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Geology/best lithology for casing point


QUESTION: please no the lithologies for casing point?

ANSWER: Muhammad,

Any hard lithology (limestone, sandstone) and even compact shale can serve as a good casing point. For production casing you have to be as close to the top of the reservoir as possible, any way. Sometimes top of a reservoir consists of a transition zone, which provides a perfect casing point. Sui Main Limestone (SML) in Pakistan is one such prolific gas reservoir.
You may go through my paper on SML published in AAPG Bulletin, July, 2004.

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QUESTION: If we have limestone,shale,claystone,sandstone,dolomite, then what will be the best order to case the well.(note: !:if we are not in reservoir zone?   @:if we are in reservoir zone?)

ANSWER: Muhammad,

The best order of priority would be sandstone, dolomite, limestone and shale (compact and not splintery). Never in a claystone.

In reservoir zone the production string shoe setting depends upon the behavior of the aquifer.

In a gas pool with volumetric expansion drive the aquifer influx is minimum. The SML in Sui Field is a typical case. We used to cement the shoe about 75 m above the Field GWC, and the perforations still higher.

In an active water-drive, may it be an oil pool or a gas pool, the decision is with the Reservoir department, and all the more for the deepest perforations.

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QUESTION: if there is a risk of complete loss in limestone then why not in clay stone?


Claystone is prone to getting mixed with water very quickly. Being at the casing shoe it creates a void below the shoe, which gets bigger with time. It endangers the integrity of the bond. The losses in a limestone can be cured, anyway, particularly if it is not a reservoir.
Whatever may be the case the claystone should never be an option.  


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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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