Gas Storage Site Research Articles

The effect of local distortions on time‐domain electromagnetic measurements

Based on the time‐domain integral equation, we derive expressions for the effect of an anomalous body close to the receiver or close to the transmitter on transient electromagnetic measurements. Similar to magnetotellurics, the distortion of electric fields at late times can be described by a constant distortion tensor relating the secondary electric field to the primary field components that would be obtained in the absence of the body. The distortion of a single electric field transient is a static shift only for particular configurations over a layered half‐space. In the general case, the perturbation is time dependent because the direction of the total electric field vector varies with time. The theory nicely explains spatial variations in electric field transients measured during a high‐redundancy long‐offset transient electromagnetics (LOTEM) survey over an underground gas storage site. An inversion example with synthetic data illustrates how distortion can be corrected. The elements of the distortion tensor are determined simultaneously with the model parameters. Ambiguity is reduced by a regularization of the distortion parameters. In the example, the background model is recovered well, even for the difficult case where only one transmitter is used. The distortion of the magnetic field time derivatives caused by bodies close to the receiver is proportional to the time derivative of the primary electric step response. The distortion is generally not limited to early times and cannot be neglected in general. Transmitter overprint effects resulting in static shifts of vertical magnetic field time derivatives may also be understood from the theory.

High-resolution characterization and integrated study of a reservoir formation: the danian carbonate platform in the Aquitaine Basin (France)

This paper provides an example of an integrated multi-scale study of a carbonate reservoir. The Danian Lower R2 carbonate reservoir is located in the South of the Aquitaine Basin (France) and represents a potential underground gas storage site for Gaz de France. The Danian Lower R2 reservoir was deposited as a prograding carbonate platform bordered by a reef barrier. The effects of sedimentary and diagenetic events on the reservoir properties, particularly dolomitization, were evaluated. In this study, the reservoir quality has been assessed by seismic analyses at the basin scale, by log-analysis at the reservoir scale, by petrographic methods and by petrophysical tools at the pore-core scale. Two dolomitization stages, separated by a compaction event with associated fracturing and stylolites, have been identified. These diagenetic events have significantly improved the Lower R2 carbonate reservoir properties. It is demonstrated that the reservoir quality is mainly controlled by the pore-geometry, which is determined by various diagenetic processes. The permeability values of the reservoir range over 4 orders of magnitude, from 0.1 to 5600 mD and the porosity values range between 2 and 42%. Reservoir unit 4 (a karstic dolomite) shows the best reservoir properties with average porosity values ranging between 11.1% and 19.3% and an average permeability ranging between 379 and 766 mD. Reservoir unit 2 (a fine-grained limestone) shows the worst reservoir properties. The cementation factors range from 1.68 to 2.48. The dolomitic crystal carbonate texture (mainly units 3 and 4) shows the highest value of the cementation factor (1.98–2.48) and formation factor (9.54–36.97), which is due to its high degree of cementation. The saturation exponents vary between 1.2 and 3.4. Using these experimental electrical parameters and the resistivity laterolog tool we predicted the water saturation in the various reservoir units. The permeability was predicted by combining the formation factor with the micro-geometric characteristic length. The best fit is obtained with the Katz and Thompson's model and for a constant of 1/171.

The geology and geophysics of the SW Kinsale gas accumulation

Abstract The SW Kinsale gas accumulation is located in blocks 48/20 and 48/25 in the North Celtic Sea Basin, 50 km off the south coast of Ireland. The field lies in c. 100 m of water. The discovery well, 48/25-2, was drilled in 1971 and encountered gas-bearing fluviatile sandstones in the Lower Cretaceous Wealden sequence. In 1995, well 48/25-3 was drilled close to the discovery well on the southwestern limb of the Kinsale Head anticline, which is thought to have formed during Tertiary basin inversion. The well data indicate that this southwestern area is in pressure isolation from the main Kinsale Head Field, which lies in the central and eastern sectors of the structure. In 1997 a 3D seismic survey was acquired to assess the suitability of the field as a potential gas storage site. These data suggest that SW Kinsale is in structural isolation from the main Kinsale Head Field. Mapping of the 3D volume reveals SW Kinsale to comprise a relatively simple low-relief anticline. There is c. 160 m of closure from −810 m true vertical depth sub-sea (TVDSS) at its crest to −968 m TVDSS along a syncline to the north. The accumulation is thought to have a shared gaswater contact with the main Kinsale Head Field at −945 m TVDSS, beneath which lies a transition zone to −968 m TVDSS. The area within closure is close to 1200 ha. These data also suggest that the reservoir has undergone a minimal degree of structural compartmentalization. A major Wealden channel axis is interpreted to transect the field. Southwest Kinsale is thought to contain 1.1–1.4 BCM (billion cubic metres) gas initially in place with about 0.85 BCM recoverable. The field was recently developed as a single well sub-sea tieback to the Kinsale Bravo platform. First gas deliveries from the field took place in late 1999.

