Geology/Follow up question about well site fluorescence evaluation.
QUESTION: Dear Sir,
Thanks for last answer for differentiating fluorescence of sample from oil based mud. Also I would like to ask that is there any reliable equipment that are used at well site in mudlogging unit to identify whether the oil show is from reservior or from oil based mud.
Another question is that what are the main parameter to be monitored during coring operation. What is the main QC required for coring job.
Thanking you in advance.
With warm regards
ANSWER: Dear Rahul,
Thanks for your interest and sending me new question.
Adding to my previous answer, please note that wellsite mudlogging unit almost all are equipped with Total Gas Detector (TGD) and Chromatograph which are very useful instruments for hydrocarbon detection. Once drilling starts with oil based mud you will observe the increased total gas readings on TGD and their compositional break up on the Chromatograph from C1, C2, C3, ic4, nC4, and C5. (Methan, Ethane, Propane iso Butan,N-butance and Pentane). Through the time lighter component of gasses (c1-c3) will start to circulate out and their readings will gradually decrease to low level. So you get to keep the record of the changing baseline from higher gas values to lower gas values on TGD and Chromatograph charts. Formation gas if enters through the well bore a kick from the gas baseline will be recorded on both instruments with significantly higher C1 values than before and after few minutes the increased C1 values will try to catch up the previous baseline and itís also possible kicks would start increasing after first kick and followed by another kicks or cycles. Anything above the baseline should be considered as change of the fluid system either the source of the new event is from formation or addition has made in oil in circulation system from surface. (Keep checking from mud engineer and floor man about any additional chemical or oil addition in mud system)
The fundamental quality control for coring is the core point selection which is the key decision as nobody likes to take a core in wrong lithology for wasting precious time and hell lot of money. Therefore, it needs to be ensured the right lithology before pulling out of hole and running core barrel in. Drill few feet inside the desired lithology and after confirming when it bottoms up and only then run core barrel. While coring monitoring of rate of penetration, gas detection and lithology examination are essential. Though, very little amount of rock cutting comes out of hole but whatever comes to the surface should be examined. Once coring operations completes every care should be taken to collect and preserve the core out of core barrel and marked depths properly on the core boxes. Few chips should be cut from the core on every foot or so for quick examination and interpretation
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QUESTION: Dear Sir,
Thanks for the reply.
If we are drilling exploratory well which LWD tools you would recommend to use to identify zone of interest of coring.
Thanks and regards
The LWD too can take several measurements including natural Gamma Ray, Spectral Gamma Ray, Electrical resistivity, Density and Neutorn. Gamma Ray is the best tool to identify the lithology and I would recommend to observe closely the GR response while taking core decision followed by sample examination and description at the well site.
Hope this answer helps.
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