Electricity: measuring and testing – Particle precession resonance – Using well logging device
Reexamination Certificate
2001-04-06
2003-11-11
Arana, Louis (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Using well logging device
C702S008000
Reexamination Certificate
active
06646437
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to formation analysis and more particularly to identifying clay types and properties based on NMR porosity measurements using user-adjusted modeling parameters.
BACKGROUND OF THE INVENTION
The ability to differentiate between fluid types is one of the main concerns in the examination of the petrophysical properties of a geologic formation. For example, in the search for oil it is important to separate signals due to producible hydrocarbons from bound ones, as well as from the signal contribution of brine, which is a fluid phase of little interest. Extremely valuable is also the capability to distinguish among clay-bound water, capillary-bound water, movable water, gas, light oil, medium oil, and heavy oil.
In this regard, it is desirable to understand the structure and properties of the geological formation. A significant aid in this evaluation is the use of wireline logging and/or logging-while-drilling (LWD) measurements of the formation surrounding a borehole (referred to collectively as “logs” or “log measurements”). Typically, one or more logging tools are lowered into the borehole and the tool readings or measurement logs are recorded as the tools traverse the borehole. These measurement logs are used to infer the desired formation properties.
The hydrocarbon production potential of a subsurface formation is described in terms of a set of “petrophysical properties.” Such properties may include the lithology or the rock type, e.g., amount of sand, shale, limestone, or more detailed mineralogical description; the porosity or fraction of the rock that is void or pore space; the fluid saturations or fractions of the pore space occupied by oil, water and gas, and others. Wireline logging tools do not directly measure petrophysical properties, they measure “log properties”, for example, bulk density, electrical resistivity, acoustic velocity, or nuclear magnetic resonance (NMR) decay. Log properties are related to the petrophysical properties via mathematical or statistical relations, which are generally known in the art. In practice, frequently several different logging tools are combined and used simultaneously to obtain an integrated set of measurements. Thus, different tools may be used to obtain information about the same set of formation properties using different techniques, or different tools may be used to obtain information about different formation properties. In order to make optimal use of the measurement results from different tools, in practice their responses to known formations are modeled and, the model responses are compared to actual logs. The error signal generated in the process serves to improve the parameter estimates of the models and ultimately to provide an understanding of the petrophysical properties of the formation.
Several approaches have been proposed in the past to model the structure of geological formations, as well as the ability of different structures to retain fluids. Such models can be extremely valuable in practice. The present application discloses a new and improved nuclear magnetic resonance (NMR) porosity model using adsorbed water content in clay minerals. The proposed model can be used among other purposes for clay typing in formation evaluation.
NMR logging has proved very useful in formation evaluation. NMR logging tools known in the art include, for example, the centralized MRIL® tool made by NUMAR Corporation, a Halliburton company, and the sidewall CMR tool made by Schlumberger. The MRIL® tool is described, for example, in U.S. Pat. No. 4,710,713 to Taicher et al. and in various other publications including: “Spin Echo Magnetic Resonance Logging: Porosity and Free Fluid Index Determination,” by Miller, Paltiel, Gillen, Granot and Bouton, SPE 20561, 65th Annual Technical Conference of the SPE, New Orleans, La., Sep. 23-26, 1990; “Improved Log Quality With a Dual-Frequency Pulsed NMR Tool,” by Chandler, Drack, Miller and Prammer, SPE 28365, 69th Annual Technical Conference of the SPE, New Orleans, La., Sep. 25-28, 1994. Certain details of the structure and the use of the MRIL ® tool, as well as the interpretation of various measurement parameters are also discussed in U.S. Pat. Nos. 4,717,876; 4,717,877; 4,717,878; 5,212,447; 5,280,243; 5,309,098; 5,412,320; 5,517,115, 5,557,200; 5,696,448; 5,936,405, 6,005,389 and 6,023,164. The structure and operation of the Schlumberger CMR tool is described, for example, in U.S. Pat. Nos. 4,939,648; 5,055,787 and 5,055,788 and further in “Novel NMR Apparatus for Investigating an External Sample,” by Kleinberg, Sezginer and Griffin, J. Magn. Reson. 97, 466-485, 1992. The content of the above patents is hereby expressly incorporated by reference for all purposes, and all non-patent references are incorporated by reference for background.
Technology advances have made it possible to reduce the inter echo spacing of the downhole NMR logging tools such that these tools are able to measure very fast (for example, less than 1 ms) relaxing components of the subsurface rocks. See Prammer et.al., (1996). In most cases, these fast T
2
relaxation times are ascribed to the water bound in the clay mineral component of the rocks. As a result, the petroleum industry's interest in the application of NMR technology to aid in shaly sand evaluation has grown considerably. With reference to the list provided at the end of this section, useful prior art includes the publications by Prammer et. al., (1996); Allen et. al., (1998); Matteson et. al., 1998; Chitale et. al., (1999). However, until recently it remained unclear whether or not the water adsorbed on the clay surface (the so called clay-bound water in petrophysics) is detectable by NMR. This paper presents results of a systematic laboratory NMR characterization of pure montmorillonite clay with an objective to clearly document the NMR signature of the water adsorbed on the clay surface. This will help establish a physical basis for the application of NMR in shaly sand formation evaluation.
NMR relaxometry experiments on clays and clayey rocks have shown that the adsorbed water on the surface of clays (or the so called clay-bound water in petrophysics) is fully represented in the NMR T
2
distribution. Accordingly, it is desirable to provide NMR characterization of different clays for use in the interpretation of nuclear (i.e., density & thermal neutron) and NMR porosity logs acquired from shaly sand reservoirs.
Cross plots, overlays and modeling of the log responses with respect to the formation lithology are common techniques in the evaluation of density and neutron porosity logs. Bulk density and neutron porosity values for wet and dry clays are required inputs for such evaluation. Compilations of nuclear logging parameters for various sedimentary minerals, including those for wet- and dry clay minerals have been published in the prior art. See, Edmundson and Raymer, (1979), Ellis et. al., (1994), and wireline logging service companies, such as Halliburton, (1991) and Schlumberger, (1994). Bulk density and neutron porosity values for water-wet montmorillonites published in these compilations are based upon chemical analyses of the clay or theoretical derivations of chemical formulae that include certain fixed number of water molecules per unit cell of montmorillonite. In one aspect, the methods of this invention are used to refine the above wet-clay parameters based on new insights obtained from an NMR study of the physical characteristics of the adsorbed water on montmorillonite surface.
NMR characterization of clays, and more specifically montmorillonites, combined with other spectroscopic data (Touret et. al., 1990) can offer petrophysically meaningful values for the quantity of water associated with montmorillonite occurring in the sedimentary rocks. Deeper understanding of the mechanism of water retention by clays, such as montmorillonite, and of the geometry of the space occupied by the clay-bound water provide a physical basis to quantify the adsorbed water in clays irrespectiv
Chitale Dattatraya V.
Coates George R.
Day Peter Ian
Sigal Richard F.
Arana Louis
Halliburton Energy Service,s Inc.
Pennie & Edmonds
Vargas Dixomara
LandOfFree
System and method for clay typing using NMR-based porosity... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for clay typing using NMR-based porosity..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for clay typing using NMR-based porosity... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3141721