This study evaluated the potential for application of miscible nitrogen injection to South East assets in Abu Dhabi which include three giant onshore oil fields. MMP (Minimum miscibility pressure) for different N2- oil systems was determined as a key criterion for screening. CMG simulation and correlations approaches were employed for determining pure N2 MMP. Results of the study demonstrated that pure nitrogen miscible injection is promising for some reservoirs in the SE fields when reservoir pressure is higher than the MMP. Different correlations have been investigated for suitability to Abu Dhabi crude oils. Investigated MMP correlations are applied to the available data sets and a comprehensive error analysis is performed based on a comparison of the predicted value using published correlations with the simulated value using CMG simulator. Two simulation methods were employed to calculate MMP's: cell to cell and key tie line. The Hudgins and Sebastian correlations are in a good agreement with the simulated MMP indicated by small absolute deviation of 10.9% and 2.9% respectively. Glaso, Hanssen, and Firoozabadi correlations produced unrealistic results. The impact of critical parameters such as C1 fraction, C2-C5 fraction, and molecular weight of C7+, API, and temperature on the MMP of nitrogen injection was investigated.
This paper describes optimal field development and appraisal in complex reservoirs and challenging environments in field ‘ABC’. Most of the wells are laterals with ICD (lower) completions across heterogeneous carbonate reservoirs. Highly corrosive environments i.e. up to 20% H2S present an added risk, particularly in the event of water encroachment. Optimal development needs a multi-disciplinary surveillance approach involving an integration of input form stakeholders, including geoscience and petroleum engineering, to ensure productivity optimization during the whole life of the field. Field ABC is an offshore field with extremely heterogeneous carbonate reservoirs and acid stimulation is usually done to improve production. The wells in the field are mostly horizontal, oil producers with ICD lower completions. The upper completion uses carbon steel L80 and for corrosion mitigation, inhibitors are injected through chemical injection valves. In this paper, a pilot well is reviewed where a methodical approach was used for evaluation. Baseline production logging and reservoir saturation monitoring were done in the lower completion and a corrosion log was acquired in both the upper and lower completions. Data acquired was integrated and observations show that the measurements correlate well with each other. This case study integrates and correlates downhole zonal contribution, phase holdups, pressure and temperature data from production logging with metal loss data from a high-resolution multi-finger caliper tool. Well trajectory shows a depression across the heel of the well which is incidentally between the EOT and the topmost ICD. Although there is no water production at surface, a static water sump is observed across this depression on the production logs. This static water is possibly completion fluid or unremoved fluid from the acid job. Minor localized corrosion is also observed across the same depression on the corrosion logs, also confirming presence of some water. The H2S production and the presence of water is an added risk to completion integrity as it creates a corrosive environment. Therefore, in such cases it will be necessary to monitor the production and corrosion at regular intervals of time. This case study shows that by applying a multi-disciplinary approach and integrating various measurements, well conditions can be viewed not just as pieces of a puzzle but as a complete picture to improve the understanding of the well behavior. Time-lapse monitoring of production and corrosion along with reservoir saturation is also necessary to prevent surprises and help in making informed decisions towards better field development.
Miscible CO2 injection is a method to increase oil production. Combinations of Carbon dioxide with other gases as miscible solvents are emphasized in this paper to improve CO2 miscible injection process. Emphasis is on identifying CO2 solvent mixtures with reduced MMP to achieve miscibility at reasonable injection pressures in Abu Dhabi fields. Two targeted crude oils (Oil 1 and Oil 2) from Abu Dhabi carbonate reservoirs are utilized. The minimum miscibility pressure (MMP) of targeted oils with mixtures of N2, CH4, C2H6, and HC rich gas of varying composition with CO2 injection gas are evaluated through simulation. Cell to Cell and Semi-analytical (key tie lines) methods are applied using CMG simulator. Results show that miscibility is predicted to occur with multiple contact miscibility (MCM): vaporization and/or condensation mechanisms. The increase of C2H6 concentration in the CO2 injected gas reduced MMPs for targeted Oil 1 by 100 psi/10 mol%. However, N2, CH4 and HC rich gas increments in CO2 injected gas increased the MMPs for targeted Oil 1. MMP was observed to be 2300 psi for pure ethane with Oil 1. In addition, MMPs for targeted oils with N2/ C2H6 and N2/ CH4 injected gas mixtures are assessed. This study can open possibilities for future enriching of CO2 and N2 miscible injection to improve miscibility and recovery of oil.
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