四川盆地中二叠统储层特征与勘探方向

Characteristics and exploration prospects of Middle Permian reservoirs in the Sichuan Basin

近年来,四川盆地中二叠统天然气勘探取得了可喜的进展,多口井在中二叠统茅口组、栖霞组白云岩孔隙型储层段钻获高产工业气流,中二叠统成为该盆地现阶段最现实的接替层系之一。为明确下一步的勘探方向,分析了四川盆地中二叠统的沉积背景和有利储层类型。结果表明:沉积环境主要为开阔台地浅水碳酸盐岩沉积环境;沉积时,古地貌西高东低,中西部生屑滩相储层较东部更为发育;地壳拉张使得中二叠统具备热水沉积、热液改造的良好条件;对勘探有利的3种储层类型为栖霞组滩相白云岩孔隙型储层、茅口组热水白云岩孔隙型储层和茅口组岩溶储层,其中白云岩孔隙型储层是中二叠统最有前景的勘探目标。结论认为:①川西北部—川中地区中二叠统灰质烃源岩生烃强度大,具有形成大中型气田的物质基础;②川西地区栖霞组白云岩储层较厚,是中二叠统天然气勘探的最有利地区;③上述3种储层类型均发育的地区主要分布在川中地区,其3套储层纵向上叠置,勘探潜力大;④剑阁—南充—丰都地区位于热次盆区带,其茅口组热水白云岩储层发育且叠加茅口组岩溶储层,天然气勘探前景好。

In recent years, encouraging progress has been made in Middle Permian natural gas exploration in the Sichuan Basin - nu- merous wells have obtained high-yield industrial gas flow in the dolomite porous reservoir sections in Middle Permian Maokou For- mation and Qixia Formation, making the Middle Permian one of the most realistic replacement strata at present. In order to clarify the further exploration prospect of the basin, the Middle Permian depositional settings and prospective reservoir types were analyzed. The results show that： （1） the depositional environment was predominantly open, shallow water; the palaeogeomorphology was high in the west and low in the east, with bioclast flat reservoirs more extensive in the middle-west part than the east part; crustal extension made Middle Permian deposits have good conditions for thermal water deposition and hydrothermal alteration; and （2） the prospect reservoirs for exploration were shoal facies dolomite porous reservoir of Qixia Formation, thermal water dolomite porous reservoir of Maokou Formation and karst reservoir of Maokou Formation, thus, dolomite porous reservoir was the most perspective target in Middle Permian. It is concluded that Middle Permian limestone source rocks have large hydrocarbon generation intensity in the northern part of Western Sichuan - Central Sichuan and have the material basis for the formation of large-medium gas fields; the thick dolomite reservoir of Qixia Formation ~,n tb, e Weste^cn S;,eb.uan Basin ;~s the most prospective reservoir in Middle Permian~ three types of reservoirs are distributed in the Central Sichuan, and they are superimposed vertically with large exploration potential; Jiange-Nanchong-Fengdu region is located in thermal sub-basin zone, where the thermal water dolomite reservoir of Maokou Forma- tion is pervasive and superimposed on the karst reservoir of Maokou Formation, showing good natural gas exploration prospects.