A mature offshore field in Malaysia consists of wells that are over 20 years old and completed with dual-strings and multiple packers to produce from different sand layers. Due to the unconsolidated formation, most of the wells were completed with a gravel pack. After many years of production, the water cut has increased and fines migration has gradually plugged the gravel packs and screens. This has resulted in closing in these wells, leaving stranded potential oil behind. Continuing to produce through the plugged screens would require higher drawdown, which in turn induces greater sanding from the nearby reservoir rock and higher water cut. However, working over these wells was often noneconomical. Initially, several wells were treated with acid but were reported to produce sand after the treatment. This was attributed to screen damage and gravel-pack failure requiring costly repair. Additionally, the acid used to remove the plugging caused by the fines migration weakened the matrix, increasing the sanding tendency. This paper presents a case history of propellent stimulation treatment performed in two wells at this field. The gravel-packed wells were rejuvenated by applying a propellent treatment instead of acid treatments to clean the plugging in the gravel packs and screens over selected intervals that are known to be oil-bearing. Zones that could be producing water because of movement of the oil/water-contact can be left untreated so that the plugging in the screens helps in delaying water production. Propellant has been used in the oil industry for many years, but its application has been mainly for minifracturing of consolidated rock in standard cased and perforated wells. Its application to clean gravel pack is not well known and knowledge in this domain is limited. As such, the case study started with candidate selection and proceeded through the proposed solution, conceptual job design, execution, and finally the results of the application.

Dynamic Well Operating Envelop (WOE) allows to ensure that well is maintained and operated within design limits and operated in the safe, stable and profitable way. WOE covers the Well Integrity, Reservoir constraints and Facility limitations and visualizes them on well performance chart (Hamzat et al., 2013). Design and operating limits (such as upper and lower completion/facilities design pressures, sand failure, erosion limitations, reservoir management related limitations etc) are identified and translated into two-dimensional WOE (pressure vs. flowrate) to ensure maximum range of operating conditions that represents safe and reliable operation are covered. VLP/IPR performance curves were incorporated based on latest Validated Well Model. Optimum well operating window represents the maximum range of operating conditions within the Reservoir constraints assessed. By introducing actual Well Performance data the optimisation opportunities such as production/injection enhancement identified. During generating the Well Operating Envelops tremendous work being done to rectify challenges such as: most static data (i.e. design and reservoir limitations) are not digitized, unreliable real-time/dynamic data flow (i.e. FTHP, Oil/Gas rates etc), disintegrated and unreliable well Models and no solid workflows for Flow assurance. As a pre-requisite the workflows being developed to make data tidy i.e.ready and right, and Well Model inputs being integrated to build updated Well Models. Successful WOE prototype is generated for natural and artificially lifted Oil and Gas wells. Optimisation opportunities being identified (i.e. flowline pressure reduction, reservoir stimulation and bean-up) Proactive maintenance is made possible through dynamic WOE as a real time exceptional based surveillance (EBS) tool which is allowing Asset engineers to conduct the well performance monitoring, and maintain it within safe, stable and profitable window. Additionally, it allows to track all Production Enhancement jobs and seamless forecasting for new opportunities.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn general, mature oilfields have a good portion of the remaining reserves still trapped due to inefficient drainage, production decline, increase in water cut and sand production and aging of the existing systems. This paper addresses techniques and initiatives to optimize development plans in a mature field. For Bokor Field in particular, there have been identified and implemented opportunities such as Infill drilling and workover optimization, dynamic underbalance perforation (DUP), matrix acidizing and propellant stimulation, water shut-off mechanical (WSOM), sand management, through tubing stand alone screens, deployment of electrical submersible pumps (ESP) and gas lift NOVA valves, real time surveillance (DHG, DTS and LiftWatchers*) and optimization, and microbial EOR.Before the implementation of these techniques, this field had a daily oil production equivalent to 10 MSTBD (after fields decline) and the current production is 26 MSTBD. The two main reason for this increase are:• New technologies were employed in this oil field with dramatic results incorporating new hydrocarbon reserves, via 3D seismic techniques, high resolution stratigraphy and better static and dynamic simulation models. • Multidisciplinary integrated studies to increase field ultimate recovery factors by improvements in drilling, workover, stimulations, facilities and EOR methods.

An oil sample, collected from the wellhead of a shallow sandstone reservoir, was identified as a very stable crude oil emulsion. This micro-emulsion type crude could not be separated in field separation facilities by gravity settling alone. The emulsion was so stable that it required either a high speed centrifuge or high doses of emulsion breaker to be demulsified. Hence, from the perspective of field operational cost, it is critical to further investigate the potential factors that have contributed to the stability of the crude oil emulsions.The field of interest has been producing for over 30 years and its reservoir pressure has dropped below the original bubble point pressure. All the wells in the field are gas lifted to enhance well productivity. Due to the unconsolidated nature of the reservoir rock, fines migration is one of contributing factors to formation damage. The reservoir crude was identified as biodegraded with missing of intermediate components from the reservoir fluid composition. As such, a structured bottom-hole sampling program was developed and bottom-hole samples were collected below gas lift mandrels while the gas lift was shut-in to thoroughly investigate the contributing factors to the formation of the crude emulsions and to identify the in-situ status of the crude.Potential factors which could contribute to the formation of stable crude oil emulsions include 1) mixing of two or more incompatible crudes; 2) emulsifying agents including surface active materials (asphaltenes and resins, organic acids and bases, injected surfactants or oilfield chemicals) and finely divided solids (clay particles, sands, asphaltenes, wax, scale etc.). This study has investigated several potential contributing factors related to formation of the stable crude emulsions. It was concluded that naturally occurring fines could be the major contributing factor for the formation of the observed stable crude emulsion from the reservoir under study. Effect of gas lift on formation of the crude emulsion was found very minimal since the crude was at emulsion state even at reservoir depth.

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