Three‐dimension (3‐D) Numerical Mode‐Matching (NMM) is selected to deal with resistivity logging responses in nonsymmetric conditions. First, an appropriate Descartes's reference frame is set up: the plane of deviated borehole and normal of formation is regarded as plane XOY , and formation strike is regarded as Z axis direction. In the plane XOY the finite‐element method (FEM) is used and a series of two‐dimension (2‐D) generalized eigenvalue problems are solved; whereas vertical analytic is adopted along Z axis. In analytical section, the medium is sliced into some layers artificially, and the relationship between adjacent layers is derived according to the electromagnetic field continuity, namely boundary transition matrices rather than reflection and transmission matrices theory in the 2‐D NMM method. Finally, a system of linear equations is constructed according to the natural boundary conditions that the topmost layer bed has no up‐going wave or the bottommost layer has no down‐going wave, and the potential of every point of formation is solved and the apparent resistivity is computed. In the given formation model, the results of 3‐D NMM agree well with previous ones of 2‐D NMM and FEM in symmetry conditions. Furthermore, the algorithm also applies to with formations titled angle and elliptical borehole; and some examples illustrate how all kinds of formation models with tilt angles affect logging response results.

This paper is a case study in an Ordovician carbonate, east China. Most carbonates are buried hill of Ordovician age and the reservoirs are dolomitized. Fractures are very important here as the porosity is often very low (about 2-5%). But the puzzle is the higher fractured zones not always are the higher production zones. So the two important things that one should be concerned with are (i) how to find the fractured zones, and (ii) the factors influenced the production rates. An integrated approach using a combination of borehole image and NMR logs is applied in this study. Borehole images are used to extract fractures, vugs, rock textures and pore textures. Structure profile across the wellbore is created from the image dips as well, as an aid of the fracture analysis. NMR Bin data and T2 distribution spectrum are displayed to reflect pore textures, and a relative permeability also calculated from NMR logs. Furthermore, the morphic rock types are classified in details base on borehole images and lithology identified with other openhole logs. Nine morphic rock types are identified. All the summary data are displayed in one integrated plot for thorough analysis. The reservoir properties are found well related to morphic rock types and pay zones are observed located near the fault zone. Faults in one hand enhance the reservoir by dissolution on fracture and vugs near the fault zone, while in the other hand, it impair permeability of the fractures with clays in the fault zone. Those clay filled conductive fractures can be seen in borehole image, but no any permeable indictors in NMR data. The vuggy fractured dolomite is deemed as pay zone. The results are validated by the later well production. The combination of borehole image and NMR logs provide a valuable solution for clear understanding of this reservoir.

This paper is a case study in an Ordovician carbonate, east China. Most carbonates are buried hill of Ordovician age and the reservoirs are dolomitized. Fractures are very important here as the porosity is often very low (about 2-5%). But the puzzle is the higher fractured zones not always are the higher production zones. So the two important things that one should be concerned with are (i) how to find the fractured zones, and (ii) the factors influenced the production rates.An integrated approach using a combination of borehole image and NMR logs is applied in this study. Borehole images are used to extract fractures, vugs, rock textures and pore textures. Structure profile across the wellbore is created from the image dips as well, as an aid of the fracture analysis. NMR Bin data and T2 distribution spectrum are displayed to reflect pore textures, and a relative permeability also calculated from NMR logs. Furthermore, the morphic rock types are classified in details base on borehole images and lithology identified with other openhole logs. Nine morphic rock types are identified. All the summary data are displayed in one integrated plot for thorough analysis. The reservoir properties are found well related to morphic rock types and pay zones are observed located near the fault zone. Faults in one hand enhance the reservoir by dissolution on fracture and vugs near the fault zone, while in the other hand, it impair permeability of the fractures with clays in the fault zone. Those clay filled conductive fractures can be seen in borehole image, but no any permeable indictors in NMR data. The vuggy fractured dolomite is deemed as pay zone. The results are validated by the later well production. The combination of borehole image and NMR logs provide a valuable solution for clear understanding of this reservoir.