Think for yourself with questions like these on Dr M's Petrophysics Courses Public Courses annually in Kuala Lumpur, Vienna and Dubai. In-House by request The evaluation's required value of n: The value of n is determined by the n definition plot, commonly seen in core analysis reports, such that n is the negative slope of Log(Sw) vs. Log(Rt/Ro). This plot is conventionally populated by core data, with its numerous shortcomings, notably that Rt/Ro is not the log data's Rt/Ro which will actually be used in the evaluation. This n definition plot can be used more effectively if we..
A value for mixed wettability n: Many oil reservoirs have mixed wettabilities. These will have Sw's below those implied from conventionally cleaned, strongly water wet, capillary pressure Sw-Ht data. If we reverse calculate n from these high capillary pressure Sw's using log data, n will be high: we shall be assuming a higher Sw for a given resistivity. Conversely, the conventionally cleaned, strongly water wet special core analysis electrical n values on the same plugs may be low: water wet systems have low n's, n will be low. These two simple observations provide a means to constrain n and largely overcome your worries in mixed wet reservoirs. This information is probably sitting quietly behind you on your shelf, right now. Can you hear it?
At last, a cut-off you can justify! Have you or your friendly petrophysicist ever used relative permeability data to determine a value for your oil reservoir's netpay cut-off? No? But relative permeability data defines the conditions at which oil becomes mobile … at which an oil saturated rock becomes PAY.
Think "Pore throat size distribution controls Sw AND k, so therefore.." k and Sw are both controlled by pore throat size. Porosity and NMR T2 distributions are not (surface area). Does your company use Sw or Ø*Sh's stronger correlation with k to predict k? We pay for NMR logging, core analysis "flow zones" and “rock types” in attempts to address k variations with porosity.. but we often don’t need to. Sometimes we just need to look at what we already have for a cheaper, more powerful correlation of log analysis results with k.. (Reason: Service companies can’t make money out of data that already exists.. that is the task of the Interested Petrophysicist)
The evaluation's required value of m: The objective of m is to convert the evaluation’s Ø, with a*Rw, into the evaluation’s Ro (water saturated formation resistivity), not core analysis Ro! The laboratory is an inadequate analogy of in-situ conditions - witness the 100’s of learned papers telling us so, the latest tranche informing us that electrical anisotropy further invalidates our core data a and m’s. With certain water zones (Sw100 zones from side-walls, cuttings and chromatograph), spanning a range of Ø in rocks of the same pore-type (similar Ø-k xplots) why do we choose to ignore Nature’s own reservoir conditions m laboratory and worry instead about reservoir to laboratory inequalities? This particular faith in core data is misconceived.. m must predict the log data’s Ro, the lab data’s Ro is irrelevant and can be misleading. Once again.. the lab data’s Ro can be misleading. Think for yourself - focus on the data that will actually be used in the evaluation. (Reason: Service companies can’t make money out data that already exists.. that is the task of the Interested Petrophysicist)
A Passive "Comparison with" or an Active "Calibrate to"? What does the experienced petrophysicist intuitively use as criteria for the reservoir Data Hierarchy, that is ranking data for its usefulness? This petrophysicist suggests Directness, Accuracy and Spatial Definition are the root criteria of experienced staff. How do we navigate through competing data sets and methods? Experienced petrophysicists, geologists and engineers: What do you use? Analyse That!
Do we really need FFV for Permeability ? The PPL method does not require a log of Free Fluid Volume (FFV) or Log Mean T2 to solve for permeability. This is advantageous during logging operations because it avoids the need to log the far more problematic FFV with an NMR tool - for example FFV cannot easily be obtained in gas zones and logging is often slowed dramatically to an expensive crawl in the belief that the full T2 spectrum must be logged to achieve useful NMR results. Not so. Bound Fluid Volume (BFV) is the easiest and fastest log to obtain with an NMR tool. It is 100% water, rapidly polarizes and is rapidly counted in early T2 time. With this, a robust and accurate permeability is achieved by the PPL approach, in clastics and non-vuggy carbonates. Whilst service companies may be aware of how this can be achieved it usually is not in their interests to advance such an approach. Why, because service companies make money from running logs, not from evaluating your reservoir. Indeed, many wells can be accurately evaluated for permeability without even acquiring NMR data, set your "Interested Petrophysicist" to work on that one.. The message of many of these asides and of my 25 years experience in mainstream petrophysics is that service companies have excellent and clever staff but, they are NOT MOTIVATED to evaluate your reservoir - they are motivated to create data. It's more profitable. It is the chosen niche of PPL, from PhD to present, not to create data, but to extract the most from the data we already have. See also www.petrophysics.net/quotes.htm Email you own comments on our petrophysical world Training Options Summary View 10 Reasons View Testimonials Public Course Schedule Get Course Manual Register for a Public Course In-House Course Enquiry Flyer |