Mature Basins Characterization and Opportunities Assessment. Case Study on Golfo San Jorge Basin Argentina

Abstract

Abstract This paper examines the maturity degree and potential of the Golfo San Jorge basin which represents 50% of Argentina's daily oil production and 2/3 of its oil reserves. It has approximately 40,000 wells drilled to date and its daily oil, water and gas production are 39, 505 Mm3/d and 15 MMm3/d respectively with 509 Mm3/d of water injection (as of December 2016). The GSJ basin was discovered in 1907, being the first developed oil basin in Argentina. A thorough revision of production and injection history, well status, drilling history and reserves data for 160 fields, combined with lessons learned from more than 15 years of experience, 5000 wells and several detailed waterflooding (WF) studies, allowed to classify different maturity degrees in order to preliminary assess the currently reported reserves and detect opportunities to increase recoveries. The opportunities detected were grouped in two main categories: Optimization of ongoing WF processes: these are low risk / low investments activities aiming to improve contacted area and/or sweep efficiency andDevelopment: infill drilling and pattern configuration optimization with injection re-allocation to add new volumes which were previously inaccessible due to the original flooding design. On one hand, the estimated ultimate recovery by natural drive was obtained by adding the cumulative volumes to date and the production forecasts (Oil 3P reserves) and an OOIP was inferred for each field by assuming a primary recovery factor based on main fluid and reservoir characteristics. On the other hand, a similar analysis was done with the secondary RF, calculated to compared with the average secondary RF obtained from analogous fields. Objectives of this analysis are (i) to assess the maturity degree of a basin by characterizing the development of each field considering primary and enhanced recovery history and including the analysis of its reported reserves and (ii) identify potential opportunities to increase recovery. The basin's OOIP resulted in approximately 6,500 MMm3 with almost 90% coming from fields being under different stages of WF Processes (early or partial WF development to terminal fields with WF). The maturity analysis showed that more than 50% of such OOIP comes from fields in an early and/or advanced WF processes, whereas 40% comes from mature fields with the remaining 10% of the fields being at an early stage of development with almost no WF/EOR. The current reported 3P Oil Reserves and Contingent Resources are approximately 415 MMm3 (394 MMm3 are Reserves and 21 MMm3 Resources at December 2015). Provided the assumptions made are accurate enough, the comparison of the calculated vs analogous fields RF led to the estimation of almost 300 MMm3 of potential opportunities by Optimization (ongoing WF processes) and Development (infill drilling and boosting injection rates). The analysis provided a quantitative indicator to challenge the current view of the maturity of the basin, presenting a novel framework to analyze each field and/or project. These results highlights the importance of making the necessary effort in de-risking and analyzing with enough detail such potential to check for the validity of the assumptions, hence the quantification of the opportunity.