A first attempt at monitoring underground gas storage by means of time‐lapse multichannel transient electromagnetics

Two successive transient electromagnetic surveys were carried out over an underground gas storage site in France. The idea was to monitor changes in the gas bubble from the differences in the data. If successful, the new methodology could help to reduce the number of monitoring wells and finally reduce costs. Preliminary 3D modelling indicated that the resistivity changes caused by movements of the gas/water contact should be detectable in the electric field transients provided that the signal‐to‐noise ratio is at least 100:1. The surveys were performed with the TEAMEX multichannel acquisition system, adapted from a seismics system. The highly redundant data were analysed by calculating the relative differences in the electric field transients. The differences were common‐midpoint‐sorted and spatially stacked. Another approach was the calculation of electric field time derivatives in a log–log domain, to eliminate static shift effects which are present in the data. Even though the data quality is excellent from a classical point of view, neither of the two approaches reveals changes in the data which might be caused by changes in the gas reservoir. In future applications to monitoring, transmitters and receivers should be installed permanently, and the transmitter input waveform should be monitored continuously, to avoid some of the problems encountered here. Moreover, the signal‐to‐noise ratio will have to be further increased by at least one order of magnitude.

Development of a model to predict the effects of explosions in compact congested regions

In this paper it is shown how a number of models can be produced and linked together to predict the consequences of a vapour cloud explosion in a compact region of congestion on a typical gas processing or storage site. The individual models address the generation of pressure within the congested region, the propagation of the resulting pressure wave away from the region and the load received by any obstacle on the site outside of the congested region. The performance of each of the models is illustrated and discussed, including comparisons with experimental data. Finally, the application of the models to practical cases is considered.

Underground gas storage sites: their purpose, their equipment and their exploitation (in French) : Lecoanet, A; Blondin, E; Giminez, J Industrie MineraleV71, Jan 1989, P42–49

Underground gas storage sites: their purpose, their equipment and their exploitation (in French) : Lecoanet, A; Blondin, E; Giminez, J Industrie MineraleV71, Jan 1989, P42–49

The performance of water curtains surrounding rock caverns used for gas storage

This study aimed to clarify the effects of water curtains for pressurized storage of gas in unlined rock caverns. Geological and hydrogeological data from an actual gas storage site in Sweden are presented, as well as results from performance tests carried out using compressed air within the caverns. Calculations obtained by various theoretical methods of flow analysis are compared with actual flows taken from the caverns. Long-term operational data are also used for comparison.

Oil and Gas Developments in North Mid-Continent in 1976

Crude oil production in Kansas during 1976 (58,714,198 bbl) was 0.66% below the 1975 level; natural gas production (836,205,709 Mcf) decreased 1.7%. Processing plants recovered approximately 28 million bbl of natural gasoline and LPG products, and 537 MMcf helium. Drilling increased 17%, with 3,977 holes; 54.3% of the holes drilled solely for oil or gas were successful. Minnesota has a unique noncommercial well that produces from middle Precambrian rocks. Its brine contains lithium and zinc, and gas from the well has an abnormally high argon content. No tests for oil or gas were drilled in the state in 1976. Missouri's drilling was 50% below the 1975 level, with 45 completions. Shallow core testing continues in western Missouri. Nebraska's drilling occurred in all 4 produ ing basins; the 323 completions were only 7% below the number of wells drilled in 1975. Kimball and Hitchcock Counties had the most activity, with 66 and 65 compeltions respectively. No tests were drilled for oil, gas, or gas-storage sites in Iowa or Wisconsin during 1976.

Developments in Indiana in 1961

Indiana's oil production for 1961 totaled an estimated 11,460,000 bbls., a decrease of approximately 594,000 bbls., or 5% from the 1960 production. The total number of wells drilled decreased from 1,072 in 1960 to 788 in 1961, a drop of nearly 27%. Of the 788 total wells drilled, 246 were wildcat wells and 542 were field-development wells. Thirty of the wildcat wells were successful, 12 being completed as new pools, 10 as extensions to pools, and 8 as new pays in productive areas. Twenty-four successful wildcat wells were completed in rocks of the Mississippian System, 2 in the Devonian, and 4 in the Ordovician. Pennsylvanian and Mississippian formations of southwestern Indiana continued to be the principal objectives of exploratory drilling. Successes in Chester reservoirs in southeastern Pike County were significant. These successes indicate that the area of shallow Chester reservoirs throughout eastern Pike County, southern Daviess County, and Dubois County is worthy of further exploration. Exploration for underground gas storage sites continued during 1961. Stratigraphic units tested include Devonian, Silurian, Trenton, and Knox strata.