川西坳陷二叠系礁滩相预测及油气远景评价

Prediction of reef-beach facies and evaluation of hydrocarbon resources on for Permian in Western Sichuan Depression

川西坳陷二叠系拥有巨大资源,具备发现大型气田的可能。为此,利用川西坳陷海相层序地层格架剖面,结合下古生界厚度图,对川西坳陷二叠系成藏条件进行了全面研究。首先分析了生烃中心的发育状况及运移通道;然后通过分析二叠系地震相异常,探索了长兴组、阳新统发育生物礁的可能,描述了阳新统溶蚀性储层发育的状况。研究结果表明:在震旦系-下古生界地层中,存在一个古坳拉槽——川西古坳拉槽,古坳拉槽边缘为大邑、龙泉山、老关庙3个大型古隆起,槽与隆起之间以基底断层过渡。古坳拉槽表现为复合三叉裂谷特征,盆地内的三联点大致在绵竹一带,二叠系绵竹-武胜台洼是古坳拉槽在峨眉地裂运动中的继承发展。在台洼两侧高部位,叠置沉积了阳新统-长兴组生物礁、滩。洛带-广汉长兴组具有典型的生物礁地震相,阳新统也可能发育生物礁。阳新统有较长时间的暴露,顶部发育大量缝洞、冲沟。因基底断层可构成热液运移通道,长兴组-阳新统生物礁、滩有可能发育孔隙性的白云岩储层。综合古坳拉槽巨厚生烃中心、阳新统-长兴组礁滩相发育,以及暴露溶蚀作用和潜在白云岩化储层等因素,预测川西坳陷二叠系阳新统-长兴组存在一个大型气田,两个层的圈闭资源量达15 207×108 m3,具有巨大的经济价值。

In the Western Sichuan Depression,Permian possesses huge resources and has the potential to discover large-scale gas reservoir.The carbonate reef-beach and the corrosive fracture-cave forms traps by themselves,so the research of reservoir is focused on Permian reservoir prediction.In order to study the accumulation conditions of hydrocarbon of Permian,the regional marine sequence stratigraphic framework profile,combined with the thickness map of Paleozoic,is utilized.The development and migration pathway of hydrocarbon genetic center are analyzed and then the abnormal of seismic facies are discussed to discover the possibility of developing reef-beach of Yangxin series and Changxing formation.Moreover,the characteristics of exposure surface of Yangxin series are depicted.The research results show that in the Sinian system-Lower Paleozoic strata,there is a Chuanxi palaeo-aulacogen,associated with three large-scale palaeo-uplifts,including Dayi palaeo-uplift,Longquan mountain palaeo-uplift and Laoguanmiao palaeo-uplift.The transition between the aulacogen and the uplift is the basement fault.The Chuanxi palaeo-aulacogen displays the characteristics of complex trigeminal rift,of which the basin triple point is roughly in the area of Mianzhu County.Meanwhile,the Chuanxi palaeo-aulacogen is characterized by inheritance,which gave rise to the Mianzhu-Wushengtai sag in Permian formation by the Emei taphrogenesis taphrogeny.At the high position of both sides of Mianzhu-Wushengtai sag,there are reefs and beaches of Yangxin series and Changxin formation,which are overlapped.Among them,the Luodai-Guanghan reef of Changxin formation has typical seismic facies of reef.There are also reefs in Yangxin series.Because of the long period of exposure in Yangxin series,amount of holes and gullies are developed at the top of it.Because basement faults can form hydrothermal migration channels,dolomitized porosity reservoir might develop in the reef-beaches of Yangxin series and Changxin formation.Considering of various favorable conditions,such as the giant hydrocarbon generation center in palaeo-aulacogen,the development of reef and beach facies,exposure and corrosion,as well as potential dolomitized reservoir,we predict that there is a large Permian gasfield in Western Sichuan Depression.The trap resources of the two formations are predicted to 15 207×108 m3,which is of great economic value.