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Geology/Log interpretation

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Question
Dear Sir,

Is it possible to differentiate on wireline log, cratonic derived sediment deposit in early to middle Jurassic and volcanic arc derived sediment deposit in late Jurassic.

Early to middle Jurassic sediment transported from west to east and provenance is craton

Later jurassic sediment derived from east to west form volcanic arc.

This come from the geology of area, but how can I validate this on well section

available data only wireline log SP, GR, LLD, LLS DT, RHOB, Nphi.

Answer
Irfan,
A difficult question. To identify litology, age of sediments and to mark the contact on logs, we just can' t rely on one source of information. It has to be a combination of perography of ditch-cuttings, fossil content of cuttings and keeping in mind the geological history. Whatever may be the source and direction of the sediment supply it is brought by water where life develops. Do you have an idea of the fossil content? The distance of provenance to the eventual place of deposition will have an effect on the size and roundness of the grains. I understand that the craton (shield) in the west does not have platform deposits, and the shield areas are normally composed of metamorphic rocks, which normally have excessive micas. Do you have the results of the lithological content of the shield? Any dominant mineral which may not be present in material sourced from the east?
For normal suite of logs the sedimentary rocks are either clastics or carbonates and their different type of lithologies. The NGS, however, can differentiate between the radioactivity emission for different minerals. So if there is the knowledge of what type of radio active minerals are in the two source areas then you may be able to identify the contact on logs. The GR you have may be of help if there is a marked difference in the total emission. Similarly, check for the heavy mineral content of the two areas. Any difference will be of help too.
Hence, it is a combination of all the above analyses that may allow you to differentite in a plausible manner the two sediment supplies.
Seismic stratigraphy may also help you to mark the regional contact, as it will tell about the direction of sediment supply. Place your well logs on the interpreted seismic section to get an idea, and then fine-tune the contact on logs. See the Mudlog if it shows presence of volcanic debri.

Think beyond logs to get more ideas. Hope it helps.

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Nusrat Kamal Siddiqui (Mr)

Expertise

I am a petroleum exploration geologist with about 40+ years of diversified experience. I can answer questions on stratigraphy, log interpretation, field studies based on set of logs and core results, general geology etc. Can provide guidance for career planning in earth sciences. Can not help in questions about hard rocks, igneous petrology & mineralogy, sequence stratigraphy and seismic.

Experience

Petroleum Exploration - field geology, stratigraphy, prospect generation, interpretation of satellite imagery (visual), log interpretation.

Organizations
Retired in May, 2006 as Senior Manager Exploration from Pakistan Petroleum Limited after serving 26 years. Since then continuing in active service with petroleum exploration companies.A cumulative experience of about 40 years covers 30 years in petroleum exploration, 5 years hydrogeology experience in Libya, and about 5 years of dam geology in Pakistan.

Publications
-AAPG Bulletin (Vol.88, July, 2004); paper on Sui Main Limestone (Eocene), a prolific gas reservoir in Pakistan. -Have presented papers on diversified topics ranging from spirituality, flood control, remote sensing and off course geology in France, Nepal, Bangladesh, Sri Lanka, UAE, Kashmir, India and Pakistan that have been published in respective Special Proceedings. -ONGC Bulletin(India) Vol. 44, Number 2, December, 2009; Chapter 19.A & 19.B on basin architecture and stratigraphy of Pakistan, p.402-474.

Education/Credentials
BSc Honours in Geology and Master of Science in Petroleum and Structural Geology. PGD from ITC, The Netherlands.

Awards and Honors
-Remained Active Member of AAPG from 1990-2006; founding member of PAPG (a local affiliate of AAPG). -Life member of SEGMITE & AGID, and Senior Editor of SEGMITE magazine. -Member of the Board of Studies, i. Department of Petroleum & Gas Engineering (BUITMS, Quetta), and ii. Geology Department, Sindh University, Jamshoro. -Member of Stratigraphic Committee of Pakistan. -Represented Mining Journal, UK in Pakistan till 2007. -Chairman of Annual Technical Conference (ATC)& Oil Show, an SPE/PAPG annual event, in 2003. -Chairman Technical Committee (ATC, 2002).

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