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QUESTION: Dear Sir, while drilling a well at a depth of 2600m we got claystone with white to be precise milky white, soft, cuttings. i thought that they may be siltstone but while seeing the grain size it is mostly clayey in nature. can you please tell me which rock it could be. And one more doubt how to differentiate Marl and Kalonitic clay in cuttings.

Thank you and have a nice day
Ali Mohammed Dar


I will try to reply only the second part of your question. Marl is a mixture of clastic and calcareous contents, where as the kaolinitic clay is anticipated to be dominantly clastic.The clay cuttings would be plastic and smooth in nature, while the marls generally do not form good shaped cuttings, have relatively larger grain size and also have a higher solubility in acidic fluid due to the higher calcareous content.  An acid would help in differentiating between clay and a marl. A clay with high calcareous content may also fall in the category of a marl.

---------- FOLLOW-UP ----------

QUESTION: Thanks sir for your time bound response, one more question is,
Can you please tell me the significance of determining constant salinity while reverse out or subduing the well.

with regards
Ali MOhammed


Sorry, I am not a drilling expert. However, logically it needs to be done just to keep a check that no changes are taking place in the original composition and consistency of the mud, which also includes monitoring the volume of returns in the mud-pit. You may appreciate that any change would indicate something happening within the well e.g. loss, gain and depending upon the salinity of the formation water the salinity would change in either way.
You may contact a drilling expert too.


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Nusrat Kamal Siddiqui (Mr)


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.


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

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.

-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.

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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