Since the two oil crises in the 1970s, E&P companies have been engaged in exploration and development with the belief that discovering and commercializing large reserves is a real charm of exploration and increasing production and reserves has been considered a mission for oil companies. On the other hand, oil price fluctuations and climate change countermeasures in the last three years have been changing more rapidly than ever before, and the movement toward energy transformation（EX）and social demand for decarbonization are becoming irreversible. Under these circumstances, what should oil companies aim for in their E&P business? First, an extreme energy conversion is not realistic, and a sustainable supply of oil and natural gas based on the premise of a thorough low carbonization is necessary for the "transition period" until clean alternative fuels are ready. Natural gas, in particular, will continue to be an important energy source during the transition period as an alternative fuel to coal or as a raw material for blue hydrogen and ammonia. A realistic roadmap for EX is needed, which includes making the project more resilient by promoting near-field exploration, fast track development and reducing E&P costs. It will also include making the business cleaner by performing CCS, electrification of plants and converting coal to natural gas to reduce GHG emission.

Considering the gradual transition from oil & gas to low-carbon or cleaner energy in the future, it is important to develop new technologies that have affinity with the core technologies of oil companies, such as monitoring CO₂ injection layer by using higher resolution 3D/4D seismic data. Furthermore, it is becoming increasingly important to have a sense of speed in exploration and development in order to avoid the projects from becoming stranded assets.

東南アジア地域の新生代堆積盆地の多くは高い炭化水素ポテンシャルを有しており，各堆積盆地における石油システムの解明・特徴づけが行われている。その結果，東南アジア地域にはリフト期（漸新世）およびポストリフト期（中新世）に，それぞれ別の根源岩が存在することが示唆されている。前者はリフト発達時に堆積した湖成頁岩であり，埋没深度が比較的浅いより小規模な堆積盆地（例えばベトナムのクーロン盆地）に掘られた坑井において，油生成能力の高い湖成根源岩が確認されている。埋没深度がより深く実際に同じ層準まで坑井が掘り込まれていない大規模な盆地（パタニトラフ，マレー盆地，南コンソン盆地など）においても，盆地発達史の類似性から，同根源岩の発達の可能性が想定される。後者はリフトが埋め立てられる過程で堆積した河川～デルタ成の根源岩（石炭層）である。東南アジア地域の新生代の石炭層は水素に富み，ガスだけでなく油も生成する能力があることが知られている。

東南アジア地域には，このようにタイプの異なる根源岩において，その分布域や熟成域，油ガスの生成タイミングが異なる複数の石油システムが存在する。そのため探鉱段階では有効根源岩を特定し，複雑な石油システムを理解する必要がある。有効根源岩を推定する手法の1つとして，原油やコンデンセートのバイオマーカーや同位体組成を利用した地化学インバージョンがあり，広く用いられている。これにより坑井で直接掘り込めない盆地中心部の深部に存在する有効岩の特定も可能となる。さらに各根源岩の熟成度や油ガスの生成タイミングは堆積盆地シミュレーション，いわゆるベースンモデリングにより評価することができる。

本スタディでは，近年発見されたベトナム沖のガス田から採取された流体試料（油・コンデンセート・ガス）において地化学インバージョンを実施した。バイオマーカーおよびダイヤモンドイド化合物の解析により，2つの油ファミリー（湖成と河川～デルタ成の混合原油および河川～デルタ成原油）が見出された。また炭素同位体組成から，湖成根源岩由来のガスと河川～デルタ成根源岩由来のガスが貯留層中で混合した可能性が示唆された。さらに，対象ガス田の岩石試料に対して流体包有物分析を実施したところ，一部の貯留層においてパレオ油コラムの存在を示唆する多数の油包有物が確認された。この貯留層は現在ガス・コンデンセートを胚胎していることから，もともと集積した油は後からチャージしたガスによってフラッシュされた可能性がある。また多次元ベースンモデリングにより，2つの根源岩から生成されたタイプの異なる流体が移動・集積の過程で混合したこと，さらに対象ガス田に更新世以降多量のガスがチャージすることにより，もともと集積していた油ガスが周辺構造へスピルアウトした可能性が示された。

The results of pioneering carbon dioxide capture and storage（CCS）projects such as Sleipner and Gorgon are widely recognized as milestones in the early days of CCS. The reservoir formations of the pioneering projects are characterized by homogeneous sandstones that develop over several hundred meters thick. On the other hand, sandstone formations expected to work as reservoirs for CCS in Japan are characterized to be more heterogeneous and thinner than those of pioneering projects as above because of the tuffaceous sandstones typical of volcanic arcs. In addition, the geological formations in Japan that separated by complex faults in active continental margins might not be suitable for CCS reservoirs. However, we will have to make CCS feasible against these "challenging" formations. In this paper, examples of multidisciplinary approaches for geological evaluation of domestic depleted oil fields obtained from a joint study with INPEX are shared, and we hope that those findings would help future CCS projects in Japan.

In carbon dioxide capture and storage（CCS）projects, monitoring the plume and potential risks, for example, induced seismicity, is essential for safe and stable operation. Although the effectiveness of the monitoring technologies has been proven by existing pilot-scale projects, optimizing cost-benefit is necessary for large-scale CCS projects. However, there are many candidate methods and it is sometimes difficult to select an appropriate combination from them. Also, when grand design of the CCS project is not well recognized and the risk analysis is not implemented at the beginning, it often results in unnecessary confusion in planning the monitoring scheme. To tackle the challenges, visualizing the whole framework needed for monitoring design is proposed. We examined several published projects and extracted monitoring frameworks common to most of them. Also, the technology ranking method was reviewed for quantitative comparison of different monitoring methods. Based on these, we started our monitoring plan by teaming up with a variety of technical experts and listing up candidate monitoring technologies. We found that this approach was effective since we could build and share the concept of CCS monitoring through repeated discussions from the start. This made inter-technical cooperation possible, and the unbiased selection of monitoring technologies was achieved. We also started the process by assessing risk scenarios since we could understand from the extracted frameworks that a riskbased monitoring plan is essential for CCS projects. Understanding the whole framework enabled us to mitigate undesired confusion between each expert. We also discuss some of the newly recognized challenges in our monitoring design.

One of the key issues in gas production from methane hydrate-bearing reservoir is the excessive water production from adjacent aquifers and other sources. As a countermeasure, it is necessary to reduce the permeability of the surrounding aquifers to a distant extent. As a process of making this countermeasure possible, we are exploring the possibility of applying waterglass-based water blocking agent generally used in the construction industry. This paper presents the results of the experiment and numerical simulations and the direction of future studies.

In addition to an analytical result of two gas samples, published geological and geochemical data on the Isobe gas field, which had produced CO₂ commercially during about 30 years, are examined in this paper from the viewpoint of petroleum geology

Chemical and carbon isotopic compositions of gases from the field indicate that CO₂ is magmatic origin and has no relationship with hydrocarbons which are derived from the thermal decomposition of organic matters. Faults are ascending paths of CO₂, which is driving force for hot spring waters.

Chemical and isotopic compositions of associated waters with gases which are used as hot spring waters indicate that the waters are fossil sea waters which were entrapped during deposition and undergone diagenetic alteration. Higher temperatures of the waters estimated by the Mg-Li geothermometer than a bottom temperature at 1,500 m depth suggest that the waters are formed in deeper parts and derived from there.