Nodal Analysis Optimization of Rod Pumped Wells in Mature Oil Fields: A Field Case Study on Improving Lifting Efficiency and Reducing Downtime

Abstract

Many mature oil fields utilize rod pump artificial lifting methods and struggle with rod pumping technology. These issues cause declining volumes of product produced and increased costs because of decreased volume efficiency associated with frequent downtime due gas interference, fluid knock, and/or rod fatigue failure. This paper presents nodal analysis as a tool to identify and eliminate inefficiencies through systematic optimization diagnostics. A case study for nodal analysis was conducted in a mature oil field by establishing an anonymous site where 15 rod pumps were found and collected a 6-month history of daily production rates, dynamometer card analysis and failure logs. Data collected during this period was used to develop a baseline and follow up after implementing results from the nodal analysis through a pilot program of five selected rod-powered pumps. Data from the nodal analysis consisted of pump ingestion node associated with reservoir inflow performance (using the Vogel Equation), tubing performance (using the Hagedorn Correlation) and pump displacement characteristics. The variables optimized in the design of the pumps were pump depth, plunger diameter, stroke length, strokes per minute, rod string configuration and counterbalance system. The new designs resulted in an increase from 53.7 % to 67.4 % for average volumetric efficiency (a relative improvement of 25.5%, corresponding to an absolute increase of 13.7 percentage points). Downtime was reduced from 85 hours to 17 hours per well per month (from 12 % of operating time to 4.5 % of operating time) and energy consumption per barrel decreased by 13 %. Reduction of 85 % of gas lock events and 60 % of rod separation failures were achieved. Using the nodal analysis-based optimization process improved the lifting capability of mature rod pumped wells and decreased one-time operational downtime through continued improved rod pumped well systems. The entire optimization effort required only routine field data (not specially targeted prospective data) to be collected and processed and can be performed easily and replicated in any similar type mature rod produced well system in the world