Mobara Gas Field Research Articles

Pore-water mobility: Distribution of δ37Cl, 36Cl/Cl, 129I/127I and dissolved 4He concentration in the core drilled in the Mobara gas field, Japan

We measured 36Cl/Cl and 129I/127I isotope ratios, dissolved 4He concentrations, and δ37Cl to estimate the residence time and flow characteristics of pore water in rocks of the Kazusa Group in the Mobara gas field, Japan. We deduced a residence time of 0.28–0.85Ma for the pore water, based on a secular equilibrium value of 7.05±1.58×10−15 for the 36Cl/Cl ratio in Pleistocene strata of the gas field. Furthermore, the concentration of 4He corrected by the solubility equilibrium model in the pore water indicated that residence times varied from 0.09 to 0.62Ma from the depth of 642 to the depth of 1742m in the core drilled in the gas field. The pore-water dating results have insignificant differences between the ages of the Kazusa Group formations, compared with the iodine ages from 129I/127I ratio. Variations of δ37Cl in the pore water suggested that mass transport in rocks of the Kazusa Group was dominantly controlled by diffusion.

The source and behavior of iodine dissolving in groundwater in the Mobara gas field

The source and behavior of iodine dissolving in groundwater in the Mobara gas field

Investigation of natural gas behavior in shallower geologic strata: Natural analogue of leaked gas in the Mobara gas field, Japan

Abstract To observe a natural analog of geologically sequestered CO2 leakage to the land surface, geological, geohydrological, and geochemical surveys have been conducted on gas seepage from the Pleistocene sedimentary rocks in the Sugaya area in the Mobara gas field, East Japan. In the resulting model, gas that separated from groundwater in the shallow part was stored by a fault trap and seal layer and then leaked via inclined sandstone layers, open cracks near the surface, and dragged sandstone in the fault damage zones.

Natural gas behavior in shallow geologic layers as natural analogues of discharge of CO2

Abstract In order to obtain public agreement on carbon dioxide (CO2) geological sto rage, it is required to assess the impact of leaked CO2 to our environment and dispel the anxieties as well as to d emonstrate technically the long-term stability of the geological CO2 storage system. As an essential issue to the assessment of the impact w e should understand CO2 behavior in sh allow geologic layers. From this point of view the authors carried out an inv estigation on natural gas behavior in shallow geologic layers in the vicinity of a natural gas reservoir as one of natural analogues of the behavior of leaked CO2 arriving from the deep storage layer. In this report the authors introduce the scheme of the investigation and the currently obtained results of the natural analogue study. The scheme of the investigation aims proposing the procedure to predict the movement of CO2 in shallow geologic layers, that is to say, geological surveying, numerical modeling, computing and estimating the impact of the CO2 to our living environment. The surveyed area is located in the Mobara gas field near Tokyo, Japan. It is said that the natural gas is dissolved in the brine in the turbidite sandstone layers of Pliocene-Pleistocene at the depth more than 200 meters below sea level. The land area is utilized as rice field and we can observe the spotted natural gas gushing when the rice field is filled with water. In this area the authors performed the exploratory investigation, borehole logging, electrical prospecting, underground radio detection, isotope analysis as well as natural gas flux measurement. They also studied the gas movement in the shallow layers by means of numerical analysis. The results of these efforts are briefly described as follows: The natural gas is not biologically originated near the surface but comes from rather deeper zone. The i mpermeable clayey layer traps the natural gas in gaseous phase and the geological structure such as faults and formations of the sedimentary layers restricts the footprint of the discharge of natural gas at the surface.

茂原型水溶性ガス田の産出挙動における毛細管圧力と浮力の働きについて

The Mobara gas field is one of the dissolved-in-water type natural gas fields. This field exists in Chiba Prefecture, Japan. The wells in this field have particular production performance curves called “Mobara type”. The gas water ratio curves are initially low, and then increase to be so high as to blow up a large amount of water.The Mobara gas deposit consists of alternate layers of sandstones and mudstones. We applied mud logging to exploration of the Mobara gas deposit. As the result, a small amount of free gas was detected in the mudstones.In addition to exploration, we carried out laboratory experiments using an X-ray CT scanner and mudstone cores. In the experiments, gas and water flow rates and CT values were measured at the same time. Gas water ratio increased with incremental drop of pore pressure, and gas saturation calculated from CT values also increased.From analyzing the exploration and the experiments, following conclusions were obtained.(1) In the Mobara gas deposit, gas bubbles of extremely small size are stored in pore bodies of the mudstones.(2) Upward buoyancy forces and downward forces given by capillary pressure difference act on gas bubbles at all times. These forces are initially in equilibrium.(3) With the start of production, hydraulic gradients occur and capillary pressure actions change in mudstones. The gas bubbles begin to move through pore throats toward sandstones consequently.The above-mentioned experiments suggest that buoyancy and capillary pressure have an important effect on the Mobara type production performance.

