Field Implementation of Nutrient Huff and Puff in Bentayan Field, South Sumatera: Towards a Low-Cost EOR

Previous laboratory studies have shown that the combination of molasses and commercially-available fertilizer (NPK and ((NH4)2HPO4) can stimulate bacterial growth that decreases oil viscosity and interfacial tension (IFT). In this project, a huff-and-puff field implementation of MEOR nutrient injection has been conducted in two selected wells in Bentayan Field, South Sumatera, BN-38, and BN-81. The project objective is to evaluate and analyze the effect of nutrient injection towards oil recovery, changes of indigenous microbes that alter oil characteristics from the two selected wells during three months of post-nutrient injection monitoring phase. Changes of oil production were measured in-line after the gross produced liquid passes through a separator unit. The abundance of aerobic, anaerobic, and sulfate-reducing bacteria (SRB) was examined by using Total Plate Count (TPC) method, while anaerobic bacteria and SRB were cultivated using the Hungate technique. The chemical compositions of the oil were analyzed before and after nutrient injection by using gas chromatography-mass spectrometry (GC-MS) method. Fluid analysis of the oil (kinematic viscosity and interfacial tension) were measured by viscometer and IFT meter. The program of nutrient injection started with 500 bbls of first nutrient injection, followed by 100 bbls of post-flush 1, 500 bbls of second nutrient injection, 100 bbls of post flush 2, soaking for 14 days, 2000 bbls post-flush 3, and soaking for seven days. Based on the results of bacterial abundance analysis for three months, there was an increase of almost 1000-fold of total aerobic bacteria abundance and 10-fold of anaerobic bacteria abundance after nutrient injection. The expansion of bacterial abundance successfully changed the physical-chemical condition of the oil, decreasing oil viscosity by approximately 24% and IFT by 47%. In both wells, water cut values were decreased from 99% to 92%, and incremental oil was gained by 1395 barrels. Huff and puff nutrient injection seems to be low-cost EOR since it can be included in the daily operating cost with the additional cost of workforce, nutrient, monitoring, and analysis. Economic analysis calculation of this project resulted in Pay-out-Time (POT) by four months with an incremental gain of approximately 1750 barrels.