黔西比德-三塘向斜煤层气藏特征及甜点区段

Characteristics of coalbed methane accumulation in Bide-Santang syncline,western Guizhou and favorable sector

黔西比德-三塘向斜煤层气藏主要赋存于龙潭组Ⅰ、Ⅱ、Ⅲ3个煤组中,其中Ⅰ煤组6#和7#煤层、Ⅱ煤组16#和17#煤层、Ⅲ煤组20#、23#、27#、30#煤层分布稳定。煤层埋深受向斜构造控制明显,比德次向斜近轴部地区可达1500 m;煤岩以高变质的瘦煤、贫煤和无烟煤为主,最大镜质体反射率自西向东、由北到南逐渐增大;煤岩对甲烷吸附能力普遍较高(兰氏体积,18.32~39.32 m^(3)/t),区域上受煤变质程度影响显著;原位埋深条件下,煤岩渗透率较低,煤层含气量整体较高,平均10~15.78 m^(3)/t,含气饱和度普遍大于50%。结合该地区多层合采效果发现,比德次向斜埋深超过800 m的气井产气效果差,珠藏和三塘次向斜煤层气开发地质条件较好,其中珠藏向斜Ⅲ煤组4套主力煤层(煤层间距小于60 m)为潜在的高产优质储层。

The coalbed methane(CBM)resource in the Bide-Santang synclineis hosted in three coal groups of the Longtan Formation,of which the coal seam No.6 and 7 in groupⅠ,the coal seam No.16 and 17 in groupⅡ,and the coal seam No.20,23,27 and 30 in groupⅢare stably distributed.The seam depth is obviously controlled by syncline structure,reaching 1500m near the axis of Bide sub syncline.The coal seams are mainly high metamorphic lean coal,lean coal and anthracite,and the maximum vitrinite reflectance increases gradually from west to east and north to south.The methane adsorption capacity of coal is generally high(Langmuir volume,18.32~39.32 m^(3)/t),and is significantly affected by the coal metamorphism degree.Under the in-situ condition,the seams belong to typically low permeability reservoir,but with high gas content(average of 10~15.78 m^(3)/t)and high gas saturation(generally>50%).Combined with the effect of multi-layer co-production in this area,it is found that the gas production effect of the gas wells with the inclined depth of more than 800m in Bide is poor,and the geological conditions of coal gas development in Zhizang and Santangxi syncline are relatively good.Among them,four sets of main coal seams(seam spacing<60 m)ofⅢcoal group in Zhizang syncline are potential high-yield and high-quality reservoirs.