Combined characterization and inversion of reservoir parameters from nuclear, NMR and resistivity measurements

#1. Field of the Invention

#The invention is related generally to the field of interpretation of measurements made by well logging instruments for the purpose of determining the fluid content and permeability of earth formations. More specifically, the invention is related to methods for using Nuclear, Resistivity and Nuclear Magnetic Resonance (NMR) measurements and/or measurements made with a formation testing tool or pressure tests made in laminated reservoirs for determining a distribution of sands, shales and fluids in the reservoir and estimating permeability of the reservoir.

#2. Background of the Art

#FIG. 1 (PRIOR ART) shows a resistivity imaging tool suspended in a borehole;

#FIG. 2 (PRIOR ART) is a mechanical schematic view of the imaging tool of FIG. 1;

#FIG. 2A (PRIOR ART) is a detail view of an electrode pad for the tool of FIGS. 1, 2;

#The present invention is best understood by referring to FIGS. 1-7. FIG. 4 is a schematic flowchart of the major steps of the process used in the present invention. FIG. 1 shows a composite imaging tool 10 suspended in a borehole 12, that penetrates earth formations such as 13, from a suitable cable 14 that passes over a sheave 16 mounted on drilling rig 18. By industry standard, the cable 14 includes a stress member and seven conductors for transmitting commands to the tool and for receiving data back from the tool as well as power for the tool. The tool 10 is raised and lowered by draw works 20. Electronic module 22, on the surface 23, transmits the required operating commands downhole and in return, receives digital data back which may be recorded on an archival storage medium of any desired type for concurrent or later processing. A data processor 24, such as a suitable computer, may be provided for performing data analysis in the field in real time or the recorded data may be sent to a processing center or both for post processing of the data.

#FIG. 2A is a schematic external view of the unified borehole sidewall imager system. This may be used to provide the data that may be used in an optional embodiment of the invention. The tool 10 comprising the imager system includes four important components:1) resistivity arrays 26; 2) electronics modules 28 and 38; 3) a mud cell 30; and 4) a circumferential acoustic televiewer 32. All of the components are mounted on a mandrel 34 in a conventional well-known manner. The outer diameter of the assembly is about 5.4 inches and about five feet long. An orientation module 36 including a magnetometer and an inertial guidance system is mounted above the imaging assemblies comprising resistivity array 26 and televiewer 32. The upper portion 38 of the tool 10 contains a telemetry module for sampling, digitizing and transmission of the data samples from the various components uphole to surface electronics 22 in a conventional manner. Preferably the acoustic data are digitized although in an alternate arrangement, the data may be retained in analog form for transmission to the surface where it is later digitized by surface electronics 22.

#Also shown in FIG. 2A are three resistivity arrays 26 (a fourth array is hidden in this view). Referring to FIG. 2B, each array includes 32 electrodes or buttons identified as 39 that are mounted on a pad such as 40 in four rows of eight electrodes each. Because of design considerations, the respective rows preferably are staggered as shown, to improve the spatial resolution. For reasons of clarity, less than eight buttons are shown in FIG. 2A. For a 5.375″ diameter assembly, each pad can be no more than about 4.0 inches wide. The pads are secured to extendable caliper arms such as 42. Hydraulic or spring-loaded caliper-arm actuators (not shown) of any well-known type extend the pads and their electrodes against the borehole sidewall for resistivity measurements. In addition, the extendable caliper arms 42 provide the actual measurement of the borehole diameter as is well known in the art. Using time-division multiplexing, the voltage drop and current flow is measured between a common electrode on the tool and the respective electrodes on each array to furnish a measure of the resistivity of the sidewall (or its inverse, conductivity) as a function of azimuth.