Potential oil recovery derived from exploration wells

In this project we aimed to develop a method for an early identification of the optimal production strategy for an oil-field from the start-up and through its life-time. Early awareness and identification of the potential of improved oil recovery (IOR) schemes may significantly reduce the field infrastructure costs, decrease the amount of chemicals needed and hence enhance the economics of IOR and reduce the environmental impact. Today, the oil saturation and the effect of different IOR methods is determined by using logging tools and/or by extracting core samples from the reservoir for analysis in a laboratory. A core that is removed from the reservoir tends to change nature and properties when depressurized. Consequently, the remaining oil saturation cannot be determined in the laboratory with sufficient accuracy by conventional core analyses. In POREX a new tracer-based methodology enabling in-situ measurement of remaining oil saturation during the drilling and well completion processes was developed. Tracer candidates were found, and an appropriate detection concept was chosen. A 2D experimental set-up was made to verify and improve the understanding of the flow patterns and the physical and chemical processes involved. The set-up consisted of a frame 27x27x1.5 cm3 filled with partially hydrofobic glass beads or alternatively ordinary glass beads, and with 10 ports for inlet/outlet of fluid. Thus the model can accommodate most flow patterns. Water flooding and oil flooding has been done and both water tracer and partitioning tracers have been investigated. The 2-D pattern was visualized with visible tracers and video recorded. The flow patterns are complex and were compared with 1-D signals from the outlet port to construct production curves. The experiments showed that the POREX principle can work. At the end of the project a 2D core-block set-up made of sandstone was made and tested with tracers. For best possible understanding of the flow-dynamics, one-phase simulations with both stream line models and regular grid models have been performed. The simulations reproduces the tracer area distribution, but cannot so far reproduce some of the complexity observed. The simulations points to a rate dependent complex tracer distribution if there are inhomogeneities in the thickness. It could also be that the permeability changes when the pressure increases. The results of these experiments and simulations may be used in the construction of a tool, which will be equipped with tracers, tracer detection equipment and selected IOR chemicals and deployed downhole via a wireline tool. This equipment should enable measurement of remaining oil in small zones near the well bore as well as testing the effect of different IOR methods downhole. The early measurement of the efficiency of IOR methods, such as LowSal, polymer, surfactant or alkaline flooding, is essential in designing and planning optimal production strategies. The new methodology could be an important planning tool which provides more reliable field data in a relatively short amount of time and at considerably lower cost compared to the extraction of cores. This will allow for the implementation of the most efficient IOR method from the first day of production.

Dette prosjektet hadde som mål å utvikle en metode for raskt og tilnærmet kontinuerlig bestemme den mest effektive utvinningsstrategien for et gitt oljefelt fra starten, med borings- og komplementeringsfasen, og gjennom feltets levetid. En slik metode vil drastisk kunne redusere feltinfrastrukturkostnader, minske mengden kjemikalier brukt i felt og gi mer effektiv drift av oljefeltet. Dette vil redusere miljøkonsekvensene og gi betydelige kostnadsreduksjoner. Tidlig måling av effekten av ulike metoder for økt oljeutvinning (IOR) (f.eks. polymer, surfaktant, LowSal) er essensielt for planlegging av optimal produksjonsstrategi. Grunnet stor kompleksitet i strømningsmønstre ble det i prosjektets startfase laget et forenklet mini-reservoar i form av et 2-dimensjonalt transparent oppsett for å kunne studere tracer-mønstrene og sammenholde disse med den 1-dimensjonale tracer-profilen fra utgangsporten. Dette oppsettet har vist seg meget verdifullt for å studere 2-fase flømming og tolkning av tracer-signalene. Oppsettet kan brukes videre i nye prosjekter for å forbedre og videreutvikle simuleringsmodeller som skal beregne effektene av reservoarflømming med vann og IOR-kjemikalier. Resultatene fra prosjektet indikerer klart at POREX-konseptet er mulig å benytte i et skreddersydd DORA-redskap (Downhole Oil Recovery Analyser). Tracere kan dermed bli brukt i testbrønner ved utvikling av løsninger for EOR flømming av reservoaret. Videre utvikling av in-situ automatisk tracer deteksjon og analyse er nødvendig før en felt-test. I tillegg er det nødvendig med utvikling av teknologiske løsninger for å lokalt kunne injisere vann i nærbrønnsområdet ved DORA-installasjonen. Videreutvikling av 2D-oppsettet og de numeriske metodene vil også kunne benyttes av andre fagfelt som studerer 2-fase og komplekse 2-dimensjonale strømningsmønstre.

This project addresses a fundamental challenge in today's petroleum industry: the estimation of recoverable oil. During development of new fields, there is a substantial uncertainty in the amount of recoverable oil. It takes significant resources to determine the initial oil saturation, oil in place and remaining oil saturation after secondary drainage methods. This is typically done by logging tools and/or by extracting core samples from the reservoir for analysis in a laboratory. A core that is removed from the reservoir tends to change nature and properties when depressurized. Core cracking during depressurization may change the core properties and saturation distributions. Consequently, the remaining oil saturation cannot be determined in the laboratory with sufficient accuracy by conventional core analyses due to the inherent uncertainties in the method. In POREX we will develop a new tracer-based methodology enabling in-situ measurement of remaining oil saturation during the drilling and well completion processes, a technology that is currently not available. A tailormade tool (Downhole Oil Recovery Analyser, DORA) will be equipped with new project developed tracers, tracer detection equipment and selected IOR chemicals and deployed downhole via a wireline tool for provision of in-situ data that are further processed with IORSim. DORA will be a modified wireline tool provided and operated by a major service company. The proposed methodology provides early remaining oil saturation field data and allows for new possibilities in production planning involving future IOR strategies. The early measurement of the efficiency of IOR methods, such as LowSal, polymer, surfactant or alkaline flooding, is essential in designing and planning optimal production strategies. The new methodology will be an important planning tool which provides more reliable field data in a relatively short amount of time and at considerably lower cost compared to the extraction of cores.