Well Logging and Formation Evaluation Challenges in the Deepest Well in the Sultanate of Oman (HPHT Tight Sand Reservoirs)

Abstract

AbstractThe high demand for natural gas in Oman has stimulated new exploration for gas resources that can be developed commercially. The Exploration Directorate in Petroleum Development Oman (PDO) has recently extended its exploration programme into the deeper parts of the sedimentary basins in North Oman. Reservoirs located here, principally in the Amin and Nimr formations, are expected to be tight (low porosity and permeability).Data acquisition and petrophysical evaluation are major challenges when exploring the deep gas plays in North Oman. This is due to the hostile reservoir environment, i.e. high pressure and high temperature (HPHT). Current logging tools (wireline, LWD) are rated for operations up to 175°C and 20,000 psi. Data acquisition becomes significantly challenging as higher temperatures cause the logging tool electronics to fail.This paper describes data acquisition and formation evaluation challenges for the deepest gas well drilled to date in the Fahud Salt Basin in the Sultanate of Oman. The first part of the paper discusses the logging plans, challenges and how, through optimised data acquisition, the objectives of logging programmes have been met. The planning phase started six months prior to well spud to manage the high uncertainty in the prognosed well TD depth and borehole temperature. The final well depth reached was 7145 m AH which is currently Oman’s deepest well. The maximum recorded downhole temperature was 195°C which posed a serious risk to successfully logging the last borehole section. Both LWD and wireline options were implemented and are discussed in the paper. Dual density tools were successfully used to overcome the borehole breakouts whereas flask Resistivity and HPHT tools were used to overcome borehole temperature limitations.The second part of the paper describes formation evaluation methodologies we used in tight reservoirs. Improved porosity and water saturation calculations by integrating data from well logs, drilling, mud logging as well as geochemistry are discussed