千葉県茂原ガス田の地下地質と水溶性天然ガス・ヨウ素の生産性について

千葉県茂原ガス田の地下地質と水溶性天然ガス・ヨウ素の生産性について

茂原ガス田の産出挙動と毛細管圧力の関係について

The reservoir of the Mobara gas field is restricted to the Kazusa group which is a sedimentary basin made up of sandstones and silty mudstones alternately. It was understood that the Mobara gas reservoir is a dual porosity type. We developped a mathematical model that is useful in simulating the Mobara type performance.Most of the gas generated in the mudstones is dissolved in the brine reserved in the both rocks. A little of the gas is distributed as discontinuous globules due to pore throats in the silty mudstones.The bubbles begin to move toward the sandstones when the formation pressure has been reduced. In this mechanism the rock properties are important, especially relative permeability and capillary pressure. Because the mobility of gas phase becomes better by far as compared with that of water phase, the gas water ratio increases continually.

MICROBIOLOGICAL STUDIES ON PETROLEUM AND NATURAL GAS

Microbiological studies on the Niigata and Mobara gas-fields in Japan were carried out. A considerable number of aerobic bacteria, mainly belonging to genus Pseudomonas, were isolated from the gas-brines of a depth of 300m to 800m, but few or no microorganisms were found in depth over 1, 000m. Taxonomic studies revealed that a succession in the microflora took place in the gas wells during the three years from only a few microorganisms to a large number of pseudomonads of the fluorescent group. It was deduced from these facts that large amounts of fresh water may invade into the gas-layers from the outside, and that the water may flow from the north-east to the south-west in the Niigata gas-field. In comparison with the oil-brines, it was interesting that no kerosene-utilizing bacteria or anaerobic sulfate-reducers were found in the gas-brines in the Niigata gas-field. No microorganisms were found in the gas-brines in the Mobara gas-field. The use of bacterial tracers for natural gas mining, as well as for petroleum mining, is suggested.

MICROBIOLOGICAL STUDIES ON PETROLEUM AND NATURAL GAS

Microbiological studies on the Niigata and Mobara gas-fields in Japan were carried out. A considerable number of aerobic bacteria, mainly belonging to genus Pseudomonas, were isolated from the gas-brines of a depth of 300m to 800m, but few or no microorganisms were found in depth over 1, 000m. Taxonomic studies revealed that a succession in the microflora took place in the gas wells during the three years from only a few microorganisms to a large number of pseudomonads of the fluorescent group. It was deduced from these facts that large amounts of fresh water may invade into the gas-layers from the outside, and that the water may flow from the north-east to the south-west in the Niigata gas-field. In comparison with the oil-brines, it was interesting that no kerosene-utilizing bacteria or anaerobic sulfate-reducers were found in the gas-brines in the Niigata gas-field. No microorganisms were found in the gas-brines in the Mobara gas-field. The use of bacterial tracers for natural gas mining, as well as for petroleum mining, is suggested.

Recent Development of Mobara Gas Field with Special Reference to its Production Performance

In the Mobara gas field, production and gas water ratio histories of the Umegase and Otadai formations are highly indigenous, as compared with the neighbouring fields. The initial gas water ratio starts at 3-4, but after considerable cumulative water production, the gas water ratio rapidly increases up to 10, or, in some cases, higher than 300. The cause of this peculiar performance may be derived from the following reservoir conditions. 1) Low permeability. 2) Initial gas water ratio is higher than solubility at reservoir pressure and temperature. 3) Shallow depths of reservoirs. 4) Frequent alternation of sand stone and mudstone. 5) Abundant faults. In this paper, concerning above mentioned five conditions, the areal limitation of the reservoirs with this peculiar performance is discussed.

About the Utilization of Plastic Pipe to Gas Wells in Mobara Gas Field, Chiba Prefecture, Japan

In the traditional method of well completions in gas fields of gas dissloved in water type, the steel casing pipes were utilized in almost cases. The steel pipes had feen corroded quickly by producing water from gas wells. For the two purposes, the prolongation of well lives and the low cost of well completions, writers had researched and tested about the utilization of plastic pipes. (poly vynil chloride pipe) And writes suceeded in completion of many natural gas wells using plastic pipes in Mobara gas field, Chiba prefecture. From the experiences of actual works of well completion, writers shall explain about the following itens in the report. (1) On the characters of PVCP (poly vynil chloride pipe) utilized in casing pipes. (2) On the economy of well completion with PVCP casing. (3) On the practices of utilization of PVCP. (4) On the results of the test of strength of PVCP.

Estimation of Gravity Drive in Mobara Gas Field and Some Conditions for its Development

In 1952 the author described that the performance behavior of Mobara gas field was the results of gravity drive in the report The Development of Mobara gas field. In this report some more details are explained.The most significant characters of the Mobara reservoirs are generally not very well understood because of the complexities. To explain these conditions in somewhat more detail, it is necessary to use the performance curves in the field being now developed.On gravity drainage, counter-current flow of gas up-dip may become important factor. When water drains down-structure it must be replaced by gas.So that wells high on structure show increase of gas water ratio more rapidly than wells low on structure.The M. E. R. (most efficient rate of production) is about 15, 000-20, 000 m3 gas per day per6, 000, 000 square meters in the case of which water level declines 6 meters per year.

