断层对致密砂岩气藏甜点区的控制作用——以四川盆地中部蓬莱地区须二段气藏为例

Control action of faults on the sweet spots of tight sandstone gas reservoir: A case study of the second Member of Xujiahe gas reservoir in the Penglai area, Central Sichuan Basin

四川盆地中部上三叠统须家河组为大面积、低丰度致密砂岩气藏,天然气储量规模大、开采难度大、开发效益低,如何预测和精细刻画甜点区已成为提高气藏开发效益急需解决的技术难题。为此,以川中蓬莱地区须二段气藏为例,在总结储层特征和气井产能地质控制因素的基础上,明确了3种类型断层的地质特征和地震响应特征,研究了3种类型断层对储层甜点区的控制作用,并结合地震处理成果精细刻画了蓬莱地区须二段储层甜点区,同时分析了该成果的应用效果和前景。研究结果表明:①蓬莱地区须二段储层为低孔隙度、特低渗透率的致密砂岩储层,基质砂岩储渗品质差,断层伴生的裂缝是获得天然气高产的关键因素;②须家河组发育北西向逆断层,主要形成于燕山期,叠加定型于喜马拉雅期;③须二段断层向下均消失于雷口坡组,根据向上消失层位划分出3种类型,3类断层控藏效果差异显著;④Ⅰ类断层向上消失于主力产层段须二3亚段,对致密砂岩改造效果明显优于其他两类,伴生的裂缝发育异常带宽度介于几百米至几千米,其控制的须二3亚段成藏系统中源、储、盖等成藏要素搭配最佳,控制油气的富集高产;⑤断层控制裂缝发育带在常规地震剖面上呈现为大范围波形杂乱、错断等变异特征;⑥Ⅰ类断层控制储渗体甜点区17个,面积32.96 km^2,估算天然气地质储量为82.4×10^8 m^3。结论认为,该研究成果为蓬莱地区须二段气藏下一步的井位部署提供了支撑,具有较好的应用前景。

The Xujiahe Formation of Upper Triassic in the central Sichuan Basin is an extensive low-abundance tight sandstone gas reservoir with large-scale natural gas reserves,but its production difficulty is high and development benefit is low.In order to improve its development benefit,it is in urgent need to solve the technical difficulty of predicting and precisely characterizing sweet spots.In this paper,the gas reservoir of the second Member of Xujiahe Formation in the Penglai area of the Central Sichuan Basin was taken as an example.Firstly,the reservoir characteristics and the geological control factors of gas well productivity were summarized.Then,the geological characteristics and seismic response characteristics of three types of faults were defined,and their control action on sweet spots was investigated.Finally,combined with the seismic processing results,the sweet spots in the second Member of Xujiahe Formation in the Penglai area were characterized precisely.What's more,the application effect and prospect of this achievement were analyzed.And the following research results were obtained.First,the reservoir in the second Member of Xujiahe Formation in the Penglai area is a low-porosity and extra-low-permeability tight sandstone reservoir and its matrix sandstones are poor in preserving and permeating quality,so the fault-associated fracture is the key factor of high gas yield.Second,in the Xujiahe Formation are developed NW striking reverse faults,which are mainly formed in the Yanshan period and overlapped and finally shaped in the Himalayan period.Third,all faults disappear downward in the Leikoupo Formation.And based on the upward disappearance horizons,the faults are divided into three types.These three types of faults are obviously different in reservoir control effects.Fourth,typeⅠfault disappears upward in the principal producing pay,i.e.,the third Submember of second Member of Xujiahe Formation,and its reworking effect on tight sandstones is significantly superior to the other two types of faults.The abnormal development belt of its associated fracture ranges in width from several hundred to several thousand meters.Its controlled hydrocarbon accumulation system of the third Submember of second Member of Xujiahe Formation is optimally matched in the hydrocarbon accumulation elements of source rock,reservoir and cap rock.It controls hydrocarbon enrichment and high yield.Fifth,the fault-controlled fracture development belt presents abnormal characteristics in the conventional seismic section,e.g.bad break and chaotic waveform in the large area.Sixth,there are 17 sweet spots of reservoir body under the control of typeⅠfaults,which cover an area of 32.96 km^2 and have an estimated gas in place of 82.4×10^8 m^3.In conclusion,the research result provides support for the following well deployment in the gas reservoir of the second Member of Xujiahe Formation in the Penglai area,presenting a promising application prospect.