Ann: Hydrocarbon gas recovered & evaluation program forward plan, page-590

Invictus has reported that they do not believe the Pebbly Arkose has closure, which I interpret to mean they do not think the faults are sealing in the Pebbly Arkose. However, we have not received a technical report containing the results of petrophysical analysis, cuttings analysis, sidewall core analysis and MDT pressure data etc. so that we can disseminate the data and reach our own conclusions.

A gas sample has been extracted from the Pebbly Arkose, but we were told the gas was at residual saturation. However, from my experience, the effect of illite clay material within the matrix could cause the log analyst to misinterpret the deep resistivity measurements because the presence of illite makes the sands appear water bearing, yet the sands are capable of flowing hydrocarbons during the flow test (DST). The following is an extract from Oesterlen and Millsteed's 1994 paper: "The matrix is either a calcite spar cement or is clay-rich, being mainly kaolinite and illite, or rarely smectite". Kaolinite does not affect the resistivity measurements, but illite will. Smectite has a much greater effect than illite in reducing resistivity, but its occurrence is expected to be low.

I wonder if Invictus has looked into this aspect? Have they detected illite in the cuttings? Are there preliminary sidewall core clay content results from M-1 (although formation damage expected)? What other evidence do they have to conclude that the faults in the Pebbly Arkose have caused the gas to migrate elsewhere? Did the MDT show evidence of depeted pressure?

At least 10 days was spent attempting to retrieve a gas/oil sample via TLC, but to no avail. I would like to read an account of the logging activities on each of those days. Apparently, the CFA from the MDT on wireline indicated gas condensate, however, unfortunately, no sample was collected because they had to POOH due to differential sticking of the wireline cable. TLC is less prone to sticking, so what were the reasons for not even collecting one sample?

I would like to be proved wrong, but attempting wireline MDT in M-2ST is not something I would advise doing. The sidetrack well profile will not be vertical, so the cable might stick again and even if the mud weight is lower than in M-2. there is still a risk of diff sticking over the higher perm zones in the Upper Angwa. Based on my experience with difficult wells such as these, the best options is to run the liner rather than perform a sidetrack (provided the hole has not bridged or collapsed), and much of the reservoir engineering data can be derived from well test analysis. There is also a cased hole MDT equivalent- far better than the planned sidetrack.