Ann: Strong Gas Shows in Multiple Upper & Lower Angwa Reservoirs, page-381

Used ChatGPT to help answer get insight after writing this. Know I could have done this at the start but it's a bloody AI software and not experienced industry experts

1.

Yes, while gas readings are commonly obtained using a gas trap at the flowline near the shale shakers, as you mentioned, identifying oil directly in the returning mud is a bit more challenging, especially if the mud system being used is water-based. Here are some points to consider:

Mud Logging for Oil Shows: Mud loggers routinely monitor the returning mud for "oil shows." Indications of oil in the mud can include an oily sheen on the mud pit surface or on cuttings, staining of cuttings, or even fluorescence when exposed to UV light (this depends on the type of oil). These observations provide qualitative information rather than quantitative.

Water-Based Mud and Oil Interaction: If you're using a water-based mud system, oil from the formation will not mix homogeneously with the mud, making it easier to spot the aforementioned "oil shows." This is in contrast to an oil-based mud system, where it's much harder to discern any additional oil.

Dilution Factor: Any oil entering the mud system from the formation would be heavily diluted by the volume of drilling mud in circulation. So, while there might be signs of oil presence, determining the exact volume or quantifying it would be difficult.

Challenges in Quantification: While gas can be extracted from the mud and quantified with relative ease using gas chromatographs or mass spectrometers, quantifying minute amounts of oil in a water-based mud system is more challenging. Direct quantification would require specialized equipment and may not be feasible on a standard drilling rig in real-time.

Market Declarations: You're right in suggesting that even if there are signs of oil, it might not be substantial enough for a company to declare to the market. Market declarations usually rely on more definitive tests and evaluations, such as well testing or wireline logging, to ascertain the potential commercial viability of an oil discovery.

2.

Your understanding is correct. As you move up the carbon chain beyond C5 (pentane), you start entering the territory of liquids at surface conditions, and these heavier hydrocarbons won't be efficiently captured by the gas-detection system associated with the mud logs.

Here's a bit more detail:

• Gas Detection Systems: Most gas detectors in mud logging units, which are typically connected near the shale shakers, are designed to detect gases coming out of the mud. They work efficiently for methane (C1) up to pentane (C5) because these hydrocarbons are in a gaseous state at surface conditions. But as you correctly pointed out, hydrocarbons like octane (C8) or decane (C10) are liquid at surface conditions and won't be efficiently captured by these systems.

• Mud Logging for Heavier Hydrocarbons: While the gas detector may not capture the heavier hydrocarbons, the mud loggers should still be on the lookout for any signs of liquid hydrocarbons in the cuttings or the mud itself. This can be observed as an oil sheen, fluorescence under UV light, or direct visual identification of liquid hydrocarbon droplets. However, quantifying the amount of these heavier hydrocarbons based on these observations can be challenging.