Fracture Characterization and Modelling of Shale Formations in Miri, Sarawak

Abstract

Studies on fractured reservoir is becoming vital especially in shale formation due to the emerging of production for shale oil and gas globally, besides awareness of disasters due to incorrect estimation of subsurface overpressure and fracture pressure. Understanding the formation of fracture in relation to the structural evolution and its behavior in various lithofacies is important. Another major factor controlling the fracture development beside lithology and mineral composition, is abnormal pressure. Therefore, a study on fracture characterization and modelling of shale formations is still ongoing to characterize shale by evaluating lithofacies and fracture characteristics. In addition, analysis of subsurface rock properties to determine the fracture gradient in shales of gas wells and fracture models of selected shale formations are in progress. In these research, the study of fractures will be determined both by onshore and offshore data. In the onshore scale, the natural fracture will be evaluated, taking into account the natural fractures network data includes contribution of mineral composition and lithofacies in Miri region. While, offshore data will be analyzed through well log data and initial relationships of Eaton’s method in estimating fracture pressure along the wellbore. Outcrop studies was conducted around Miri vicinity mainly at Beluru and Long Lama route. Lithofacies identification was determined through X-ray diffraction (XRD), X-ray Fluorescence (XRF) and total organic carbon (TOC). Eminently, based on the XRD and XRF analysis, there are two types of shale identified; where the shale with high quartz percentage is classified as siliceous black shale and located nearby Long Lama whereas those with prominent calcite percentage is categorized as calcareous grey shale, which are found in the Beluru. In general, the type of shales around study area is referred as grey shale with good level of fracture development. The range of TOC percentages of the samples are from 2.03 to 2.28. Therefore, the result obtained from integration of well log analysis and fracture gradient prediction can be compared with natural fracture model in West Baram Delta.