A Study On Induction Logging Response In Interactive Thin Layer

The three component array induction logging tool is the newest induction logging instrument. It can effectively measure the conductivity and thickness of the interactive thin layer and give accurate evaluation of oil and gas reservoir. This kind of tool has a broad application in oil field with low porosity, low permeability, and low resistivity. The response characteristics of three-component array induction logging tool in thin layer are studied in detail by the COMSOL finite-element software. The research result has an important theoretical and practical significance for the design of three component array induction tool and the interpretation and evaluation of the logging response.Firstly, the configurations and measuring principles of both array induction logging MIT and three-component array induction logging are introduced. The numerical compution technology of thr three-component array induction logging respnse in the thin interaction layer based on the COMSOL finite-element software is studed. The response the three-component array induction logging in the no-hole three layers and five layers thin interaction layer models is caculated respectively. The problems of the set of boundary conditions of geometric model and grid division for the special thin layer are solved. The other solved problems include the adding source to model, formula derivation of the receiving mode, setting of the solver and so on. Results show that the vertical coil system can not effectively distinguish thin layer. For the horizontal coil, when the spacing between transmitter and receiver is less than thin layer thickness, the layer can be distinguished effectively. When the spacing between transmitter and bucking coil is less than thickness, the layer also can be recognized by the character point of transmitter into or out the layer. Otherwise, due to the complexity of the position relationship among the transmitter, bucking and receiver in layer and the big change in response, the thin layer can not distinguished. In addition, the logging response is seriously influenced by the shoulder formation. Its reading does not equal the thin layer’s conductivity. Through analysises of the thin layer of anisotropy, thin layer thickness change, conductivity contrast change between thin layer and surrounding rock, we show the horizontal coil system for thin layer has good recognition ability, and the spacing of two coils has an important effect on the recognition of.thin-layer.Secondly, the response characteristics of three component array induction logging in the thin layer interaction with borehole are calculated and analyzed. Establish the three thin layermodels with borehole. Analyze the response characteristic of tool in thin layer interactionmodel when parameter is changed, such as tool location, diameter, shouder, and mud. Resultsshow that when the borebore radius is fixed, the mud conductivity increases, the impact onshort array is greater than long array. When borehole radius constant, the position of tool isdifferent, the value of the apparent conductivity is also different. When mud conductivity fixed(10S/m,1S/m, and0.5S/m), borebore radius changes, for large mud conductivity, the biggerthe hole radius, the more obvious change for short array response,, long arrays change smaller;for the small mud conductivity, eight subarray responses change very small as the wellboreradius, so the borehole effect can be ignored.Finally, the distribution characteristics of the electromagnetic field are investigated bydrawing lines of electric current and magnetic field. Calculate the responses of tool in the thininteraction layer with and without borehole. Consider factors including source location,diameter, thickness of thin layers, mud and shoulder conductivity. The analyzing results showthat the interface on thin layer generates eddy current when the emission source is in a thinlayer. The phenomena reflection and transmission will emerge when the eddy current passthrough the thin layers and the shoulder. At same time, the magnetic field lines change withthe change of the current lines. When the position of the source changes in the thin layer, thedistribution of electromagnetic field in the formation is different. The greater the thin layerthickeness, the stronger the magnetic field distribution, the weaker the magnetic field eddycurrent from the up and down surrounding rocks to infinity. When the borehole radius isconstant, the larger the mud conductivity is, the stronger the magnetic field distribution in thethin layer. The mud conductivity decreases the magnetic field distribution in a thin layer.