Acidizing at Mobara Gas Field

Acidizing at Mobara Gas Field

Study on the Design of Gas Lift Well

When the present writers designed a gas lift installation, they depended on the past experience. Because they have many variables involved in making gas lift calculation. The study of continuous flow gas lift well by F.H. Poettmann and P.G. Carpenter made it possible theoretically to design gas lift installation. The gas lift system is actually in practice at Niigata gas field, Mobara gas field and many other gas fieleds in the country. If writers can apply their theory to designing gas lift well in the gas fields of Japan, the efficiency of gas production from the wells may be increased. The most common type of gas lift method at the gas fields is one in which the gas is injected into tubing and the production returned through the annulus. They studied the gas lift method in which the gas was injected in the annulus and the production returned through the tubing, and the the correlation curve, though essential in their theory, can not be extended to flow through casing size. Making the application of their method, writers must study whether writers can use their method or not.Writers carried out the gas lift tests, in which the gas was injected into the tubing, at 6 inches water well drilled in the Akita University field. The results from the tests were the same as those obtained from the calculation based on their theory. (see Fig. 2) It became clear that their theory could be extended to the gas lift in which the gas was injected into tubing. And writers calculated the correlation factors from the data collected at Niigata gas field, and a plot of the correlation factors versus the product of the hydraulic radius of the annulus and the mass velo city of the fluid is shown in Fig. 3. By using the correlation curve, writers may desigen the gas lift wells in Niigata gas field and may increase the efficiency of the gas production from wells.

On the Study of the Relative Permeability in the Mobara Gas Field

The objects of this investigation are the measurements of relative permeability of the sands in Mobara Gas Field and the improvements of the technique and apparatus used on the experiments. The results obtained from the experiments are given on Fig. 3 and Fig. 4. Fig. 3 shows warer permeabilities in thecase of very low value, but the writers have not enough data to explain on the factors affecting on the low values.

On the Core Analysis of Natural Gas Exploration Well, Chiba R-1

Recently in Japan the methane gas, of which geological occurence is free from petroleum, has been utilized. Except some cases, the gas is dissolved into formational water according to hydro-static pressure-temperature relation. The writer describes the result of the core analysis of exploration well for natural gas of this kind in this paper. The formational water dissolving natural gas under the reducing condition may be teken the place or degenerate by the invasion or diffusion of meteoric water along the permeable sediments, and consequently the gas potentiality may decline. The chemical analysis of the interstitial water of core may indicate the influence of the meteoric water and detect the vertical distribution of gas potentiality. In practice, this method is a application of usual methodology of “geochemical survey by underground water” to the interstitial water of muddy core. Chlorine may be a factor of chemical environment atf deposition and slso the measure of the destructive process by meteoric fresh water. Its concentration well shows the vertical change of the destructive process together with the values of long normal curve of electric logging. Ammonium and bicarbonate may be tne measure of potentiality as the products of the same phase of formation _??_ destruction equilibrium of gas. Furthermore, ammonium may be a measure of the destructive process by metheoric water as well as chlorine. The presence of nitrite and nitrate shows decidedly the characteristics of meteoric water of oxidative status. The consumption of potassium permanganate reaches the first peak at the contact zone of connate and meteoric water, where the intersticial water is dark brown-colored by humic matter, and again becomes larger downwards, where the interstitial water is colorless. The similar phenomenon is known horizontally within the Mobara gas field. But the absolute value is far higher in the core analysis. This may be caoused by the condition (especially pH) at the extraction of interstitial water. By the micropaleontological study of core, the gas bearing formations may be the Plio-Pleistocene sediment of lower neritic deposition. In the vicinity of the Mobara gas field, these formations are invaded by meteoric water, having no gas potentiality.

正誤表

正誤表

Discussion on the Geologic Survey Method used on the Mobara Gas Field in 1949

The methods used in 1949 by geologists of the Oil Section of the Geological Survey of Japan for the survey of the Mobara Gas Field, Chiba Prefecture, are discussed. The writer believes that the primary objective in the stratigraphic study of sedimentary deposits should be the determination of the true relation between the strata and the time planes. The writer recommends that the distribution of the following four elements should be shown on geologic maps of sedimentary basins : (a) Lithologic types ; (b) time planes (indicated by such markers as tuff beds); (c) macrofossil facies; (d) microfossil facies. The combination of elements (a) and (b) indicates the relation of the mappable lithologic units to the time of deposition, and elements (c) and (d) indicate the environment of deposition.

On Natural Gas Geology of the Western End Area of the Mobara Gas Field, Chiba Prefecture

On Natural Gas Geology of the Western End Area of the Mobara Gas Field, Chiba Prefecture

The Development of Mobara Gas Field

The Development of Mobara Gas Field