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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

Early Palaeozoic-age non-associated gas fields operated by Petroleum Development Oman (PDO) in the Sultanate of Oman have traditionally comprised good reservoir quality sandstones located on three- or four-way dip-closed structural highs. While gas exploration success has continued over the last five years, this has been restricted to discoveries in much poorer quality ("tight") sandstone reservoirs. Significant challenges exist: target reservoirs are deep - over 4500 m (18,000 ft) with high reservoir temperatures (> 170°C). Porosities range from less than 3 to 10% with (ambient) permeabilities ranging from 0.001 to 1 mD. These tight reservoirs have elevated pressures (above hydrostatic) and many wells record GDT (Gas-Down-To) situations (i.e. no GWC recorded). Furthermore, basin modelling indicates that peak hydrocarbon generation occurred during the Palaeozoic and Mesozoic and may have continued until Early Tertiary times in some areas. A study was started in 2008 to analyse the above data applying a range of techniques including basin modelling, geochemistry, regional well results evaluation together with pressure data analysis and comparison with global analogues. This resulted in approval for a four well exploration campaign to evaluate diverse locations across north Oman addressing the quest for tight gas in a basin-centre setting. Drilling of the first exploration well started in late 2009 with the aim of proving the presence of deep gas accumulations and ultimately gain an indication of commercial attractiveness. This paper presents the key criteria expected to influence the deep gas play prospectivity (i.e. presence of favourable reservoir, hydrocarbon charge and retention) and the steps to mature this opportunity. We also highlight an approach to progressing an unconventional gas opportunity in a challenging geological environment, in the Middle East, where the maturation of this resource type is currently in its infancy.

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Well spacing is a key factor in the evaluation of pad economics for hydraulically fractured horizontal wells. The drilling at the wrong well spacing leads to either over-capitalization risk or leaving reserves in the ground both resulting in loss of net present value risk. This paper presents data acquisition techniques that aid in well interference identification and quantification. Integrated analysis of data from a well pad in the Vaca Muerta formation, including microseismic, chemical tracers, geochemical fingerprinting, and pressure measurement, indicates both pressure and production communication between the two wells studied. Then a dedicated interference test is designed and analyzed to provide insights on well spacing. The test consists of alternating shut-in periods of the two wells during which pressure and rate are closely monitored. Analytical and modeling work has quantified the degree of interference to be up to 20% on production rates. This interference test is performed between two ‘semi-confined’ wells. Future multi-well pads are planned to understand the production potential of a fully ‘confined’ well and the interference between neighboring wells, to further understand the well spacing and pad economics.

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