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The Tazhong reef-flat oil-gas field is the first large-scale Ordovician organic reef type oil-gas field found in China.Its organic reefs were developed in the early Late Ordovician Lianglitag Formation,and are the first large reefs of the coral-stromatoporoid hermatypic community found in China.The organic reefs and platform-margin grain banks constitute a reef-flat complex,mainly consisting of biolithites and grainstones.The biolithites can be classified into the framestone, bafflestone,bindstone etc.The main body of the complex lies around the wells from Tazhong-24 to Tazhong-82,trending northwest,with the thickness from 100 to 300 m,length about 220 km and width 5-10 km.It is a reef-flat lithologic hydrocarbon reservoir,with a very complex hydrocarbon distribution:being a gas condensate reservoir as a whole with local oil reservoirs.The hydrocarbon distribution is controlled by the reef complex,generally located in the upper 100-200 m part of the complex,and largely in a banded shape along the complex.On the profile,the reservoir shows a stratified feature,with an altitude difference of almost 2200 m from southeast to northwest.The petroleum accumulation is controlled by karst reservoir beds and the northeast strike-slip fault belt. The total geologic reserves had reached 297.667 Mt by 2007.
The Tazhong reef-flat oil-gas field is the first large-scale Ordovician organic reef type oil-gas field found in China. Its organic reefs were developed in the early Late Ordovician Lianglitag Formation, and are the first large reefs of the coral- stromatoporoid hermatypic community found in China.The organic reefs and platform-margin grain banks constitute a reef-flat complex, mainly consisting of biolithites and grainstones. The biolithites can be classified into the framestone, bafflestone, bindstone etc.The main body of the complex lies around the wells from Tazhong-24 to Tazhong-82, trending northwest, with the thickness from 100 to 300 m, length about 220 km and width 5-10 km. It is a reef-flat lithologic hydrocarbon reservoir, with a very complex hydrocarbon distribution: being a gas condensate reservoir as a whole with local oil reservoirs. hydrocarbon distribution is controlled by the reef complex, generally located in the upper 100-200 m part of the complex, and largely in a banded shap e along the complex. On the profile, the reservoir shows a stratified feature, with an altitude difference of almost 2200 m from southeast to northwest. Petroleum accumulation is controlled by karst reservoir beds and the northeast strike-slip fault belt. The total geologic had had reached 297.667 Mt by 2007.