formations in blocks adjacent to Sunwing's Zitong Block. Any gas produced in Zitong would be tied into an established local and regional gathering and sales distribution system.
Sunwing is the operator of the 659,840-acre (1,031 square miles) gas exploration block in Sichuan, and it holds a 90% Contractor Interest in a Petroleum Contract with PetroChina Company Limited. Mitsubishi Gas Chemical Company of Japan holds the remaining 10% Contractor Interest.