As it is usual in Oil reservoir modelling, it seem you have a very dense geophysical information (may be acoustic impedance) and low dense information from wells.
In these case is natural that the best result are obtained from collocated cokriging, similar result can be obtained from kriging with external drift and the homologous in the simulation scope. I think that 14 pint is to short for correct variogram modelling, and it is recommendable to use cross variogram in collocate cokriging. A solution for know the shape of the variogram could be using the background information, if it is close correlate to the wells information, bat I´m not sure that it is a good solution. Form more help please be more specific King regards Adrian Martínez Vargas Instituto Superior Minero Metalúrgico. Moa Holguín Cuba. CP 83329 ----- Original Message ----- From: Tomislav Malvic RGNF To: [EMAIL PROTECTED] Sent: Friday, November 15, 2002 2:24 PM Subject: AI-GEOSTATS: Kriging versus inv. Dist. Weighting Dear all, This is my first try at geostat mailing list, and maybe my question will not be very "professional". I work with data set of porosity in one oil reservoir. Interpolations were done with three interpolation methods: Inverse distance weighting, Kriging (ordinary) and Cokriging (collocated). I done spatial analysis with semivariogram modelling for (co)Kriging. After all, I calculated true error for every included point as difference between real value and estimated value at the same place. I was confused when I saw that Kriging error was higher of Inverse Distance Weighting error! The lowest errors were gained by Cokriging (with the same semivariogram modell as used in Kriging). What could be reason for that? Maybe 14 points is too low set for proper modelling of directional semivariogram analysis (directions=0 and 90 degrees). I tested several lag distances and distance with the highest range was chosen. If chosen distance is too low interpolation map contains mostly areas of "bull-eyes". Also, input points are moderately clustered. Thank you and best regards, Tomislav -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
