Holistic Open Hole Stand Alone Screen (OHSAS) Design Approach in Long Horizontal Oil Wells with Multiple Sub-Units in Depleted Reservoir at Offshore Malaysia
Authors: Madzidah Asba , Hussain Mifdhal , M Ariffin M Syafiq , Ghonim Elsayed Ouda , Sapian Nik Fazril Ain , Tusimin Fuziana , A/L Naupa Nagarajan 
Published: September 2022

Abstract
Open Hole Stand-Alone-Screen (OHSAS) design have been used in the oil & gas industries to monetize unconsolidated reservoirs. Design steps includes optimum screen selection, drill in fluid & breaker design, running in hole procedures, bean up plan & post tie in monitoring. This paper will discuss in detail on overall strategy implemented during OHSAS deployment in Field A, involving 4 horizontal oil wells in AABB reservoir & its post-production results.
OHSAS is selected based on sonic travel time info showing &gt;90usec/ft, Unconfined Compressive Strength (UCS) value ranging from 3000-5000psi & historical sand production. History from offset wells completed with pre-perforated liners, suggested 8 out of 9 wells had history of sand production once producing with high water cut. Screen selections was design based on Particle Size Distribution (PSD) data performed through Laser Particle Size Analysis (LPSA) & Sieve Analysis using samples from conventional & side wall cores. Several samples were then selected to execute the sand retention test (SRT) on different screen sizes & types. Screen placements across the horizontal open hole was designed into segmented zones with swell packer & Autonomous Inflow Control Device (AICD) were used to balance flow contributions along the horizontal sections and GOR control. Modelling work was performed to decide on well segmentation, sensitivity on rates, pressure drop across completion and erosional risks assessments. Selection of drill in fluid & breaker fluid system were designed to ensure the horizontal segment can be drilled effectively with optimum bridging, less susceptible to formation damage & screen plugging. Lab tests conducted to facilitate selections for all wells were production screen test, Permeability Plugging Test & Return Permeability Testing using core samples. OHSAS deployments were strategized to avoid stuck risks associated through dog leg severity management, torque & drag analysis with deployment of optimum centralizer placements to reduce dragged & placement of optimum number of swell packers. Optimization on lower completion were performed based on actual logging resu lts to improve overall well performance through isolation of shaly or gassy segment using blanks, use of tandem swell packer in gas segment & use of optimum AICD valve numbers.
Post completion, specific bean up program was followed to ensure natural sand packing is properly established in the annular space between screen face and the open hole segment within allowable drawdown. Real time monitoring on flowing parameters especially bottomhole pressure through PDG & sand rate (if any) were performed during well tests. Multi rate test & Pressure build up (PBU) test verified that all 4 wells were able to meet at least 20% higher production rates than plan, with no major sand productions produced at surface.
The holistic approach outlined in this paper is important in achieving long lasting application of OHSAS in unconsolidated reservoir right from design to production phase.