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.

In a green field located in offshore Abu Dhabi, a new well was drilled in an oil-bearing zone and was completed with slotted liner inside a 6-in horizontal drain hole. Abnormally high gas rates were reported during the surface production testing of this well. This paper highlights the unique use of a new pulsed neutron tool combined with an advanced production logging tool for assessment of the well performance and identification of the source of gas breakthrough. This combination of advanced technology tools with measurements from array flowmeters, optical gas holdup sensors, and a new generation pulsed-neutron tool was deployed in the well to provide reliable flow type, borehole, and formation measurements in a gas environment. A multidisciplinary approach involving production engineering, petrophysics, and well integrity was essential in diagnosing this unexpected issue of high gas production. An integration of the various results from production logging, the pulsed neutron measurements, and open-hole and cement log data has helped in confirming the source of the produced gas. The acquired production log (PL) data revealed gas entry from the top of the lower completion and no presence of free gas below that depth. The zonal contributions from the horizontal lateral quantified from the acquired data also helped in assessing the productivity of the reservoir. The pulsed neutron log (PNL) measurements were acquired in the second run, which then helped confirm the borehole fluid properties and to identify and quantify the formation fluids. Combining the PNL and PL data helped identify the gas entry point accurately. Based on the integrated data interpretation, it was confirmed that the gas could not originate from the reservoir being produced through the lower completion and that there must be gas channeling downward through channels in the cement behind the casing from a gas reservoir above the oil reservoir. The unique use of the advanced PNL data and its integration with other log data facilitated the successful identification of the gas source and quantified zonal contributions in a challenging logging environment.

Many wells in the Bu Hasa field in Abu Dhabi are completed with near-horizontal or horizontal laterals in the consolidated Lower Cretaceous carbonate formations. These slim barefoot completions allow improved production and drainage from the good permeability formations in the field, however surface production measurements do not tell the full story on the contributing zones downhole. To improve the reservoir management many production logs with specialized logging technology developed for horizontal wells with multiphase flow, are undertaken in the field. This paper presents a case study of one of these wells that was showing less than expected oil production along with a significant but abnormal water cut. Production logging was done to acquire an inflow profile along the lateral, and a pulsed neutron log for formation fluid saturation was also acquired to diagnose any increased water saturation zones. The production profile showed that less than 40% of the open hole lateral length was contributing and that most of the water was coming from a specific section of the well. The formation fluid saturation profile confirmed good oil saturation across the whole lateral as was expected but there was a clearly higher water saturation across the water-producing section of the open hole. Corrective action was taken on the well after these logs with a completion change incorporating various Inflow Control Devices (ICDs) for the lateral section, and gas lift mandrels for improved lifting capability if required in the future. The lateral was then acid stimulated and put back on production. A second production log, again in combination with the pulsed neutron saturation log, was acquired to review the changes in the downhole inflow profile after the completion change. This profile showed that all sections of the lateral were now contributing effectively to the total oil production confirming the effectiveness of the new completion. Water was still coming from the higher water saturation zone that was again observed on the pulsed neutron saturation analysis, however it was apparent that the AICD was controlling the water entry as per design. Surface production measurements indicate reduced water cut and improved oil production confirming good success with the overall intervention. Currently water cut on the well is still slowly but continuously decreasing while the oil production is also improving. Continued monitoring will provide additional feedback for future water conformance operations in the field to assist in improving recovery factor from the reservoir.