Development and Application of New Downhole Technology To Detect Water Encroachment Toward Intelligent Wells

Abstract

Abstract Electrokinetic potentials are generated when fluids flow through rock.We have investigated whether changes measured in electrokinetic potential using permanently installed downhole electrodes could be used to detect water encroachment towards intelligent oil wells.Downhole electrodes in cemented arrays have been successfully utilized in resistivity measurements, but have not previously been used to measure electrokinetic potential.One reason is that it has not been possible to relate changes in potential with changes in saturation.We have reviewed the existing literature and conducted laboratory experiments to determine how the electrokinetic potential varies with water saturation, brine salinity and other key reservoir parameters. We have used the results to simulate numerically the electrokinetic potential response measured at a well during oil production.Preliminary results suggest that encroaching water causes changes in the measured electrokinetic potential which could be resolved above background electrical noise; indeed, water could be detected several 10's to 100's of meters from the well.We have also investigated the optimum response of an intelligent well equipped with downhole inflow control valves.In a simple, conceptual reservoir model, production is significantly enhanced if encroaching water is detected before it arrives and flow into the wellbore is properly controlled. Our findings raise the novel prospect of an oil field in which the wells can detect the approach of water and respond appropriately.Such wells offer enormous potential economic and environmental benefits, particularly in fields which are difficult to access or dangerous to operate. Introduction Permanently installed downhole sensors are increasingly being deployed to provide ‘real-time’ reservoir data during production.Many companies now routinely measure pressure and temperature along hole;[1–9] recently, the deployment of downhole flow meters has also been reported, based on measurements of acoustic velocity or density.[10–12]This data helps to reduce uncertainty in the reservoir description and contributes to reservoir management decisions.[1–7,9,12–14]Where wells are equipped with inflow control valves, it is possible to develop a feedback loop between measurement and control to optimize production.[13]Wells equipped with downhole sensors and control valves are often described as ‘intelligent’ or ‘smart’,[15] and it is widely recognized that they have the potential to significantly enhance production.[2, 13, 15–2]0 In this paper, we suggest that measurements of electrokinetic (or ‘streaming’) potential during production, using permanently installed downhole electrodes, could be used to detect water encroachment towards an intelligent well.Electrokinetic potentials are generated when fluids flow through rock, and although they are increasingly being used in other areas of earth science to monitor subsurface flows,[21–25] there has been little investigation of their utility in hydrocarbon reservoirs.Yet downhole electrodes in cemented arrays have been successfully applied in subsurface resistivity surveys during oil production,[26–28] and similar technology could be used to measure electrokinetic potential. We have used numerical techniques in conjunction with laboratory experiments, to simulate the electrokinetic potential measured at a well during oil production with associated water injection or aquifer influx.Our preliminary results suggest that encroaching water causes changes in the electrokinetic potential at the production well which could be resolved above background electrical noise; indeed, water approaching the well could be detected several 10's to 100's of metres away.This contrasts with most other downhole monitoring techniques, which sample only the region immediately adjacent to the wellbore.Moreover, if the well is equipped with downhole inflow control valves, we demonstrate with some simple reservoir models that production can be significantly enhanced if encroaching water is detected before it arrives, and flow into the wellbore properly controlled.