Assessment of Fishbone Well Design Performance in a Tight CarbonateCompared to Single Extra-Long MRC Lateral

摘要

A reservoir simulation study of different fishbone well designs performance compared to a basedevelopment well design of extra-long maximum reservoir contact (MRC) single lateral wells is presented.The objective is to compare different well design concepts in a waterflood recovery scheme to achieveproduction target rate and maximize resource value for economic development of an undeveloped tightcarbonate reservoir.The studied reservoir is located in a giant offshore oil field in the Middle East and wasused as a representation of the different tight reservoirs within the field.It is characterized by poor qualityrocks with a permeability trending from 2-0.5 md in a SE-NW direction.The study compromises an assessment of the achievable initial maximum oil rate,volumetric reservoirsweep and expected ultimate oil recovery factor for different well design concepts for a base short wellspacing utilized for effective pressure support.In addition to that,the impact of fishbone well design onwell count reduction potential utilizing twice the base short well spacing compared to single lateral wellsdevelopment design utilizing the base short well spacing was evaluated.A sector model with equal producer to injector ratio was used with refined gridding to wells and bulkarea gridded with a cell size of 10 m by 10 m in a representative area of the reservoir.The modeled wellsincorporated with vertical flow performance tables with gas lift capabilities.The analysis also incorporatedgenerating streamlines for analyzing fishbone well designs areal reservoir sweep and an examination ofremaining movable oil areal distribution.An assessment matrix was formulated for comparing extra-longMRC single laterals base development design versus different fishbone well designs.The assessment matrixincorporated in addition to reservoir related flow performance indicators: drilling complexity and well cost,well life cycle activities,etc.for a comprehensive assessment.The main findings show that fishbone well designs have complicated areal sweep performance,especiallywith sealed motherbore,that result in a lower oil recovery factor with higher hydrocarbon pore volumeinjected and water oil ratio compared to extra-long MRC single laterals.Also,fishbone well designs haveserious limitations during well life cycle activities compared to extra-long MRC single lateral design interms of stimulation,well accessibility and well intervention options making the extra-long MRC singlelaterals the preferred field development concept within tight reservoirs especially with the base short wellspacing.Finally,the analysis has shown that Fishbone well designs can't reduce the well count since base short well spacing is still needed for effective pressure support by water injection in addition to maximizingthe oil recovery factor within the field life time and building and sustaining the target plateau.