四川盆地北部上震旦统灯影组四段储层特征及其控制因素

对于四川盆地北部(以下简称川北地区)上震旦统灯影组四段储层特征和发育规律的研究大多数都基于全盆地灯影组沉积模式再结合区域地质背景加以推测,且在储层发育规律及控制因素方面尚未达成共识。为了给川北地区的油气勘探提供支持,利用岩心、常规及铸体薄片、物性、压汞等资料,研究了该区灯四段储层的特征及分布规律,分析了灯四段储层发育的主控因素及模式,并与川中地区进行了对比。研究结果表明:(1)川北地区灯四段储层岩石类型主要为藻凝块云岩、藻叠层云岩、藻屑云岩与砂屑云岩,储集空间主要为藻格架孔和粒内溶孔,储层类型包括丘核相孔洞型储层、丘坪相裂缝—孔隙型储层和浅滩相孔隙型储层;(2)储层主要发育在灯四段各亚段的中上部,一亚段以浅滩相孔隙型储层为主,二亚段以丘核相孔洞型储层和丘坪相裂缝—孔隙型储层为主;(3)灯四段储层主要受控于沉积相和成岩作用,丘核、颗粒滩和丘坪微相有利于储层的发育,岩溶作用和重结晶作用有利于孔隙的形成,早成岩期岩溶作用是丘滩相储层孔隙大规模增加的关键因素;(4)灯四段储层的形成与演化可划分为沉积—同生—准同生期原生孔隙形成、浅埋藏期原始孔隙减少、早成岩期次生孔隙大规模形成、中—深埋藏期次生孔隙调整等4个阶段;(5)对比川北地区与川中地区的灯四段储层,二者具有相似性但控制因素不同,前者为相控储层,而后者则受控于沉积相与岩溶作用。结论认为,阆中—元坝—广元—胡家坝一带为川北地区灯四段储层发育最有利区,南江—巴中一带为较有利区。

Reservoir characteristics and their controlling factors of the fourth Member of Upper Sinian Dengying Fm in the northern Sichuan Basin

The researches on the reservoir characteristics and development laws of the fourth Member of Dengying Fm, Upper Sinian in the northern Sichuan Basin, are mostly speculations based on the sedimentary models of the Dengying Fm in the whole basin, combined with regional geological setting, and no agreement has been reached in terms of reservoir development laws and their controlling factors. In order to provide the support for the oil and gas exploration in the northern Sichuan Basin, we studied the reservoir characteristics and distribution laws of the fourth Member of Dengying Fm using cores, conventional and casting thin sections, physical property and mercury intrusion data, and then we analyzed the reservoir development models of the fourth Member of Dengying Fm and their controlling factors and compared those in the central Sichuan Basin. And the following research results were obtained. First, in the northern Sichuan Basin, the types of reservoir rocks in the fourth Member of Dengying Fm are mainly algae clotted dolomite, algae stromatolitic dolomite, algae clastic dolomite and doloarenite, the reservoir space is mainly acted by algae framework pores and intragranular dissolution pores, and reservoir types include vuggy reservoir of bioherm core facies, fractured-porous reservoir of bioherm flat facies and porous reservoir of shallow facies. Second, reservoirs are mainly developed in the middle and upper parts of each submember of the fourth Member of Dengying Fm. There is dominantly the porous reservoir of shallow facies in the first submember, and the vuggy reservoir of bioherm core facies and the fractured-porous reservoir of bioherm flat facies in the second submember. Third, the reservoirs in the fourth Member of Dengying Fm are mainly under the control of sedimentary facies and diagenesis. The microfacies of bioherm core, grain beach and bioherm flat are favorable for the development of reservoirs, karstification and recrystallization are favorable for the formation of pores, and the karstification in the early diagenesis period is the key factor for the large-scale increase of pores in the reservoirs of bioherm beach facies. Fourth, the formation and evolution of the reservoirs in the fourth Member of Dengying Fm can be divided into 4 stages, i.e., the formation of primary pores in the sedimentation-syngenesis-penecontemporaneous period, the reduction of primary pores in the shallow burial period, the large-scale formation of secondary pores in the early diagenesis period, and the modification of secondary pores in middle-deep burial period. Fifth, the comparison between the reservoir of the fourth Member of Dengying Fm in the northern Sichuan Basin and that in the central Sichuan Basin shows that they are similar but their controlling factors are different. The former is a facies-controlled reservoir and the latter is controlled by sedimentary facies and karstification. In conclusion, the Langzhong–Yuanba–Guangyuan–Hujiaba area is the most favorable area for the reservoir development of the fourth Member of Dengying Fm in the northern Sichuan Basin, and the Nanjiang–Bazhong area is a relatively favorable area.