Fine Characterization of Fractures and Secondary Dissolution in Reef-Shoal Limestone Reservoirs Based on LWD Resistivity Imaging Logging Analysis—A Case Study of Lufeng Oilfield in the Pearl River Mouth Basin

GAO Yongming; HE Lipeng; QU Changwei; LI Shenzhuan; WU Jinlong

doi:10.13512/j.hndz.2024.02.10

Abstract：Lufeng X-1 oilfield is a high-quality reef-shoal limestone oilfield discovered during exploration in the eastern Pearl River Mouth Basin in recent years.Abundant oil and gas resources are discovered in this oilfield,but the limestone reservoir is characterized by complex lithology,complex pore structure,and strong heterogeneity,which bring great challenges to reservoir evaluation and overall oilfield development.In this paper,high-resolution LWD(Logging While Drilling)resistivity imaging logging technology was utilized to study the sedimentary environment analysis,fine characterization of fractures,quantitative calculation of secondary dissolution,and main controlling factors of productivity of reef-shoal limestone.The results show that the Lufeng X-1 limestone oil layer can be subdivided vertically into ZJ10A and ZJ10B limestone sections.The ZJ10A limestone section mainly develops reef limestone with the texture of massive bedding and laminated bedding.The ZJ10B limestone section was mainly deposited in bioclastic beach environments,with the sedimentary texture of laminated bedding.Based on high-resolution resistivity imaging data,it is determined that the ZJ10A limestone section mainly develops high-angle structural fractures,with good fracture effectiveness and vertical communication.Dissolved fractures and isolated fractures are developed in ZJ10B limestone section,with poor fracture effectiveness and vertical communication.Various secondary dissolution types are developed in Lufeng X-1 oilfield,including mottled,lumpy,honeycomb and bedding dissolution.The resistivity spectrum analysis method and PoroTex method are used to quantitatively calculate dissolution porosity and apparent porosity,showing that secondary dissolution porosity and apparent porosity were both relatively high in the high-quality reservoir section.Combined resistivity imaging logging interpretation results and dynamic production data,main factors controlling the productivity of the Lufeng X-1 limestone oil layer were comprehensively analyzed.Secondary dissolution contributes positively to productivity,while high-angle structural fractures contribute negatively.The successful application of high-resolution imaging logging technology in the reef-shoal limestone section of the Lufeng X-1 oilfield not only meets the needs for fine reservoir characterization,but also provides a solid data foundation for the subsequent overall development of the Lufeng X-1 oilfield.