川中磨溪地区龙王庙组沉积相与高频层序对储层的控制

CONTROL OF SEDIMENTARY FACIES AND HIGH-FREQUENCY SEQUENCES ON THE RESERVOIR OF LONGWANGMIAO FORMATION IN MOXI AREA,CENTRAL SICHUAN BASIN

利用磨溪地区龙王庙组钻井岩心、薄片和测井资料,开展了沉积相、高频层序和储层成因研究.识别出潟湖、滩间海、颗粒滩和云坪等4种亚相;将其划分为2个四级层序,各层序又包括3~5个五级层序,四级层序及体系域可良好对比.储层整体孔隙性较好,储集空间主要包括晶间(溶)孔、溶洞和裂缝,储集岩类主要为细晶云岩、粉晶云岩和颗粒云岩.沉积相和高频层序明显控制着有利储层的发育:颗粒滩和云坪是最有利的储集相,四级层序高位域的孔隙度明显优于海侵域,在四级和五级层序界面附近发育的早期岩溶对云坪和颗粒滩储层物性改善起到关键作用,也为埋藏岩溶和表生岩溶改造奠定基础.

Four sedimentary subfacies of lagoon,inter-shoal sea,grain shoal and dolomitic flat of the Longwangmiao Formation in Moxi area,Central Sichuan Basin are identified by study on the sedimentary facies,high-frequency sequences and reservoir genesis base on the drill cores,thin sections and logging data.The Formation can be divided into two fourth-order sequences while each includes three to five fifth-order sequences separately.The porosity of reservoirs is generally good with the main reservoir space as intercrystalline pores,solution caves and fissures,the main reservoir rocks being finely crystalline,silty and grained dolomites.The favorable reservoirs are obviously controlled by sedimentary facies and high-frequency sequences.Grain shoals and dolomitic flats are the most porous reservoir facies.The HST in the fourth-order sequences usually shows better reservoir quality than the TST.Early stage dissolution developed near the fourth and fifth order sequence boundary plays the key role on the porosity improvement of dolomitic flats and grain shoals and also provides basis for the later stage burial dissolution and telogenetic karstification.