ASSESSING SEDIMENTOLOGICAL AND DIAGENETIC CONTROLS ON RESERVOIR QUALITY OF THE FLUVIO-DELTAIC MIOCENE SURMA GROUP DEPOSITS BASED ON CORE SAMPLE ANALYSIS OF FENCHUGANJ WELL 02

The Miocene aged fluvio-deltaic Surma Group sandstones are the prime gas producing zone in Bangladesh and the study of this gas producing zone is a must as the country is going for extensive drilling and exploration to meet the energy demand of the population. However, there has not been enough study based on the core samples analysis from the reservoir sandstones. Therefore, this present study has aimed to analyze the sedimentological, petrographic and diagenetic controls on the reservoir quality of the Surma Group sandstones from the north-eastern part of the Bengal Basin. The specific objectives that have been achieved from this study are: i) grain size, texture, rock type analyses of the samples in hand specimen, ii) petrographic thin sections, scanning electron microscopy(SEM) and X-ray Diffraction(XRD) images analyses, iii) porosity-permeability determination of the samples, iv) depositional and diagenetic controls study on the reservoir quality. 16 core samples of the Fenchuganj Gas Field were collected from the core division of Bangladesh Petroleum Exploration and Production Company Limited (BAPEX) and sent in lab to prepare petrographic thin sections, SEM and XRD imaging. Hand specimen analysis has revealed that most of the samples are fine to medium grained sand with some shale. Petrographic studies have confirmed the composition of the sandstones as well as the presence of bended and squashed minerals which represent that mechanical compaction has played a major role in the porosity-permeability reduction. On the other hand, the presence of corroded grains represents the dissolution of the minerals that have created secondary porosity. Scanning Electron Microscopy and X-Ray diffraction analyses have suggested the presence of quartz overgrowth, kaolinite, and Chlorite clay minerals. The presence of clay minerals has slightly reduced the porosity and permeability. The present study demonstrates that depositional environment and diagenesis play an important role in the reservoir quality of the Surma Group deposits which need to be understood for successful exploration.