Evaluation of Chemical Application as Pilot to Improve Oil Production from High Viscous Oil in Sandstone Reservoir

Abstract

Chemical injection stimulation is one of worldwide proven technologies for viscosity reduction and mobility enhancement. The principle mechanism is to reduce heavy oil viscosity by injecting of active chemical agent solution into reservoir as huff and buff practice, the agent solution is act at near wellbore area by remove plugging of heavy organic material, Energy support due to large quantity of stimulation liquid being injected into the formation, viscosity reduction by emulsification and micro-emulsion which will greatly enhance oil mobility; therefore, accelerate oil recovery and reduce interfacial tension (IFT); therefore, increase oil recovery. as global oil industry many technologies introduced to Sudanese oil fields such as chemical which had been implemented in 2018 to increase oil production by developing high viscous oil reservoirs. The pilot was done in two wells in Moga and Fula fields; they are located at southern part of western escarpment trend of Fula sub-basin, Main oil-bearing distributes in Aradeiba, Bentiu and Abu Gabra formations. Bentiu formation was selected for pilot, it is consolidated medium productive sand stone reservoir as per well test interpretation productivity index is 0.05 to 0.2 bbl/day/psia, PVT features: low bubble point pressure, low gas oil ratio (GOR), viscosity at initial pressure between 396–5902 mPa.s and 8986–13880 mPa.s at surface pressure and 29°C, permeability lab test results show strong heterogeneity formation. This paper discusses the chemical injection as enhanced oil recovery (EOR) application in block-6, investigate and evaluate pilot results, then discuss lesson learned from this pilot. Basic reservoir engineering principles and lab test result had been used to calculate production and reservoir parameters before and after implementation. The results of first well shows instantaneous downhole fluid level (DFL) raising about 129 m and remain stable while same pump speed was maintained after the chemical injection, the water cut dropped from 64% to 42% and Oil rate jumped from 95 BOPD to 204 BOPD. second well shows bad performance post the chemical injection and the oil rate decreased from 60 to 40 BOPD and WC increased from 70% to 93% due to well located in the down dip close to OWC and strong reservoir pressure support.