Microbial source tracking （MST） is an environmental monitoring technology to trace waterborne microorganisms to the point or non-point sources. In most MST methods, DNA extracted from environmental waters are used as indicators （tracer and/or marker） of the origins of microorganisms in the samples. The usefulness of microorganisms as indicators for environmental monitoring is significantly enhanced by the recent development of DNA sequencing and data-analysis technologies. To date, MST has been implemented mainly in water management, food industry and public health sector for determining sources of fecal contamination. Yet, it also provides petroleum industry useful tools for tracking subsurface fluid flow. In this article, we introduce several examples of MST applications in oil and gas reservoirs. Particularly, through a proof-of-concept trial at a natural gas field in Japan, we propose a simple procedure for data analysis applicable to various fields. DNA were extracted from produced and injected waters from the gas ?eld.
Microbial populations in each fluids were analyzed by 16S rRNA gene amplicon sequencing. Comparison of microbial compositions based on cosine similarity and k-means++ clustering revealed possible communication between wells, demonstrating that MST can provide additional insights useful to improve the operational performance.
Gas hydrates are clathrate compounds in which guest molecule such as methane is in a cage formed by water molecules. Huge amount of carbon is considered to be stored in natural gas hydrates. Thus, gas hydrates attract much attentions as a major reservoir of carbon cycle and a possible future energy resource. It is important to understand reservoir properties of gas-hydrate-bearing sediments for prediction of gas hydrate dissociation behaviors.
However, analysis of sediment samples containing gas hydrates is quite difficult because gas hydrates dissociate during coring, handling, and measuring processes. In this paper, we review a pressure-core analysis technology that is a unique technology keeping sample pressure within the equilibrium conditions of gas hydrates during handling and measuring processes. We categorize the pressure-core analysis technology into three generations according to the technological progress and summarize scientific findings. Finally, we discuss perspective of this technology within and beyond gas hydrate research.
Geochemical characteristics and alteration process during diagensis of formation waters from the Yabase oil field, Akita Prefecture, are discussed using published data.
The formation waters are divided into three groups （type I: shallow reservoirs, type II: deep reservoirs in the northern area, type III: deep reservoirs in the southern area） based on chemical and isotopic compositions. Chemical and isotopic changes of these groups are transitional and reflect the alteration of the seawater trapped in sediments during diagenesis. The type III formation waters, which are characterized by HCO3－/Cl－ ratio >1 and high δ18O values, are strongly affected by the maturation of organic matters and the phase transformation of silica minerals in source rocks around reservoirs.
Li＋ contents of formation waters from the deep reservoirs are less than the seawater and these Li＋/Cl－ ratios are about the same as the seawater. Also, temperatures of the deep reservoirs calculated using the Mg-Li thermometer are slightly lower than reservoir temperatures. These matters suggest that the formation waters are not affected by fluids migrated from deeper parts. Geochemistry of the formation waters suggests that the oil migration is not related to the formation water in this field.
The writer presents an outline of the second geological survey of oil fields in Japan, and Mr. Chitani, who played an active role in the Geological Survey of Japan, and his contribution to petroleum exploration in Japan are briefly described. His classmate at the Imperial University of Tokyo, Dr. Takahashi, is a pioneer in the field of origin of petroleum and petroleum geology in Japan and a part of his achievements is presented in this paper.
The Applied Technology Workshop （ATW） “SPE/JAPT-ATW 2019 Tokyo”, co-hosted by the Society of Petroleum Engineers （SPE） and the Japanese Association for Petroleum Technology （JAPT）, was held for two days at The Westin Tokyo on June 27 and 28, 2019. In this ATW titled “Innovations in Natural Gas - Development, Storage, Transportation, and Utilisation”, the natural gas, which is expected to play a central role in the primary energy mix from the viewpoints of energy security, relatively low carbon dioxide emissions during combustion and ease of use and transport, was focused on, and 10 sessions were prepared for discussing various technologies from upstream to downstream.
Following the keynote speeches in Session 1, Session 2 covered the development of natural gas from both conventional and non-conventional reservoirs. In Session 3, methane hydrate, an unconventional natural gas resource expected in Japan, was raised. Gas utilization technologies such as gas injection, carbon dioxide capture and storage （CCS）, and CCS-EOR （Enhanced Oil Recovery） were discussed in Session 6. Sessions 7 and 8 discussed natural gas processing in the midstream and downstream industries including LNG （Liquefied Natural Gas）, floating LNG, and micro LNG.
On the other hand, digital technologies and technologies for implementing projects in harmony with the environment are expected to be applied at all the stages of natural gas development/processing, and were discussed in Sessions 4 and 9, respectively. In addition to these discussion sessions, six poster presentations were held in Session 5.
A total of 89 persons from 38 organizations in 8 countries, including two chairs, 20 program committee members and 4 planning committee members, participated in this ATW. Opinions and expertise on current status and future prospects of natural gas were exchanged actively, and the meaningful and rewarding time could be shared by all the participants.
This ATW was successfully summarized and closed in Session 10.