Abstract
Smart Auto Gas Lift (AGL) refers to a downhole system that utilizes gas from a gas zone or a gas cap in a well to lift oil below or above the gas zone in the same well. This paper illustrates a novel AGL intelligent completion design approach including candidate screening, pre-drill feasibility study, sensitivity analysis, and followed by the completion installation and production operation practices for the first two (2) successfully completed AGL wells in Malaysia.
In the candidate screening process, a novel design approach was used based on a 3D numeric single wellbore dynamic model forecasting method. Firstly, candidate screening was performed for the application suitability of AGL in the candidate reservoir. The key screening factor includes the identification of the source of AGL gas, either from the associated overlaying gas cap or independently from another layer of non-associated gas, estimation of gas pressure and oil pressure, estimation of volume of available AGL gas and longevity of gas reserve throughout oil production life, and considering the reservoir structure and drive mechanism. Secondly, single well prediction modelling analysis was performed to evaluate candidates' dynamic performance on production rate, water cut, gas oil ratio (GOR) profile and pressure depletion over time. This is to make sure designed AGL completion will meet expected various production dynamic responses during the entire life of well. The next step is to conduct production snapshot nodal analysis for the appropriate choke size design for AGL downhole flow control valve. Those dynamic results from the single wellbore prediction model becomes important input for nodal evaluation to simulate changing reservoir conditions at different stages. Finally, various sensitivity analyses on layer properties and valve setting depth are followed to ensure that the AGL valve choke sizing design range is flexible enough to cover expected reservoir uncertainties and to be effective over the entire well life.
Based on above design and analysis approaches, a specified range of AGL valve choke opening were designed for T field candidate wells and smart AGL completion system was installed successfully and safely in two wells by end of 2014 without any health, safety and environmental (HSE) issue and AGL related non-productive time (NPT). The production and well test data were available for production performance surveillance, and the dual permanent downhole gauge system (measuring pressure and temperature in both the tubing and the annulus) at gas zone enabled the continuous auto gas injection monitoring at real time basis. This paper discusses AGL well design approaches, justifications, best practices and lessons learned regarding completion installation, well clean up and production operations to give a general guideline for AGL implementation in this area in the future.
