Feasibility Study of Artificial Lift Modes for Deep and Heavy Oil Reservoir

Abstract

Abstract Effective exploitation of deep and heavy oil reservoirs is a strategic objective for KOC. It is observed that suitable mode of artificial lift is required to produce these reservoirs. Objective of present work, is to evaluate diverse challenges, offered by various artificial lift methods, to produce these reservoirs. Scope of work includes selection of appropriate artificial lift technology along-with suitable production methodology, to facilitate sustained production from these reservoirs. This study is carried out for representative deep and heavy reservoir of KOC. Perforation zone is at 9300 feet. Viscosity of well-fluid is 7800 centipoise at reservoir temperature of 190°F. API gravity of well-fluid is 10. It is known that well-fluids can flow to the well-bore; but cannot flow to the surface. Analysis of various artificial lift systems, such as, Gas Lift, SRP, PCP, ESP and Jet Pump, is carried out, with reference to the available well data and field operational constraints. Study also encompasses need for any other technology, which is required along-with artificial lift, to produce this reservoir. It is observed that it is not possible to use either SRP or PCP because both have limitations, to operate, at high depths. It is not possible to employ gas-lift, due to constraints related to availability of injection gas. ESP and Jet Pump, are the only two technically feasible lift modes. It is perceived that ESP is more suited than Jet Pump, with regard to the issues, like, cost, operational ease, surface foot-print and HSE. However, with regard to our simulation studies, it is observed that it is not possible to produce this reservoir, with ESP alone because due to high viscosity of well-fluids. Therefore, use of downhole heater below down-hole ESP or continuous injection of suitable viscosity reducer, below down-hole ESP, is considered. Either of this, add-on utility can help to reduce viscosity of well-fluids, to such an extent; wherein, it is possible for down-hole ESP, to lift well-fluids up to the surface. Study also entails laboratory work, which is carried out to select suitable viscosity reducer, with reference to the oil sample of this reservoir. It is concluded from simulation studies that target rate of 500 b/d can be achieved with ESP, to produce this reservoir, provided it is backed-up by proper mechanism, to reduce viscosity of well-fluids, before well-fluids enter into the pump. Study has adequately addressed challenges, offered by various artificial lift modes, to produce deep and heavy oil reservoirs. It is also inferred from the studies that coherent integration of suitable lift system with other compatible technologies, is essential, to achieve sustained production from this reservoir. The study constitutes crucial benchmark for us, to decide future production strategy to exploit similar reservoirs. The study can serve, as a useful reference guide, for exploitation of deep and heavy oil reservoirs, of comparable nature.