A Study On The Characterization Of The Pore Throat Structure Of The Cretaceous Mishrif Formation In The H Oil Field In Iraq

The bio-clastic limestone reservoirs of the Cretaceous Mishrif Formation in the H oilfield,Iraq,are affected by both sedimentation and diagenesis.For the Mishrif Formation reservoirs,the pore types are diverse,the pore-throat structures are complicated,the correlation between porosity and permeability is not obvious,kinds of reservoirs and the interlayers are spatially overlapping,and their heterogeneity is common.Along with the acceleration of oilfield production,there are practical problems such as uneven utilization of reservoirs,large pressure deficits and uneven distribution to occur,which were caused by the backward research on the reservoir heterogeneity with respect to the oil and gas exploitation.The study on the characterization of the pore-throat structure is the most imporant by now.According to the drilling core observation and description,microslide identification,micrograph and experimental data analysis,this study analyses quantitatively the characterization of pore-throat structure and discusses the rock type,diagenesis and faciessequence structure,which play an important role on the development of the porethroat structure.Finally,the author proposes a new developent model for the pore-throat structure,which can provide the guidance for identifying the interlayers and the theory for the water injection and efficient deployment.Three aspects of achievements in this thesis were obtained as followed below:(1)Based on the analysis of the case slice and high-pressure mercury injection experiment,it is recognized that the primary pores in the Cretaceous Mishrif Formation reservoirs are composed of the body cavity pore,the biological lattice pole,the intergrandular pore,and the micropore and the secondary pores contain the dissolved pores between the granules,the dissolution holes,the intrapartered dissolved holes,the mold holes,and the intergranular pores.The pore-throat combination can be divided into five types,such as intergranular pore-dissolution hole,intergranular pore,isolated-connected pore,isolated pore,microporous-isolated pore,and microporous pore.(2)This study quantitativly analyzed the influence of pore structure of carbonate reservoir on seepage capacity by means of the pore analysis technology of artificial intelligence HSV color space.The development degree of dissolution pores and intergrandular pores has an important impact on the reservoir permeability.(3)The porethroat structuredevelopment in the Mishrif Formation reservoirs was controlled by the sedimentation,diagenesis and rock type.and the combination characteristics of porethroat structures of carbonate rocks with different physical properties and sedimentary microphasics is different.According to the characterization of pore-throat structure,it is considered that the interlayers’ development is closely related to sea level change and/or high-frequency rotation,which provides a theoretical foundation for studying the distribution feature of underground anomalous infiltration body and its influence on fluid flow and is conducive to the formulation of the exploitation optimization strategy of the H oilfield.