When implementing any Enhanced Oil Recovery (EOR) or tertiary recovery project it is critical to understand the key variables that influence the success of the scheme -reservoir parameters and fluid properties -and the behaviour of the existing development scheme. The additional components of miscible fluid fronts in heterogeneous carbonates, sources of miscible injectant and the systems needed to manage a miscible EOR development will generate additional uncertainty to that already present during primary and secondary recovery.This paper describes the reservoir on which evaluation of CO 2 miscible EOR has been carried out, the reasons it is a candidate for CO2 EOR and identifies the key uncertainties that will have a major impact on the behaviour of a CO2 development scheme; namely fluid distribution, reservoir structure, compositional variation and reservoir property distribution. A key element of the paper is describing how the uncertainties are recognised and managed by the modelling philosophy, given the relatively immature status of the reservoir development and the limited historical data available.The paper describes the interpretation of incremental benefits of CO 2 EOR over existing development schemes. A small component of the paper discusses options of appraising CO 2 EOR further, the approach and need to pilot injection patterns and concepts of phasing development of CO 2 into an existing pattern development. Uncertainty range will reduce over time and the paper describes how work emphasised the importance to recognise when this range is acceptably small to make decisions that involve larger capital investment, such as new development options involving additional wells and facilities.Although the majority of work done in this study was on subsurface elements, this paper briefly touches on infrastructure needed for CO 2 EOR and implications of the scheme on existing facilities. Also considered are the external influences that impact EOR value, such as the source of CO 2 , price of fluid streams entering and leaving the system, and potential for the scheme to be a CO2 storage option once EOR benefit is exhausted.At present in Abu Dhabi, CO 2 or Miscible Injectant (MI) EOR has been recognised as the EOR development of choice by a number of different studies. The fluid types and pressure/temperature regimes in Abu Dhabi reservoirs mean that miscible flooding is likely to be the most appropriate mechanism to further increase recovery factors. Using CO 2 also has the benefit of demonstrating CO 2 capture and likely storage at a time when the UAE is seeking to curb carbon emissions. Improving the understanding of how CO2 can play a role in Abu Dhabi reservoirs is therefore highly topical.

Array induction measurements have been routinely used in the Mahakam Delta, Indonesia, in near vertical wells with oil-based mud and little or no washouts. In these conditions, even a small separation of the shallow focused curves from the deep curves gives a reliable indication of the mud filtrate invasion. The presence or absence of resistive invasion has been used as an indicator of water or hydrocarbon-bearing reservoirs. However, in deviated wells (above 30–40 degrees) the standard focused induction curves may exhibit erratic spikes and curve separation. Therefore, without proper corrections for the dip effects, the separation of the focused curves cannot be used as a reliable indicator of invaded zones and consequently for hydrocarbon typing in deviated wells. To investigate the effects of the relative dip on the array induction measurements in the Mahakam Delta's specific environment of thinly laminated shaly sands and whether these effects can be properly dealt with, a 3D forward modeling project was conducted. Two 80-m intervals were selected from a neighboring vertical well to build a resistivity model. 2-D inversion was applied to recover the bed boundaries and resistivities. The resistivity model was used in the 3-D forward modeling to produce an array induction response in the 45-degree deviated well. To reduce the computational costs, intervals with no invasion were simulated with a 1-D modeling algorithm without a borehole, since the borehole effect could be easily corrected for the oil-based mud. The 3-D synthetic response combined with the 1-D response for both standard vertical well processing and well-site enhanced processing (Inhomogeneous Background Focusing -IBF) allowing for the dip-effect correction. The results clearly indicate that the dipping bed effects for the 45-degree deviated well can significantly distort the focused curves, if data are processed as in a vertical well. These distortions manifest themselves as an artificial separation that does not permit fluid typing. After the dip-effect correction with the IBF processing, the focused curves show no separation in an uninvaded formation (as desired) and depict appropriate separation in invaded layers, which again allows for reliable fluid typing. Introduction Contemporary induction resistivity logging instruments are typically multi-array and multi-frequency induction devices.1 The multitude of acquired data provides an opportunity to resolve the formation conductivity more precisely using advanced focusing and inversion techniques.2,3,4 The standard focusing methods used in real-time processing software assume that the borehole perpendicularly penetrates the formation layers. When the relative dip is large (greater than 30–40 degrees), the focused induction curves may exhibit erratic spikes, misleading curve separation, and inaccurate resistivity values, preventing log analysts from accurately evaluating invasion and formation resistivities. A special processing technique, called Inhomogeneous Background Focusing, has been developed to correct for the dip effects.5 The array induction measurements have been routinely used in the Mahakam Delta a near vertical wells drilled with oil-based mud and boreholes with little or no washouts. In these conditions, even a small separation of the shallow focused curves gives a reliable indication of the mud filtrate invasion. The presence or absence of invasion has been successfully used as an indicator of formation fluid type. Currently, we are considering running the array induction tool in deviated wells with a relative dip around 45 degrees. If the focused resistivity curves are not properly corrected for the dip effects, the separation of the focused curves cannot be used as a reliable indicator of the invaded zone. To investigate the effects of the relative dip on the array induction measurements in the Makaham Delta specific environment and whether these effects may be properly dealt with, the forward modeling project was initiated.