Abstract
It was showed that reservoir diagenetic and reservoir-forming characteristics are of great value for exploration and exploitation of conventional and unconventional reservoirs. Thus understanding on diagenetic evolution has important significance for successful hydrocarbon exploration. In this paper, a process-based model (PBM) was established to give quantitative characterization of diagenesis strength and its corresponding effect on porosity evolution in burial history on identifying of diagenetic sequence. Taking the Paleogene lake sediment sandstone in Bozhong depression as an example, diagenetic sequences as well as occurrence stage of each diagenesis including compaction (MC), cementation (CEM), and dissolution (DIS) were determined by means of thin section, scanning electron microscope, homogenization temperature of fluid inclusion, and then diagenesis type, diagenesis strength and its effect on porosity in burial history were identified based on diagenetic numerical model proposed in this research. The main understandings are as follows: (i) The lithofacies for the Ed1, Ed2, Ed3, and Es1 in the Paleogene lake sandstone are Q63.8F22.2L14.0, Q32.0F38.9L29.1, Q28.8F59.5L12.5, and Q47.1F16.9L36.0, respectively; (ii) the reservoir of Paleogene in Bozhong sag is mainly in stage IB‒IIB. It was showed that 1600‒2100 m is in the stage IB, while 2000‒3100 m is in the stage IIA1, 3000‒4000 m is in the stage IIA1, and over 4000 m is in IIB; (iii) The diagenesis experienced by these sandstones includes compaction/carbonate cementation-feldspar dissolution/carbonate dissolution/precipitation of quartz cements and kaolin-illitization of kaoline/illite/precipitation of ferrocalcite and ankerite; (iv) The influence of diagenesis on pore development of the sandstone reservoir in the study area was discussed. The effects of diagenesis on pore development were quantitatively described by compaction, cementation and dissolution, and the effects of diagenesis on pore development were analyzed.
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