The expansion in recent years in the oil and natural gas sector has a profound implication for the continuous supply of energy in the market. There is no doubt a surge in the domestic natural gas production with tremendous opportunities as gas is used extensively for electricity generation. With the increasing energy demand, it is always a challenge to bridge the supply and demand gap. The era of sweet shallow gas is fast depleting and hence developing local sour gas production having higher concentration of hydrogen sulphide (H2S) and carbon dioxide (CO2), which are toxic and corrosive is seen as the viable solution. Currently, ADCO took up a project to study developing the sour gas reservoirs. The objective of the appraisal program was to gain valuable reservoir data including PVT samples to finalize the facilities and full field development plan including testing the reservoir in an area where seismic data indicated better quality sweet spots. The appraisal program was carried out and the major challenges to drill, test and produce the highly sour HPHT (High Pressure, High Temperature) gas were identified and mitigated. The data from the previously drilled wells penetrating the sour Arab zone was used to drill in the sweet spots identified but additional data was required to reduce the remaining key uncertainties to firm up the Gas In place volumes as the final results were crucial for strategical decisions. This paper highlights the work progress and then the lessons learned during each step of the operation with the proposed mitigation to safely and efficiently drill the appraisal wells in the Arab sour reservoir having 37% H2S and 10 % CO2.
ADNOC onshore recently tested HPHT sour gas reservoirs with +30% H2S, +10% CO2 to evaluate the reservoirs and well potential as part of the efforts in supplying additional gas for meeting country's growing energy needs. Developing these massive HPHT sour gas reservoirs is essential for providing a sustainable source of energy for years to come.
An Offshore Gas Field discovered in early 70' is a large anticlinal structure located in the shallow marine waters west of Abu Dhabi island. The area is considered by UNESCO as Biosphere reserve and is protected. Several development options have been studied to develop the gas reserves from existing Artificial Island with a minimum impact to the environment.Geological and reservoir simulation compositional models have been prepared to optimize the development plan, identify the minimum number of wells, target rates in order to maximize the gas recovery and sustain the gas plateau rate as long as possible. Building these models was a challenge due to the lack of 3D seismic data and the limited production data from the appraisal well. Due to the sensitivity of the area, the main challenges of the project implementation are the impact on the environment during drilling phase and the facilities construction and its operation.The required refurbishment of the existing island and access channel to the island was a concern that was studied. Drilling of 10 to 12 closely clustered directional deviated gas wells from one existing artificial island in the centre of the field into a High Pressure and High Temperature, high H2S (14-24%) and deep reservoirs environment is also a big challenge. To effectively drain the entire reservoir from the island, the rigs should be capable to drill more than 25,000 ft extended reach deviated wells.Reducing the impact on this sensitive environment was the major concern; hence an HSEA study has been carried out to develop the mitigation plans. The possibility of drilling using more than one rig simultaneously on the island to deliver gas on time has been studied to minimize the duration of the drilling operation and associated risks. Special completion materials for these extreme environments were also studied. Material selection for different well types/conditions has been carried out.
Well testing operation of sour wells by flaring or flowing through existing pipe line network with limitations always consider as highly challenging in brown field. In this paper operational and social challenges considered during critical well testing operation during different phases. For initial performance evaluation, completion and surface facilities were not designed as per expected well fluids specially in consideration of H2S, CO2 and elementary Sulphur. These wells located in congested developed field and special consideration regarding social risk analysis and mitigation were considered. Extensive H2S and SO2 dispersion modeling conducted to develop EPZ & EAZ for safe operation by utilizing latest safety equipment's. Special scale treatment and down hole chemical injection adopted to cater tubing accessibility due to elementary Sulphur and other scale issues to improve flow assurance during well testing operation. Case study of condensate storge tank utilization with improved safety precaution will highlight the consideration of reservoir fluids for any well testing operation. High volatile Condensate handling at well site always be serious challenge and can be utilized with extensive HAZOP and better process safety controls. Well intervention operation with High H2S for gas wells in presence of water aggravate corrosion and H2S cracking significantly for any type of metallic material. Special down hole plugs, wire line, E-line and sealing elements of pressure control equipment's designed and utilized during intervention operation along with utilizing of special chemical. Well control is serious concern while flowing such wells due to catastrophic asset and environment impact. Special well control consideration needs to be in place for any well control scenario, this paper will cover all type of surface and subsurface consideration to improve the well & reservoir integrity.
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