Abstract

The Abo and Drinkard units of the West Dollarhide Field, Lea Co., NM were deposited on the western flanks of the Central Basin Platform, during lower Leonardian time. The reservoir rocks consist of a range of lithologies, from a completely dolomitized mud-stone facies to non-dolomitized packstone-grainstone intervals. In order to determine whether the flow units are controlled by depositional cycles or diagenetic processes, a detailed reservoir model is needed.

To date, petrologists and petrographers have used various charts, either published standards or their own developed method, to log core by hand. This produces a variety of detailed and accurate descriptions, but is not of any direct use to a petroleum engineer for reservoir computer in a pictorial format. RAGCORE^© allows a petrographer to directly enter by-eye descriptions into a computer in a pictorial format. RAGCORE^© was initially written by R. Graham (of RAGWARE, Inc.) as a part of RAGWARE^©, which is a composite geologic log system. However, the current study has customized RAGCORE^© as a stand-alone module for use in carbonate (or siliclastic) core description. The main difference between this method and the standard hand format is that the pictorial data can be easily translated to a numerical spreadsheet format. In addition, if petrophysical logs are available in LAS format, these can be displayed with the core description.

No other program on the market has these capabilities. All the pictorial lithologies have a numerical code, in the spreadsheet, which is keyed to the pictorial printout. This program is not a static data entry program. However, it is necessary to have completed the descriptive data entry before transporting the data to the spreadsheet. Changes that are made in the spreadsheet, and are to be duplicated in RAGCORE^©, must be done manually. Before transporting data to the spreadsheet, it is possible to go back to the pictorial log and modify the previously entered data, as thin-section and SEM analyses are completed.

As currently set, there are 17 main data entry groups in RAGCORE^©: Lithology, Main Facies (modified Dunham classification), Facies Modifier, Bedding, Bedding Contacts, Sedimentary Structures, Stratigraphic Accessories, Fossils, Dolomite Crystal Size, Calcite Crystal Size, Anhydrite Type (cement/replacive), Grain Sizes, Depositional Sorting, Grain Roundness, Porosity Type, Shows and Remarks (descriptive text). Within these groups are various symbols, referred to as objects in the program, which are specific to each group. For example, in the lithology group the objects are further descriptive breakdowns of the lithology, such as anhydritic limy-dolomite or dolomitic lime.

These data are used to describe the core by individual petrophysical units. A petrophysical unit is defined as a section of core in which the descriptive properties, especially those affecting fluid flow, do not change. A petrophysical unit ranges from inches to greater than a foot in thickness.

When the data is transferred into the spreadsheet format it can be further analyzed in the spreadsheet to determine flow units. By cross-referencing the pictorial print-out with the spreadsheet analysis it is easier to correlate between wells and determine whether the flow-units are controlled by depositional or diagenetic processes. Eventually the spreadsheet data can also be passed on to a reservoir engineer to aid with reservoir simulation models.