Arthur H. Johnson

Economic geology of natural gas hydrate

Why Gas Hydrate?.- Physical Chemical Characteristics of Natural Gas Hydrate.- Oceanic Gas Hydrate Character, Distribution, and Potential for Concentration.- Natural Gas Hydrate: A Diagenetic Economic Mineral Resource.- State of Development of Gas Hydrate as an Economic Resource.- Oceanic Gas Hydrate Localization, Exploration, and Extraction.- Gas Production from Unconfined Class 2 Oceanic Hydrate Accumulations.- Regulatory and Permitting Environment for Gas Hydrate.- Conclusions and Summary.

Hydrate petroleum system approach to natural gas hydrate exploration

Natural gas hydrate (NGH) is a solid crystalline material composed of water and natural gas (primarily methane) that is stable under conditions of moderately high pressure and moderately low temperature found in permafrost and continental margin sediments. A NGH petroleum system is different in a number of important ways from conventional petroleum systems related to large concentrations of gas and petroleum. The critical elements of the NGH petroleum system are: (1) a gas hydrate stability zone (GHSZ) in which pressure and temperature lie within the field of hydrate stability, creating a thermodynamic trap of suitable thickness for NGH concentrations to form; (2) recent and modern gas flux into the GHSZ along migration pathways; and (3) suitable sediment host sands within the GHSZ. These elements have to be active now and in the recent geological past. Exploration in continental margin sediments includes basin analysis to identify source and host sediment likelihood and disposition, potential reservoir localization using existing seismic analysis tools for locating turbidite sands and estimating NGH saturation, and deposit characterization using drilling and logging. Drilling has validated first-order seismic analysis techniques for identifying and quantifying NGH using rock physics mechanical models.

Hydrocarbon System Analysis for Methane Hydrate Exploration on Mars

The recent detection of plumes of methane venting into the Martian atmosphere indicates the probable presence of a substantial subsurface hydrocarbon reservoir. Whatever the immediate source of this methane, its production (whether by biogenic or abiogenic process) almost certainly occurred in association with the presence of liquid water in the deep (5+ km [3+ mi]) subsurface, where geothermal heating is thought to be sufficient to raise crustal temperatures above the freezing point of water. Indeed, a geologic evidence that the planet once possessed vast reservoirs of subpermafrost groundwater that may persist to the present day exists. If so, then methane generation has likely spanned a similar period of time, extending over a considerable part of the geologic history of Mars. As on Earth, the venting of natural gas on Mars indicates that substantial amounts of gas are likely present, either dissolved in groundwater or as pockets of pore-filling free gas beneath the depth where the pressure-temperature conditions permit the formation of gas hydrate. Hydrate formation requires the presence of either liquid water or ice. The amount of water on Mars is unknown; however, the present best geologic estimates suggest that the equivalent of a global layer of water 0.5–1 km (0.3–0.6 mi) deep may be stored as ground ice and groundwater beneath the surface. The detection of methane establishes the subsurface of Mars as a hydrocarbon province, at least in the vicinity of the plumes. Hydrocarbon system analysis indicates that methane gas and hydrate deposits may occur in the subsurface to depths ranging from approximately 10 m (30 ft) to 20 km (10 mi). The shallow methane deposits may constitute a critical potential resource that could make Mars an enabling stepping stone for the sustainable exploration of the solar system. They provide the basis for constructing facilities and machines from local Martian resources and for making higher energy-density. chemical rocket fuels for both return journeys to Earth and for more distant exploration.

The path to commercial hydrate gas production

During the course of the past two decades, enormous reserve potential has often been attributed to gas hydrates in marine sediments, yet the commercial development of gas hydrates is widely viewed as a possibility which is 20, 30, or more years away. As a result, the oil and gas industry has been slow to pursue this opportunity, and gas hydrate exploration and production research has been a low priority for most energy companies. This perspective is changing as a result of recent research by universities, government agencies, and international consortia. In particular, a better understanding of gas hydrate formation has developed along with geologic models for the concentration of gas hydrate in potential reservoirs. At the same time, emerging production technology should enable gas hydrate production in the near term, limited more by constraints on infrastructure than by production technology. Given projected higher natural gas prices, gas hydrates will likely emerge as a viable commercial resource in so...

Deepwater Natural Gas Hydrate Innovation Opportunities

Natural gas hydrate (NGH) is unique among conventional and unconventional gas resources. It is a stable, solid crystalline material in its reservoir. All deposits worldwide will be found in partially consolidated marine sediments within about 1 km or less from the seafloor, making them highly accessible from the seafloor. Deposits will also occur in the same partially consolidated sand beds. Most of these will be turbidite sands similar in almost every way to those that are older and more deeply buried, and that host conventional oil and gas deposits. NGH deposits are generally not associated with oil or hazardous chemicals. When NGH is inexpensively converted to its constituent gas and water, the resulting natural gas and water offer unique drilling opportunities. NGH deposits have very low environmental risk, even in regions such as the environmentally fragile Arctic. The unique characteristics of NGH concentrations will potentially allow much less expensive exploration, reservoir preparation, and production opportunities. In particular, there are opportunities in drilling and reservoir wellbore plans and new technologies for NGH exploitation that could provide an innovative pulse to offshore energy operations.

