oa Formation evaluation in Palaeozoic gas reservoirs of the South Rub’ Al-Khali Basin, Saudi Arabia

Acquiring accurate subsurface data forms a key objective for the South Rub Al-Khali Company in its currently ongoing exploration drilling campaign in the remote and challenging environment of the South Rub’ Al-Khali Desert. Exploring for non-associated gas in Paleozoic formations brings significant well data gathering challenges. These include logistics and planning, hole conditions, depths and associated temperatures and pressures. The combination of often poor reservoir properties and deep invasion can result in impaired reservoirs that cannot be sampled or tested with conclusive results. In order to maximise the chance of obtaining a petrophysical evaluation with conclusive results in terms of reservoir quality and fluid content, an extensive dataset has been acquired during the exploration campaign. The data set comprises cores, ditch cuttings, compositional analysis of the various gas show components, and surface sampling of any shows. Petrophysical data include logging-while-drilling data, open-hole electric wireline<br>logs, pressure measurements, sampling and multiple offset VSP’s. Data obtained while drilling was repeated on electric wireline to spot invasion effects as a result of the mud system used. The presentation will focus on the data gathering strategy and planning and how this has been catered for in the well design. Lessons from the first well were captured in a structured review process leading to cost savings in subsequent wells without impacting the quality of the dataset acquired. Integration of the extensive data acquired has lead to a better understanding of the various play elements resulting in a robust risking of all exploration prospects.