A geomechanical facies-based approach to optimize drilling and completion strategy of an unconsolidated sandstone reservoir, Saudi Arabia

Drilling horizontal wells, single and multilateral, is nowadays common practice for Saudi Aramco in most of its oil and gas reservoirs (elastics as wells as carbonates) in Saudi Arabian fields. This study highlights the application of a geomechanics study to evaluate well stability drilled into a friable eolian oil-bearing sandstone reservoir. Saudi Aramco's reservoir management was eager to find the optimum mud type and azimuthal direction to place long reach horizontal wells, so as to minimize the risk of stress-induced borehole breakouts, optimize drilling mud weights, aid in making informed decisions about adequate completion design, and ensure sustainable production under depletion mode. The reservoir rocks in this field are characterized as a "wet" eolian depositional system with four distinct depositional facies: dune, sand sheet, paleosol and playa. Grouping the lithology into these four recognizable depositional facies significantly enhanced the understanding of facies dependent rock properties and related wellbore integrity. Hence, a critical objective of the study was to combine the knowledge of reservoir and material properties with detailed analyses of the present day in situ stress field. Upon determination of the in situ stress field in the study area, wellbore stability in the principle horizontal stress directions (S _hmin and S_Hmax) was calculated and compared and the resulting optimum direction was recommended. The effect of mud on rock strength was evaluated and the mud type that caused less rock-strength reduction was selected. The study concluded that under undepleted conditions horizontal wells should be drilled with oil-based mud parallel to the field-derived maximum principal horizontal stress (S_Hmax) azimuth in order to maximize borehole stability and minimize required mud weights during drilling and completion. The results from this detailed study will beincorporated into Saudi Aramco's reservoir management decision tree, in order to maximize wellbore integrity during drilling and completion such that least damage occurs to the reservoir during drilling and in-gauge hole conditions for successful sand control completion deployment can be maintained.