Natural Gas Hydrate: Environmentally Responsive Sequestration of Natural Gas

Pleistocene glacial sediments will predominantly host NGH, and possibly only those to depths of no more than 1 km. Older sediments will likely be buried too deeply to host NGH. Each glacial episode would have produced a suite of sediments related to the onset and glacial maximum period and especially during the onset of the following interglacial period when the melting of the ice cap would produce large volumes of water that would strongly affect sediment winnowing and transport. These periods of maximum water flow would be likely to produce the clastic sandy sediments that would be ideal hosts of high-grade NGH deposits in the deeper continental shelves and the continental slopes. In addition, sea level variation would have strongly controlled the position of the shoreline positions during the glacial and interglacial cycles. Sediments within about 1.2 km depth below the seafloor comprise the exploration zone for NGH and related gas deposits. The continental margins of the Arctic Ocean have been divided into 5 regions for analysis of the degree to which they could provide optimal NGH host sediments to suitable depositional environments.

Energy Overview: Energy Options and Prospects for Natural Gas

Availability of energy is key to wealth, political and military power, and living standards. Energy availability and consumption may be the most reliable measure of an economy. There is a direct relationship between energy consumption and countries’ gross domestic product (GDP) and the Human Development Index (HDI). Energy security, which is the relative certainty that energy supplies for a country will be available, constitutes a primary security concern for countries with high energy demands and countries with increasing energy use. Even though there appears to be no immediate shortage of hydrocarbons, this non-renewable resource is being supplemented by renewable energy. The Renewable Energy Era has already begun. Reduction in CO2 emissions is underway because of government regulations and market forces. A completely renewable energy future may be in our future, but its timing is very uncertain as renewable energy presently contributes less than 10% of energy, and that supply is highly concentrated geographically. The potentially largest natural gas resource remaining on Earth, oceanic natural gas hydrate (NGH), may substantially supplement the natural gas supply far into the future. An additional benefit is that natural gas produces less CO2 per Btu and also has a much lower pollution potential than any other combustion fuel. Natural gas is the clean hydrocarbon fuel that will reach into the renewable energy future. Its continued availability at affordable prices becomes increasingly important as coal and oil power plants are retired and energy demand becomes increasingly filled by development of renewable or intermittent power sources.

Valuation of NGH Deposits

Valuation of a natural gas hydrate (NGH) deposit is concerned with determining the amount of natural gas that can be technically extracted from a deposit. NGH will rarely occupy all porosity, probably topping out at 80 % or slightly greater of available pore fill. NGH may also be patchy because of both variable porosity and permeability in the reservoir, and from inconsistent mineralization. There are different ways to value a NGH deposit, (1) reservoir analysis, which is an analog of valuing a conventional gas deposit, (2) 3D body analysis based on high resolution seismic data, and (3) cell analysis, which is an analog of conventional economic geology exploration. In addition to an estimate of gas-in-place, estimates for technical recovery must be made. It is likely that a number of the NGH deposits that will be discovered will occur in discontinuous volumes that are not completely hydraulically linked initially through their pore water because of discontinuous impermeable shale beds and lenses. It should be noted that NGH in place may not be technically recoverable gas in place. Where production wellbores cannot link some NGH volumes, the gas has to be discounted from the valuation figure.

Exploration for Deepwater Natural Gas Hydrate

The potentially large volume of oceanic natural gas hydrate (NGH) resources, combined with new understanding of the NGH petroleum system and demonstrated exploration techniques, suggests that near-term extraction of natural gas from the resource is feasible. Sandy marine turbidite sediments in the Nankai (Japan) and Walker Ridge (US—Northern Gulf of Mexico) localities have been proven to host high concentrations of NGH. NGH is a stratigraphic play insofar as the present primary exploration targets are marine turbidite sands. Sediments of this type, deposited on deep continental shelves and slopes, are a primary target for NGH extraction potential. Similar, more deeply-buried turbidites are prominent first-order hosts for conventional gas and oil deposits. Concentrations of NGH cluster along the base of the GHSZ although NGH is more stable toward its top. These are proven hydrocarbon resources and amenable to extraction of gas and oil. We infer that conversion of NGH to its constituent gas and water will allow the natural gas to be recovered. Exploration tools are sufficient to identify and value NGH concentrations.

New Technology for NGH Development and Production

The main area in which new technology and approaches has the potential to dramatically reduce the cost of natural gas hydrate (NGH) development is in drilling and reservoir planning, and preparation for production. Substantial existing technology and emerging methods being developed for ultra-deepwater, particularly those based on operating processing equipment on the seafloor rather than in vessels overhead, can be used in a re-specified form. New approaches to drilling and reservoir planning are made possible by matching technology to the unique characteristics of NGH in its reservoir, including the shallow depth below the seafloor of potential pay zones, the additional benefits of depressurization-dissociation conversion (Max and Johnson in Advances in clean hydrocarbon fuel processing: science and technology. Woodhead Publishing, Cambridge, pp 413–434, 2011), and the fact that the converted NGH product (which consists almost entirely of relatively pure natural gas and very low salinity water) will be at substantially lower pressures within the reservoir. Not only can pressure in the reservoir be controlled, but it is possible to maintain different pressures in different parts of the reservoir to better control dissociation and water and gas movement. A completely new, integrated approach to drilling NGH deposits is intended to optimize the opportunities presented by NGH deposits.