A New Nodal-Analysis Technique to Improves Well Completion and Economic Performance of a Matured Oil Field

Abstract

Abstract Mature fields lack the sparkle of a new play, and an operator typically will not invest capital for waterflooding, much less EOR. But prevailing higher oil prices can turn such a mature oil field more profitable by employing innovative production enhancement techniques. We propose the use of a simple, tapered tubing string completion (using larger internal diameter (ID) tubing pipes in the upper sections) that can be customized for specific reservoirs. Historically there are few instances of tapered ID tubing completion, which were basically necessitated by technical constraints (liner, workover, etc.). But our approach is focused on enhancing economic performance. We have employed nodal analysis technique to develop an equivalent tubing diameter (ETD) concept. The ETD allows for comparing the well performance for single-ID tubing completion. The procedure also seeks an optimum length for the larger tubing ID in the upper section. Using reservoir simulation for full life cycle, and oil prices projected over time until abandonment, the economic performance is evaluated using NPV and other economic parameters. The proposed production enhancement method is suitable for wells with moderate to high open flow potentials (AOFP). It is especially suited for low GOR wells with high future water-cut that will eventually require an ESP system, and also remote oilfields, where reservoir pressure maintenance and EOR is not viable. The use of larger tubing ID section entails only a marginal increase in CAPEX. However, the tapered completion gives increased production rate sustained over a long time, which results in significant economic gain. The economic benefits accrue from the prevailing high oil price, yielding a quick payout and many returns on investment. The proposed completion approach does not involve complexity, and the innovative application of nodal analysis coupled with high oil prices show how to make mature oil fields onshore and offshore, more profitable. Introduction Nodal analysis was performed in the sixties and seventies by hand calculations, using vertical pressure traverse graphs generated in-house by big oil companies. Smaller operators, if they at all used nodal analysis, relied on Brown's (1963) famous pressure traverse graphs. The workflow was tedious at best, discouraging engineers to explore for horizons that nodal analysis could lead to. However, with the advent of affordable PC software (e.g., Fekete's FAST™, IHS's PERFORM™, etc.), and even MS-Excel™ based spreadsheet programs (e.g., Guo et al. 2007), the power of nodal analysis now can be unleashed even in a classroom setting. One such unexplored horizon is tapered tubing string design - with gradually larger internal diameter (ID) in the upper sections of tubing string. Conventional tubing string design entails selecting a constant internal diameter for all the tubing sections—from bottom to top. The upper sections of the string, however, have a greater wall thickness to support the load of the string below. Thus conventional tubing strings are tapered in terms of outer diameter, which is necessitated by mechanical loading requirements.