南海西北部莺歌海盆地WHJM36-9气田的储集性和流体特征

WHJM36-9构造位于莺歌海盆地中央泥底辟构造带的东南端,该构造是在红河断裂右旋走滑运动所派生的东西拉张应力下形成的近南北向泥底辟伴生构造,WHJM36-9气田即位于该构造上,属于一个由背斜和断层控制为主的构造型浅层气藏。气田各层构造高点基本重合,但深部构造幅度明显大于浅层;气田储层主要为第四系乐东组(QpL)和新近系上新统莺歌海组一段(N2Y1),其岩性主要为中细砂岩—泥质粉砂岩。通过对气田岩心物性分析及地质综合评价,第四系乐东组一段储层属高孔高渗—中低渗类型,乐东组二、三段及上新统莺歌海组一段属高孔中渗的储层类型,该区的低阻气层则主要属高孔中低渗储层类型;气田天然气中烃类以CH4为主,C2以上组分含量较少(0.49%~2.71%),属高熟干气藏;乐东组和莺一段地层水分别为CaCl2和NaHCO3水型;气田各气组具有不同的压力和气水系统,为正常压力系统。

RESERVOIR PROPERTIES AND FLUID CHARACTERISTICS OF WHJM36-9 GAS FIELD IN YINGGEHAI BASIN,NORTHWESTERN SOUTH CHINA SEA

The WHJM36-9 structure, a mud diapir associated structure extending in south-north direction, is located in southeast of the mud diapir tectonic zone of the Yinggehai Basin, which was formed under the east-west tensile stress derived from the dextral strike-slip movement of the Honghe Fault. The WHJM36-9 Gas Field, that is located in the mud diapir associated structural traps, belongs to a tectonic type of shallow gas reservoir controlled by anticlines and faults. The structural highs of each gas reservoir in this gas field are basically of coincidence, but the deeper structural amplitude is much greater than the shallow ones. The main reservoirs of the gas field are the Quaternary Ledong Formation (QpL) and the first member of the Pliocene Yinggehai Formation (N2Y1), and dominated by medium-fine sandstone and argillaceous siltstone. Based on the results of core physical property analysis and comprehensive geological evaluation, we found that the first member of QpL is the type of reservoir with high porosity and high to mid-low permeability. The second and third members of QpL and the first member of N2Y1 are the types with high porosity and medium permeability. The low-resistivity gas reservoir of this region is mainly the type of reservoir with high porosity and mid-low permeability. The WHJM36-9 Gas Field is a highly matured dry gas field, of which the main hydrocarbon is CH4 with low C2+ (0.49%~2.71%). The formation water is CaCl2 type for QpL and NaHCO3 type for N2Y1. Each gas reservoir has its own formation pressure and gas-water system, and the formation pressure system is normal.