鄂尔多斯盆地神府地区致密气成藏条件及成藏规律

Accumulation conditions and accumulation laws of tight gas in Shenfu area,northeast of Ordos Basin

鄂尔多斯盆地东北缘神府地区处于晋西挠褶带北段,西侧已发现神木气田,南侧已发现临兴气田,神府地区由于煤系烃源岩热演化程度低(Ro<1.0%),生烃能力有限,勘探鲜有突破。通过分析神府地区致密气成藏条件,揭示了其南北部成藏差异性及天然气富集规律。研究结果表明:(1)研究区煤系烃源岩生烃能力有限,自西南部向东北部生烃强度变弱,强度介于(2~14)×10^(8)m^(3)/km^(2),天然气近距离运移,仅在本溪组、太原组和山西组发育气层,自下而上的气砂比降低、含气饱和度降低,水砂比升高;(2)三角洲分流河道、三角洲前缘水下分流河道和障壁砂坝是甜点型储层,物性好,容易富气形成高产致密气藏;(3)在北部层间断层输导下,天然气可运移至盒八段局部成藏,但充注能力不足,表现为差气层、气水层和水层的互层;(4)东部断裂带发育大型断层,断距大,天然气逸散,无法形成致密气藏,仅发育气水层、水层。在以上认识指导下,指出神府区块西南部、中西部是成藏富集区。2021年,在区块西南部探明天然气储量超过20010^(8)m^(3)/km^(2),有力地支撑了该区致密气的勘探突破。

The Shenfu area in the northeast margin of Ordos Basin is located in the northern section of the Jinxi flexural fold belt,and the Shenmu gas field has been found on the western side,and the Linxing gas field has been found on the southern side.Due to the low thermal maturity(Ro<1.0%)of coal-measures source rock in Shenfu area,and the hydrocarbon generation ability is limited,there is little breakthrough in exploration.Through analyzing the tight gas accumulation conditions in Shenfu area,the accumulation differences between the north and south parts,and the enrichment laws of gas are revealed.The results show that:(1)The hydrocarbon generation capacity of coal-measures source rocks in research area is limited,and the hydrocarbon generation intensity reduces from southwest to northeast,ranging from 210^(8)m^(3)/km^(2) to 1410^(8)m^(3)/km^(2),and natural gas migrates a short distance,only developed gas layers in the Benxi,Taiyuan and Shanxi formations,with lowered gas-sand ratio,gas saturation and raised water-sand ratio from bottom to top;(2)Delta plain distributary channel,delta front underwater distributary channel and barrier sand dam are“sweet spot”reservoirs with good physical properties,which are easily enriched to form high-yield tight gas reservoirs;(3)Under the influence of interlayer faults in the north,natural gas can migrate to the reservoir formation of He 8 member.However,the filling capacity is insufficient,manifested by poor gas,gas-water and water layers;(4)Large faults are developed in the eastern fracture zone with large fault distance,causing gas escaping and aborted tight gas reservoirs,only gas-water and water layers are developed.Guided by the above understanding,it is pointed out the southwest and midwest of this block are accumulation areas,the proven gas in the southwest of the study area are more than 200×10~8m~3 in 2021,which strongly supports the breakthrough of tight gas exploration in this area.