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Petrophysical Evaluation of Unconventional Lower Creataceous Shale Gas. A Case Study From Kuwait

Abstract

The exploratory efforts are focused on evaluation the unconventional Shale-oil/gas resources of Kuwait. This paper aims to present a petrophysical workflow involving interpretation of different datasets to evaluate the shale gas potential of the Early Cretaceous Makhul Formation. The Berriasian Lower Creataceous Makhul Formation is deposited regionally across Kuwait and other parts of the Arabian Gulf countries. It can be broadly sub-divided into three main zones: Basal Hot Shale, Middle and Upper Makhul Fm. The Basal Makhul Shale is black, organic-rich (kerogen), stained Lime mudstone and calcareous shales and has been established as a source rock for the Lower Cretaceous Petroleum system as well as unconventional reservoir. The middle and upper part of the Makhul has recorded numerous oil and gas shows during drilling. This Base Shale of Makhul formation was marked with considerable gas count in key wells and it was tested with positive results. Gives us a strong possibility of gas shale zone and identified as a potential shale oil play. Average thickness about 150 feet and characterized by very high Gamma due to the influence of Uranium and indicate considerable organic rich material (Kerogen), low matrix porosity, Ultra-low permeability, naturally fractured and highly over pressured in nature. Key to successfully completing shale gas/oil reservoirs is targeting intervals with good reservoir characters (porosity and hydrocarbon saturation) and organic richness. Natural fractures further enhance the reservoir properties. The major challenge for the organic rich reservoirs is the evaluation of actual porosity which by conventional analysis appears very high due to presence of the organic carbon. Other challenges are the accurate determination of the formation mineralogy. A clear cut workflow involving interpretation of different datasets has been evolved for identification and evaluation of this Shale Gas reservoir. Include the Integration of open-hole well log data, core porosity, core grain density, core TOC, XRD data, ECS and CMR logs. Corrected porosity from kerogen effect and calculate total organic carbon TOC from logs. It is recommended to acquire complete suite of advanced logs including ECS, CMR, UBI and core examination to properly evaluate the lithology, porosity, fractures and to determine Kerogen corrected effective porosity in organic rich formation.