Research On The Dip Effect Of Array Induction Logging

With the continuous development of petroleum exploration technology,the number of the cluster well,branch well and high angle well increases gradually.The presence of the angle between the shaft and the formation causes abnormal phenomena at the layer boundary of the logging curve,resulting in difficulties in interpretation and evaluation of oil and gas.In order to study the effect of dip angle on array induction logging in high dip formation.Aim at array induction logging instrument HDIL,different stratigraphic models are established based on COMSOL multiphysics finite element software,and the dip effects of different stratigraphic models are studied The research results provide a theoretical basis for the interpretation of array induction logging in high dip formation.The main research results are summarized as follows.The angle response characteristics of the three layer formation without borehole are studied in the first part.The model of three layer formation without borehole is set up.The whole process of modeling and the treatment method of mesh generation are expounded.The applicability of the model is determined by comparing the numerical solution with the analytical solution.The effects of the thickness of the target layer,the conductivity of the surrounding rock and target layer and the inclination angle are calculated and analyzed.The results show that the response characteristics of high dip array induction logging depend on many factors such as thickness,conductivity contrast and dip angle.When the angle is less than 30 degrees,the response results are less affected by the angle.When the angle is greater than 30 degrees,with the increase of the dip angle,the influence of the dip angle increases gradually from the short array to the long array and the main receiver enters formation from the high resistance to the low resistance,the interface appearing the "horns".The angle response characteristics of non intrusive three layer formation with borehole are studied in the second part.Based on the first part of the study,the wellbore model is added to calculate and the angle response characteristics of the mud conductivity,the contrast of the target layer and the shoulder bed,the thickness of the target layer,the borehole diameter and tool eccentricity are calculated and analyzed.Results show that the existence of the borehole weakens the "horns" phenomenon caused by the dip effect,the bigger the caliper,the shorter the array spacing,weakening more obvious.When the instrument is eccentric in the plane of the borehole and the formation,the dip effect makes reference point offset,the offset is equal to the eccentricity divided by cosine of dip.Dip influence and borehole effect are independent approximately,so they can be corrected separately by the method of vertical borehole correction.The analysis of distribution of the space eddy current line at interface and plane eddy current flow distribution reveal the mechanism of borehole weakening "horns" and explain the phenomenon that the logging response curve is broadened or compressed when the tool goes through a high conductivity boundary from the low conductivity.The influence characteristics of dip angle on the formation of three layers with borehole and invasion are studied in the third part.The response features of array induction HDIL in six models with high dip and invasion are investigated.In the low resistivity shoulder models,when the conductivity of invasion is less than that of the formation,the effect of the invasion can be neglected and the dip angle causes the recording position change.When it is greater than that of the formation but less than that of the shoulder,the effects of invasion and dip angle can be separated.When it is greater than that of the shoulder,effects of the invasion and dip angle for the short arrays can be separated,but for the long arrays,it cannot be separated.In the high resistivity shoulder models,when the conductivity of the invasion is less than that of the formation,the invasion affects obviously the short array,and the high angle affects obviously all arrays,and both effects cannot be separated;when it is larger than that of the formation,the features are similar to the low resistivity shoulder case,but the high angle makes the long array appear the obvious "horn" phenomenon.The mechanism of the array induction response is revealed through the analysis of the reflection phenomena and the spatial eddy current distribution at the interface.The analysis of the invasion effect of the actual high angle logging data verifies the validity of the conclusion.The dip response characteristics of the formation with interlayer and the anisotropic formations are studied in the fourth part.For the formation with interlayer,the influence of interlayer thickness,thickness of target bed,interlayer conductivity,target conductivity,shoulder conductivity and angle on the response of array induction logging is studied and the response mechanism is analyzed.For the anisotropic formation,the response characteristics of dip angle under the conditions of horizontal resistivity constant anisotropic coefficient change,vertical conductivity constant anisotropic coefficient change and anisotropic coefficient constant with or without borehole are studied respectively.The results show that the measurement value of long array increases with the increase of the anisotropy coefficient,and the short array is less affected,the vertical conductivity is constant,and the measured value decreases with the increase of the anisotropy coefficient in high dip formation.