Iwaki-Oki Gas field was a project jointly developed by Teikoku Oil Co., Ltd.（currently INPEX CORPORATION）, Esso Exploration Inc.（currently Exxon Mobil）, and East Japan Oil Development Co., Ltd. Since the successful drilling / discovery of hydrocarbon reservoirs in 1973, a total of 9 exploration / appraisal wells have been drilled, evaluated and abandoned. After these appraisal campaigns, a platform was installed in 1983, and production began in July of the same year while simultaneously drilling and completing total of 15 development wells in 1984. Production from Iwaki-Oki platform ended in July 2007, and the wells were plugged and abandoned, then conductor pipes were cut and recovered in the same year. The platform was unmanned in 2008, and preparatory work for platform removal from the end of 2009. The platform decommissioning work was carried out at July 2010. At that time, these works were recorded in a video for future reference. In the 2020 JAPT symposium, we released this recorded video since the decommissioning of the offshore platform is rare in Japanese oil companies, and we hope that this video will give oil / gas development companies an idea of the work and will serve as a reference for the companies in the future.

Well decommissioning is the last stage of the well life cycle. At this stage, a well is required to be properly plugged and abandoned restoring "caprock" so that any fluid is not discharged from its original formation. JX Nippon Oil & Gas Exploration Corporation（"JX Nippon"）controls the well decommissioning design and operation by the internal management system and technical standards. Whilst the well decommissioning is required to be done satisfying various technical requirements in the standards, the operation should be effectively optimized at the lowest possible cost. This paper introduces three examples: 1）background of the well abandonment due to well integrity issue; 2）well and facility decommissioning operation in GoM; and, 3）optimization of the cement plug in well P&A design, that JX Nippon had recently experienced.

Technological and financial issues associated with decommissioning and well plug and abandonment （P&A）in petroleum development are the focus of growing concern in petroleum development fields owned by Japanese E&P（Exploration & Production）companies.

Therefore, multiple petroleum development fields owned by Japanese E&P companies demanded to survey the trends of technological issues regarding decommissioning and well P&A, then a survey of the latest technological trends （"Trend Survey on Decommissioning and Well Abandonment"）was conducted in 2016.

The survey was contracted to and performed by the Xodus Group in UK.

The survey covered various topics such as decommissioning and well P&A technologies; equipment disposal methods; costs, laws and regulations; health, safety and environment（HSE）; stakeholders; and decommissioning/well P&A follow-up.

JAPEX has variety types of abandoned wells. There are not only wells abandoned because of their well life, but also ones abandoned because they have too high pressure to keep well integrity at surface. In the other case, the well location has been gradually surrounded by residential land after long terms was passed since exploration. In addition, JAPEX has a case that the wellhead of its abandoned well was exposed by construction of third party at the previous well location already returned, and JAPEX recut the casing and set the well cap again. In this presentation, some well abandonment operations that have variety of restrictions, also future well abandonment plan and applications are introduced.