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Write Librarian, Pipeline Simulation Interest Group, 945 McKinney, Suite #106, Houston, TX 77002, USA – info@psig.org. ABSTRACT Upstream gas supply planning and allocation contains 3 cycles namely long term (20 years - end of life of a field) mid-term (up to 1 year) and short term (72 hours). Since the upstream assets are owned/operated by different companies under various production sharing contracts, each of the operating companies prefer to maximize their production and recover the investment costs at the earliest. A regulator acts as a custodian to ensure that all stakeholder’s entitlements are protected. The custodian relies on economic and hydraulic modelling to analyse the production plateau’s shared by various operating companies together with the demand profiles for viability. The commercial planning team of the custodian works closely with flow assurance engineers before confirming the production numbers as the planners are unaware of any capacity constraints in the physical network for flow. In the short term, an integrated network operator breaks the long term demand numbers and controls the network for seamless delivery of gas from upstream to LNG plants (mostly). The purpose of the paper is to highlight the challenges faced by planners and engineers during the planning cycles and to make appropriate recommendations. INTRODUCTION AND BACKGROUND There are 3 gas regions under the custodian and we focus on one region where the complexity is more as there are several production sharing contracts, a greater number of hubs and junctions and a wide range of gas quality. The network overview of the region under consideration can be viewed in Figure 1. Generally, gas produced by each field is gathered in gas hub and then sent to the risers i.e. FRA, FRB and FRC. These risers are connected to onshore gas receiving facility at a terminal from where they are sent to the LNG plants. In terms of quality, the gases gathered in Riser FRA are normally the sweetest, which corresponds with the stringent requirement in the downstream of the slug catcher SLCat-1. In terms of supply, the highest priority is usually given to the state’s electricity company. The gas gathered in Riser FRA mostly flows to the onshore facility into SLCAT-1, combined with the gas gathered in By and D_351. A portion of the gas flow in Riser FRA also spills over to Riser FRB, combined with the gas produced from the other fields and then flows mainly to the onshore gas receiving facility into SLCat-2 and a portion of it also flows into Riser FRC. Riser FRC is also linked to receive gas directly from M_1 which is a hub gathering gas from SERI and JAN fields. M_1 has the flexibility to flow its gas either to Riser FRB or Riser FRC or both at the same time. Gas in Riser FRB flows into SLCat-2 at onshore via Trunk line 3 and Trunk line 4. SLCat-2 also receives gas from Kum cluster via a different pipeline. At onshore, SLCat-2 has another source of gas which is from SLCAT-1, but this line is normally not used. Principally the flow of the line between SLCAT-1 and SLCAT2 should be controlled to flow only from SLCAT-1 to SLCAT-2 to ensure low CO2 content at Met-1 because CO2 content in SLCAT-2 is commonly higher compared to SLCAT-1. Gas in Riser FRC flows into SLCAT-3 via Trunk line 5 and Trunk line 6. In its current operation, Riser FRC does not receive gas from any other fields except M_1. This situation may change in future with several new fields linked to this riser. At the downstream of SLCAT-2 and SLCAT-3, there are several more different sources of gas. Downstream of SLCAT- 2 has a link from a dry gas diverter manifold which is gas received from another gas terminal via a cross country pipeline apart from FROB. The supply to LNG-2 systems from this PSIG 1913 HYDRAULIC MODELING FOR UPSTREAM GAS PRODUCTION PLANNING AND ALLOCATION – SIGNIFICANCE, CHALLENGES, AND RECOMMENDATIONS Prasad Challa 1* , S.J.K. Sahith 2 , K.V. Rao 3 , Srinivasa Rao Pedapati 4 1* Corresponding Author: Sapura Exploration and Production Inc., Malaysia. 2, 4 Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Malaysia. 3 Department of Petroleum Engineering & Petro Chemical Engineering, JNTUK, India.