Transformation mechanism of muddy carbonate rock by the coupling of bioturbation and diagenesis:A case study of the Cretaceous of the Mesopotamia Basin in the Middle East

作     者：YE Yu LI Fengfeng SONG Xinmin GUO Rui YE Yu;LI Fengfeng;SONG Xinmin;GUO Rui

作者机构：Research Institute of Petroleum Exploration&DevelopmentPetroChinaBeijing 100083China CNPC Engineering Technology R&D Company LimitedBeijing 102206China 

出 版 物：《Petroleum Exploration and Development》 (石油勘探与开发（英文版）)

年 卷 期：2021年第48卷第6期

页      面：1367-1382页

核心收录：

学科分类：0820[工学-石油与天然气工程] 081803[工学-地质工程] 08[工学] 0818[工学-地质资源与地质工程] 0708[理学-地球物理学] 

基　　金：Supported by the China National Science and Technology Major Project(2017ZX05030-001)。 

主　　题：bioturbation muddy carbonate rocks Mesopotamia Basin Cretaceous diagenesis dissolution dolomitization 

摘      要：The transformation mechanism of muddy carbonate rock by the coupling of bioturbation and diagenesis was stud-ied based on core,cast thin section and physical property data of Cretaceous strata in the Mesopotamia Basin,the Middle East.There are 3 ways of biological transformation of rocks:(1)The living creatures transformed formations mechanically to make the rocks looser and intergranular pores increase.(2)After formation,burrows were backfilled with coarse-grained debris,and then unsaturated fluid infiltrated into the burrows during the penecontemporaneous period,resulting in dissolution.(3)Chemical alteration occurred in abandoned burrows and dolomitization produced a large number of intercrystalline pores.The·coupling of bioturbation and dissolution occurred mainly in the penecontemporaneous phase,and was controlled by rock type,sea level decline,burrow abundance,infillings,and water environment etc.As the burrows had better physical properties than the matrix,unsaturated fluid preferentially migrated along the burrows,leading to dissolution and expansion of the burrows first and then dissolution of the matrix.The coupling of bioturbation and dolomitization occurred mainly in the burial phase.The rich organic matter and reducing bacteria in the burrow provided material basis,reducing conditions and alkaline envi-ronment for dolomitization.The metasomatism in the penecontemporaneous period had little effect on the physical properties of the burrows.When the burrows were se parated from the deposition interface,equimolar metasomatism occurred in the burrows in a closed environment,forming euhedral fine-crystalline dolomite with intercrystalline pores.The transformation degree of bioturbation to muddy carbonate reservoir depends on rock type,density,connectivity,infillings and structure of the burrows.With the increase of the carbonate mud content,the im provement to rock physical properties by bioturbation be-comes more prominent.When the burrows are filled with coarse-grained debris or fine-crystalline dolomite,the greater the density,the higher the connectivity,and the lower the tortuosity of burrows,the better the physical properties of the muddy carbonate rocks are.