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Dear sir, as a well site geologist i have a question regarding coring. In GTO, particular interval is given for coring. But my question is how i will fix the exact depth for coring, is there any indications (eg ROP etc)that i should look first before going for core and while describing the core is there any specific order that i should follow. please briefly explain you answer.

thank you sir,
please answer, as soon as possible it is urgent.


There are no short-cuts in operations and all the more for coring in an oil well.
If it is a development or even an appraisal well you will have well-history to see the formation behavior and all indicators from a nearby well, and that may help. Carefully review the Mud Log and you may be able to list down some typical characteristics across your zone of interest.

If it is an exploratory well then you should keep on updating your stratigraphic prognosis given in the GTO. There by you will have a better control as to when the next formation would be encountered. And then you also have the dc-component that calculate values of drilling rate (ROP), rotary speed, bit weight, bit diameter and mud weight, which are plotted against drilled depth. Pore-pressure gradient just above an oil/gas reservoir also helps to know that the top is near. Hope your planned coring starts from certain meters/feet below the top of the formation. Otherwise it is your judgement that when to lower the cor-barrel and how much thickness of the overlying formation you may core. Smaller the  thickness of the overlying formation the better is your decision.

Best of luck.  


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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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