One of the major concerns in a multi-layer system is that interlayer cross-flow may occur if reservoir fluids are produced from commingled layers that have unequal initial pressures. Reservoir would commonly have bigger average reservoir pressure (pore fluid pressure) as it goes deeper. The phenomenon is, however, not followed by the reservoir productivity or injectivity. The existence of reservoir with quite low average-pressure and high injectivity would tend experiencing the cross-flow problem. It is a phenomenon of fluid from bottom layer flowing into upper layer. It would strict upper-layer fluid to flow into wellbore. It is as if there is an injection treatment from bottom layer. The study deploys productivity index an approach parameter taking into account of cross-flow problem instead of injectivity index since it is a production well. The analytical study is to model the reservoir multilayer by addressing to avoid cross-flow problem. The analytical model employed hypothetical and real field data to test it. The scope of this study are: (a) Develop mathematical-based solution to determine the production rate from each layer; (b) Assess different scenarios to optimize production rate, those are: pump setting depth and performance of in-situ choke (ISC) installation. The ISC is acting as an inflow control device (ICD) alike that help to reduce cross-flow occurrence. This study employed macro program to write the code and develop the interface. Fast iterative procedure happens on solving the analytical model. Comparison results recognized that the mathematical-based solution shows a good agreement with the commercial software derived results.

Finding new oil and gas that can be developed economically is getting more difficult and challenging today. To meet the oil and gas demand, it is therefore important to focus on the existing and already developed assets by applying new and more efficient technology and optimizing the use of existing equipment to increase production performance of the asset thus better recovery. Sangasanga Field as mature oil field of Pertamina EP is producing its oil by the assistance of artificial lift. The artificial lifts applied in Sangasanga field are Sucker Rod Pump (SRP), Electrical Submersible Pump (ESP) and Hydraulic Pumping Unit (HPU) where SRP dominates with 84 units installed while ESP and HPU are 25 units and 15 units respectively. According to the data of well service work history from 2018 to 2020, the failure of SRP and HPU was quite high. The main problem observed were the occurrence of leaking tubing and broken sucker rods. The study gathered the occurrence of failure and a method so called "WEAR PREDICT 99" was created to estimate SRP's buckling point and lifetime. WEAR PREDICT 99 is a correlation derived from comparing neutral point calculated from formula with actual leak data of broken pipe or suction rod. The correlation then used for predicting the buckling point that represents the probable location of the leaking pipe or damaged suction rod. This correlation allows to predict when and where the sucker rod will leak or break, therefore preventive measures to increase the lifetime of the SRP and HPU wells can be taken.

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