从渤海湾盆地海陆对比看渤海海域天然气勘探前景

渤海湾盆地包括陆区和海域 (渤海海域 )两部分。油气勘探揭示 ,渤海湾盆地以产油为主 ,目前陆区所发现的气藏多为小型气藏 ,单个气藏的储量一般低于 5 0亿 m3,并以伴生气为主 ,4个储量较大的气田 (探明储量超过10 0亿 m3)主要为煤型气或高—过成熟气。渤海海域在油气勘探过程中也不断有气田发现 ,其中 JZ2 0 - 2气田已投入开发。与周缘陆区相比 ,海域天然气藏形成条件优越 ,其原因在于 :(1)自渐新世以来 ,整个渤海湾盆地的沉积中心逐渐向海域迁移 ,致使海域第三系沉积巨厚 (最大厚度超过万米 ) ;(2 )海域处于地幔隆起的核心地带 ,大地热流值较周缘陆区高 ;(3)海域比周缘陆区多一套东营组下段烃源岩 ,其生气能力较强 ;(4 )海域盖层条件比周缘陆区好 (海域第三系发育两套区域盖层 )。据近期资源评价结果 ,海域天然气资源量为 12 2 93亿 m3,但目前探明程度很低 ,随着勘探程度的不断提高 ,相信海域将会有更多、更大的气藏被发现

AN ANALYSIS OF OFFSHORE GAS EXPLORATION POTENTIAL IN TERMS OF COMPARISON BETWEEN OFFSHORE AND ONSHORE AREAS IN BOHAI BAY BASIN

Bohai Bay Basin is composed of onshore and offshore areas in geography.Oil and gas exploration results have revealed that it is mainly an oil production basin.For the onshore gas discoveries,most gas reservoirs are dominated by associated gas and less than 5 billion cubic meters in reserves,and other 4 bigger ones (over 10 billion cubic meters in proven reserves) are dominated by gas generated from coal material or gas in maturation to overmaturation.For the offshore area, gas fields have been finding continuously,in which JZ20 2 has been brought into development.Compared to the onshore area,there are much better conditions for gas accumulation in the offshore area:(1)The depocenter of the entire Bohai Bay Basin has gradually moved to the offshore area since Oligocene,resulting in much thicker Tertiary sedimentation, with the thickest section over 10,000 meters.(2)The offshore area may correspond a center of mantle bulge and is higher in geothermal flux than the onshore area.(3)In contrast to the onshore area, there is a Lower Dongying Formation source rock with higher gas generating ability in the offshore area.(4)There are two Tertiary regional seals offshore,forming a better sealing condition than the surrounding onshore area.The total offshore gas resources is estimated at 1229.3 billion cubic meters,according to a recent assessment,and it is believed that more and bigger gas fields will be discovered in the future,due to the present lower degree of exporation.