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.

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Matrix-acid stimulation is a key production enhancement technique for carbonate reservoirs. The ability to control acid placement by diversion along the reservoir section is often challenging, particularly for heterogeneous formations where low-permeability intervals may remain under-stimulated. In this paper, we demonstrate via subsequent inflow profiling that efficient stimulation of both low- and high-permeability segments can be achieved using a completion method called a Smart Liner and a new methodology of downhole flow monitoring without operational well intervention by utilizing inline tracer system across the lower completion. The Smart Liner is a completion technique, which relies on a number of small and unevenly spaced holes to divert acid along a horizontal drain, while incorporating swellable packers to isolate segments with different reservoir properties. The hole spacing design is unique for each well and requires a software algorithm to balance the outflow. The inflow monitoring is assessed through both inline chemical tracers and conventional PLT. Main components of this algorithm has been presented in an earlier publication. The inline tracer system can provide "wireless" continuous production profiling without the risk & cost associated with conventional PLT methods. The inline tracer samples were collected during both stages of pre-stimulation and post-stimulation activities on oil producer wells, which shows downhole contribution of all segments, acid arrival and enhancement of Mid section of the reservoir drain. Moreover, PLT was conducted to validate inline tracer results. Past deployments of Smart Liners have targeted homogeneous reservoir intervals, but in this paper, we show that also reservoirs with significant permeability variation can be effectively matrix-acid stimulated. It is to our knowledge the first time that inflow profiling of a long horizontal well has been probed with inline tracers as well as PLT. Furthermore, we quantify the incremental impact of a given acid volume on injectivity based on the high-frequency data from the stimulation job.

The workflow is implemented for designing Lower completion with inflow control devices &/or inflow control valves (ICD/ICV) for high departure long horizontal wells in a Green Field located North West offshore Abu Dhabi. The major challenges that being faced in the field development include reservoir heterogeneity with high permeability contrast ranging from 0.1 to 500 md, fault network and high uncertainty about Tar Mat surface & Oil Water contact. Main objectives of ICD/ICV completions are; to have uniform influx/flow profile from all sublayers of reservoir by dividing horizontal drain in compartments based on reservoir properties variations, minimize heel to Toe effect, controlled inflow from high permeability streaks, without compromising total well deliverability; most importantly to encourage more inflow from the lower permeability regions. The ICD/ICV Completion design workflow utilized in the industry and available in literature was followed along with new improved & integrated approach of dynamic simulation modelling. An appropriate reservoir sector model having one deviated gas injector, one/two horizontal water injector(s) and one ICD/ICV candidate oil producer was extracted to be used for this study. Single time step static modelling and dynamic sector modeling simulation approaches were implemented for ICD/ICV modeling. The dynamic simulation model workflow included Local Grid Refinement across the candidate well & gas injector along with well segmentation. Sensitivity & optimization cases include Open hole (base) case, ICD/ICV completions with different nozzles sizes, and varying compartment/segment lengths for better control & improving oil flow profiles, and cumulative oil production. This workflow has provided valuable design data prior to drilling this challenging horizontal well candidate, lower completion equipment allocation based on compartment requirements and final optimization of ICD/ICV after receiving open hole logs; where latest suit of logs were run, are discussed in this paper. The completion design of the well resulted from this workflow included ICD configurations with swell packer arrangements to create 8 compartments along the reservoir section. Simulation results from ICD/ICV completion proved successful in delaying water & gas breakthrough in representative multi-well dynamic sector model. This Workflow adopted by the team in designing the lower completion resulted in successful installation of the ICD(s) & ICV(s) in the field for various oil producer wells. This paper also covers the challenges being faced while real time fine tuning of ICD/ICV design model. This workflow would be useful for any future designing & applications of this type of smart completions for any field worldwide with similar challenges.

This paper presents the successful integration of an advanced nuclear magnetic resonance (NMR) log, a source-less technology, with core data and other openhole logs to resolve the challenges of reservoir characterization (including identification of tar mat) and to place the wells in targeted reservoirs zones. This enabled subsequent inflow control devices (ICD) completion design for optimal production in these complex carbonate Jurassic reservoirs. A comprehensive suite of advanced logs, conventional logs and core data were used. The wireline suite covered conventional (resistivity-density-neutron-gamma ray-acoustic) and advanced (NMR-elemental spectroscopy-image) technologies in one of the pilot wells. In another calibration well, data gathering was achieved with wireline (resistivity-density-neutron-gamma ray) and LWD NMR to log the same reservoirs. Integration using these conventional logs, advanced logs and core data established the correlations to derive permeability in this complex carbonate Jurassic reservoirs. From these study wells, a correlation was established between the NMR porosity, density/neutron porosity and core porosity to enhance confidence on NMR-measured porosity. The NMR permeability index was calibrated using parameters that were developed by integrating NMR results with the core data. This permeability relationship (core and NMR) was applied in all lateral wells with LWD NMR results that targeted the same reservoirs in the field. For delineating the tar mat interval, a combination of NMR, density and resistivity measurements was used. The LWD NMR results provided real-time reservoir characterization with rock quality (porosity distribution, permeability) that helped in ICD completion design and enhanced well placement. This approach and technology also enabled substantial rig time savings and reduced HSE risks. This approach demonstrates strong benefits of data integration and proven LWD NMR source-less and lithology-independent technology, in addition to the resistivity and gamma ray, as the preferred solution for advanced reservoir characterization, ICD completion design, and enhanced well placement in complex carbonate reservoirs. The solution for reservoir characterization enabled confident decisions on ICD completion design and enhanced well placement by implementation of source-less technology, eliminating the risks of using radioactive source-based technology.