Objectives, Scope This paper provides valuable insights on aqueous retarded acid system evaluation based on laboratory testing, literature review and engineering analysis prior to the field application for a candidate well in a gas field, offshore East Malaysia (Figure 1). The field is a reefal carbonates build-up overlayed by a thick shale sequence and is one of the deepest fields in Sarawak Asset, in which the produced fluid contains up to 3,500ppm H2S, 20% CO2 and bottomhole temperature up to 288°F. Production enhancement for this carbonate reservoir requires application of a more effective approach to address challenges associated with acid placement and reservoir contact in long pay zones of complex diagenetic facies high temperature carbonate reservoirs, thereby improving return on investment. Figure 1Structural map of Central Luconia carbonate platform offshore Sarawak, Malaysia (Janjuhah et al. 2016) Methods, Procedures, Process The workflow adopted for the stimulation job involves thorough historical production data analysis, detail petrophysical review to evaluate reservoir properties, in-depth production performance analysis (i.e. nodal and network modeling), completion review to ascertain damage mechanism and economic evaluation that include decision risk analysis to evaluate all range of probabilistic outcome. Initial selection of stimulation fluids was based on the mineralogical composition of the main producing formation. A detailed study of reservoir rock and its reaction to various acid systems has been based upon software modeling where sensitivity analyses involving multiple treatment schedule scenarios incorporating various acid and diverter fluid systems are considered. Coreflood experiment was then performed to determine the Pore Volume to Breakthrough (PVBT) comparing emulsified acid with aqueous retarded acid at temperature of 250°F, injection rate of 3ml/min and at confining pressure of 1,500psi. The low PVBT values (i.e. 1.125 and 0.521) and unique breakthrough features obtained from the coreflood confirmed that aqueous retarded acid is effective to stimulate the carbonate reservoir. Compatibility testing was also conducted to assess the stability of the retarded acid recipes and potential reaction with reservoir fluids (i.e. water and condensate), downhole completion and surface equipment. Results, Observation, Conclusion An established stimulation software was used to refine the acid volume calculation and placement analysis. Field trial was made using combined application of the aqueous retarded acid and viscoelastic diverting acid. Considering several case scenarios, the remedial treatment was performed via bullheading to achieve optimum injection rate within 5bpm to 7bpm. Total of 197bbls acid and 197bbls diverter was be pumped during the treatment that will be split in several stages to achieve average invasion profile of 2.8ft and -1.3 skin value. This paper presents aqueous retarded acid system as alternative to widely used emulsified acid systems. Field application of the approach supports the theoretical findings based on substantial improvement in well production, pressure matching of the remedial treatment and calibrated nodal analysis assessment. This demonstrates the value of holistic approach of laboratory testing, comprehensive software modeling and application of enhanced stimulation fluids to overcome complex technical challenges Novel, Additive Information The field production was previously constrained by its high CO2 levels and the supply gas ratio agreement. The information and lessons learnt from this paper will be applicable as evident of practical improvements to achieve sustainable production from the field since it has a strategic importance as production, processing and export hub to other four gas fields. Recent CO2 blending project has allow a better distribution of gas across the network and therefore demand higher production from the field, thus further unlock it potential to achieve economic optimization.
PETRONAS Carigali Iraq BV (PCIHBV) is the Operator for an onshore oil field which is located in a 30 km x 10 km Contract Area at the southern part of the Republic of Iraq. One of the key activities undertaken by PCIHBV during the development and production campaign is well intervention which involves acid stimulation, well clean up and unloading of newly drilled wells. The conventional practice in Iraq for acid stimulation and well clean-up operation for carbonate reservoir is to burn the recovered hydrocarbon at dedicated flare pit area. This is normally followed by Multi Rate Test (MRT), which takes up to 10 hours of continuous flaring operation for each perforated zone. Some of the critical challenges posed by the above approach include managing and ensuring safe operation for personnel working in this rig-less operation. The flaring activity would release unburned oil, gas fumes, noise, heat and black smoke to the environment. Moreover, there had always been interruptions from the nearby communities who were affected by the release of fumes and smokes from the flaring activi ty which had adversely impacted their health and the surroundings. This situation had regrettably resulted in hostile protests by the affected villagers which could be a threat PCIHBV operations. A technical assessment was conducted to devise a safer, secure and environmentally friendly approach to replace the conventional flaring method. At the same time, PCIHBV also envisioned to minimize the duration required from flaring activities. A new approach called "Zero Flaring" was introduced. The concept of Zero Flaring is meant to treat and neutralize the recovered crude during well clean up and divert the flow towards oil processing facilities. This will then rule out the need to burn the recovered crude in the flare pit. To implement the ‘Zero Flaring" only a minimal site modifications were required with few additional equipment such as chemical injection skid, tanks, sampling points and associated connection. This method has totally eliminated the need for flaring while safeguarding the asset integrity of the processing facilities. This innovative approach has been acknowledged by the Host Authority as it has resolved the flaring issues with minimal expenditures required. As of March 2019, PCIHBV has conducted new wells unloading using "Zero Flaring" method in more than 10 wells. PCIHBV is committed to further improve the ‘Zero Flaring’ method to reap its benefits. This new method has showcased PCIHBV's commitment, values and capabilities as a prudent Operator to safely and timely deliver the production targets without neglecting the social wellbeing of the surrounding communities, the protection of the environment and the integrity of the asset. Above all, it has strengthened PCIHBV's presence in this region and further enhanced our reputation as an International Oil Company (IOC) of choice.
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