Print this pageAbnormal High Temperature and Overpressure and Gas Exploration in Yinggehai Basin South China Sea
QI ZUOMING, WANG YAN
Yinggehai basin is one of the most prospective Tertiary basin characterized by high temperature and overpressure and abundant gas resources.
The geothermal gradient of the basin is 4.5-6.12 degrees C/100m, and 2.2 of pressure coefficient. By geological and seismic data, the geothermal source are mainly from heat flow of upper mantle, and as a result of diapirism and thermal effect of the high energy fluid, not only diapir anticlines were formed, but also pyrolysis hydrocarbon gas and CO[2] were produced.
Diapir structures are the weak spots where high energy fluid releases, and also the places for gas accumulation. The diapirs contain a high contents of CO[2] and certain quantities of gas. The high energy fluid squeezes out the original accumulated gas from the trap and occupy a part of the spaces resulted in forming a zone with high concentrations of CO[2]. Along the flanks of the diapirs, the original gas is not scattered and disappeared by the obstruction of high pressure and migrate to the low pressured synclines.
Up to date, giant gas pools have been discovered in upper Yinggehai formation. Recent further studies show that large anticlines related to diapir were well developed in deeper part of the basin, such as Huangliu formation dominated by low stand or delta fan system and turbidity sandstone; and Meishan formation which is identified as deep marine turbidite, particularly low pressured Huangliu formation is between the two high pressured layers which indicates that early world-class gas pools may be preserved.