Constrained LWD Resistivity Modeling for Improved Formation Evaluation of Horizontal Water Injectors

摘要

Formation evaluation in horizontal wells (I.e., water injectorsrnas well as oil producers) is generally a challenge becausernfactors affecting formation resistivity measurements arerndifficult to identify, evaluate, and correct for. These factorsrninclude shoulder beds, anisotropy, borehole size, and mudfiltraterninvasion. For oil producers in thick carbonaternreservoirs, because formation resistivity is high, uncertaintiesrnin formation resistivity have only minor effects on waterrnsaturation calculation. For horizontal water injectors (HWI)rndrilled in water swept areas of thick carbonate reservoirsrnbecause the formation resistivity is low, errors in formationrnresistivity directly translate to errors in calculation ofrnformation water saturation. Therefore, accurate formationrnevaluation of HWI requires an accurate estimation ofrnformation resistivity.rnIn this study, one-dimensional (1D) and two-dimensionalrn(2D) resistivity modeling was performed on two HWI, bothrndrilled between a pair of two vertical water injectors. The 1Drnmodeling was used to identify the dominant factors affectingrnresistivity measurement and correct for environmental effects.rnThese results, along with logs from the two vertical wells,rnwere used to construct a local geological model used as inputrnto 2D modeling. To enhance the modeling work, thisrngeological model was further refined by using logging-whiledrillingrn(LWD) density images of the two horizontal wells.rnBoth 1D and 2D modeling results of the two horizontal wellsrnwere constrained with data from the two vertical wells.rnWithout modeling, formation water saturation calculated inrnthe two HWI was too low. With the modeled formationrnresistivity, more accurate water saturation was obtained in thernHWI when compared to the vertical wells. This studyrndemonstrated the power, the usefulness, and also the challengernof resistivity modeling in formation evaluation of HWI inrnwater swept areas.