四川盆地石炭系黄龙组储层特征及主控因素分析

Reservoir characteristics and main control factors of the Carboniferous Huanglong Formation in Sichuan Basin

石炭系黄龙组为四川盆地天然气藏的主力产层,经过多年的勘探开发工作,目前已进入地层-岩性油气藏勘探阶段,因此加强对该区储层发育特征及分布预测研究显得尤为重要。文中以精细岩心观察和薄片鉴定为基础,结合扫描电镜、物性和孔隙结构等资料分析,对该区储层发育特征及主控因素进行分析,预测了该区有利储层分布区域。研究表明,四川盆地石炭系黄龙组主要发育局限台地潮上坪-潮间坪-潮下坪沉积,其中潮间-潮下坪中浅滩微相沉积发育;储层岩石类型主要为(残余)颗粒白云岩、粉-细晶白云岩和云质岩溶角砾岩,储集空间以晶间孔、晶间溶孔为主,粒间溶孔、粒内溶孔、铸模孔和裂缝次之;储层孔隙度分布范围为0.03%~30.67%,平均值为2.59%,渗透率分布范围为0.001~290mD,平均值1.56mD,为低孔特低渗裂缝-孔隙型储层,孔渗相关性较好,孔喉组合以小孔-中、细喉为主。该区储层发育主要受岩性、沉积相、成岩作用及后期暴露岩溶作用等因素控制,其中浅滩相颗粒云岩和潮坪相晶粒云岩原始储层物性较好,控制了储层分布的范围及规模;后期白云化作用是储层形成的基础,具多期次、多成因的特点,其中以准同生期和早成岩期白云石化作用对优质储层形成最为有利;古岩溶作用扩大储层范围,其分带性及不同溶蚀带的岩溶流体水动力条件、岩性特征及古地貌环境对岩溶储层空间展布规律和发育规模具直接控制作用,是提高储层质量的关键。根据该区白云岩厚度分布图、云质岩溶角砾岩厚度分布图和储层孔隙度分布图,选择孔隙度大于3%的等值线作为约束边界,预测出研究区有利储层分布区域,其中Ⅰ类储层7个、Ⅱ类储层5个,上述研究成果对该区储层预测及天然气勘探具有重要指导意义。

Carboniferous Huanglong Formation is the main producing formation of gas reservoir in the Sichuan Basin. Through years of exploration and development work, it has entered the stratigraphic^lithologic gas pool exploration stage Therefore, it is especially important to strengthen the research of the reservoir characteristics and distribution prediction in the study area. Based on abundant core observation and thin section analysis, combined with the SEM, reservoir physics and pore texture research, this paper analyzes the reservoir development characteristics and main control factors and predicts the potential reservoir distribution area. Studies show that Carboniferous Huanglong Formation in the Sichuan Basin developed restricted platform supratidal flat-intertidal flat-subtidal flat; among them, the intertidal flat-subtidal flat shallow shoal microfacies were developed; the dominant lithologic units are grain dolomite （or its remnant）, crystalline powder-cryptomere dolomite and dolomitic karst breccias; The noticeable reservoir spaces are intercrystalline pore and intercrystalline dissolved pore, while the secondary pore types are intergranular dissolved pores, intragranular dissolved pores, moldic pores and fractures; the porosity of Huanglong Formation ranges from 0. 030//00 to 30. 670//00, average 2.59 ~, while the permeability ranges from 0. 001 t,m2 to 290 X 10 a ~tm2 , average 1.56 X 10 3 ~m2. The reservoir of Huanglong Formation is characterized by low porosity and extremely low permeability, as well as a relative good correlation between porosity and permeability, belonging to crack-pore reservoir; the pore- throat assemblages are dominated by small pore and medium-fine throat. The potential reservoir is controlled by lithology, sedimentary facies and late stage diagenesis; the reservoir physics of grain dolomite in shallow shoal microfacies and of crystalline dolomite in tidal flat facies are better; sedimentary mierofacies controlled the distribution range and scale of reservoir; deuteric dolomitization is the foundation of reservoir formation, it is characterized by multi-stages and multi-causes; among all of and early diagenetic dolomitization are most beneficial to the the dolomitization stages, the penecontemporaneous formation of potential reservoir; paleokarst events could enlarge the reservoir scales, and its zonation, the fluid hydrodynamic condition and lithology in different dissolution, and microtopography are the direct control factors of karst reservoir spatial distribution patterns and development scales; paleokarst events are the key to improving the quality of reservoir. According to the dolomite thickness map, dolomitic karst breccias map and reservoir porosity map, we chose the contour lines that exceed 30//00 as a constraint boundary, predicted and among them, we have evaluated 7 reservoirs in the lebensraum of potential reservoir in the Sichuan Basin, rank I, and 5 in rank II. The results above-mentioned have important effects on the reservoir anticipation and gas prospecting in the Sichuan Basin.