Resolving True Formation Resistivity and Reconstructing StructuralReservoir Complexity using Resistivity Inversion in High Angle HorizontalWells to Gain Insights into Future Reservoir Production Behaviour andDevise Proactive Completion Strategy-A Case Study from Lower BurganFormation,Minagish Field,West Kuwait

摘要

High angle or horizontal (HA/Hz) wells are commonly drilled to increase reservoir exposure and enhancethe overall production.Whereas reservoir navigation highly advance the correct placement of suchwells,completion decisions for profit or recovery oriented production optimization require thoroughinterpretation of available shallow-and deep-reading formation evaluation measurements.Particularly,complex geological environments necessitate the use of reservoir maps and heterogeneity evaluations tounderstand the likely production behavior.In such applications,formation evaluation measurements from logging-while-drilling (LWD) technologyare affected by the relative geometry between well trajectory and the formation.With increasing depthof investigation of the measurements and geological complexity of the reservoirs,these effects becomemore severe and true properties become uncertain.The multi-propagation-resistivity (MPR) responsesshow so called polarization horn effects at bed boundaries when beds with a high resistivity contrast areencountered.During the process of inverting these resistivities to obtain true formation resistivity (Rt),inversion algorithms help to reconstruct the complex architecture of downhole formation geometries.Thisprovides a better understanding of the geometrical reservoir complexity and provides insight into thepotential future production behavior.Possible corrective actions in production and completion strategies canbe derived from such insight.Additional complications like proximity to water transition zone and waterconing can be predicted and certain corrective measures,for instance blanking particular zones or placinginflow control devices (ICDs) can be taken,potentially increasing the overall life of the well.This case study presents a horizontal well in a layered Lower Burgan sandstone reservoir of West KuwaitMinagish Field,where a new approach of drilling horizontal sidetracks from abandoned and plugged oldvertical wellbores attempted with the purpose of increasing reservoir productivity and tapping into unsweptoil.A sidetrack was placed at the roof of the Lower Burgan and navigation while drilling within this complex reservoir was used to stay close to the lithological boundary.Represented by paleo river channel stackedsand bodies,the Lower Burgan formations are overlain by fluvio-tidal sequences of sandstone-siltstone-minor shale alternations of the Upper Burgan with an undulating nature of the lithological boundary.Steeringand placing the well in close proximity to this undulating boundary was achieved.The production of thiswell is exceptionally high with minimum water cut despite a massively increased water transition zone overthe last decade.The case demonstrates that an integrated interpretation of the reservoir architecture andheterogeneity along the lateral uncovers the reasoning behind the experienced production.Overall,polarization horns were observed on the propagation resistivity curves.While the interpretationof log artefacts from sole MPR and azimuthal propagation resistivity (APR) data is challenging,the creationof a detailed structural Earth model from borehole images and the results from a 1D inversion algorithm wereused to understand geometric effects on the logs qualitatively.The top of the reservoir was modeled as anuneven surface with open bed boundary positions,to represent the undulating nature of the erosional surfacebetween the Lower Burgan and Upper Burgan formations.The used method is an iterative 1D resistivityinversion algorithm and is able to derive more accurate Rt along the lateral and allows to reconstruct andvisualize the downhole geological complexity of the Lower Burgan reservoir.Reservoir heterogeneity wasinvestigated by the distribution of flow and storage capacities along the lateral well using effective porosityand he permeability index from magnetic resonance data.The combined interpretation of the reservoir map,Rt and the reservoir heterogeneity highlighted