The 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
Many decisions in enhanced oil recovery (EOR) pilot design are required to plan an EOR pilot that, if executed successfully, gives a reliable data set and sufficient information to make full field EOR development decisions in the future. A miscible gas EOR pilot was designed for the formation "X" in the field "Y" of Kuwait using an uncertainty driven approach.
The method presented in this is paper is a qualitative way of linking key miscible gas EOR performance parameters of the formation to the intrinsic uncertainties of the properties impacting them. An assessment of the impact of the uncertainty itself, likelihood of impact and the acceptance, or required uncertainty reduction, provided the direct link to the selection of the pilot concept, the pilot type, the pilot location and the operational sequence of executing the pilot.
The key miscible EOR performance drivers for the formation in, with unacceptable high uncertainty, are vertical sweep efficiency (Ev) and remaining oil saturation (ROS). Hence it was decided a non-producing pilot with a single injection well and with observation well(s), is the EOR pilot concept and type enabling data gathering to address the above key uncertainties. The pilot area and pilot location was assessed via a semi-quantitative assessment of more than 10 parameters impacting miscible gas injection EOR, for example remaining oil, recovery factor, and pilot location distance to producers. While the final goal of the miscible gas EOR development for the formation is a miscible CO2 flood, it was decided to use produced hydrocarbon (HC) gas as a pilot injectant. This addresses the key objectives of the pilot with sufficient accuracy, while avoiding costly and timeline infrastructure changes at this early stage of understanding the chances of a successful EOR development.
The additive information to the audience is the consistent approach of using an uncertainty based assessment of key EOR performance drivers throughout the entire pilot planning steps and defining pilot objectives, pilot concept and type as well as pilot location.
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