December 1, 2008
Advanced Search

Login:

Password:

Forgot your password?
Register now

Home / Issue Archive / 2006 / July #7 / Studying Geology, Geophysics of Severo-Urengoy from Space

№ 7 (July 2006)

Studying Geology, Geophysics of Severo-Urengoy from Space

In the Severo-Urengoy field, VNIIGAZ performed a lineament analysis of the space sounding data and consequent comparison of the space, geological and geophysical, and also field-geological materials.

By Yuri Baranov, Dmitry Lyugay, Yuri Kantemirov

Share it!
The technology for integrated space-geological-geophysical investigations (SGGI) made a technical basis for the studies performed; this technology was developed at the VNIIGAZ laboratories based on the directives of the RF Ministry of Natural Resources and Gazprom. SGGI were aimed at solving the following problems:

• To map multiple-rank lineaments (projections of deep faults to the earth surface) of different trends;
• To investigate the character and degree of geodynamic activity of identified lineaments at the modern stage of the geological development on the basis of the comparative analysis of the results of the space-geological-geophysical investigations;
• To perform retrospective space monitoring of the geodynamic activity of the area under study (using materials of the period from 1987 to 1999);
• To calculate lineament density for various trends;
• To analyze the effect of the tectonic dislocations on the intensity of the water encroachment of the Cenomanian gas pool and to optimize the designed location of separate wells and well clusters on the basis of the obtained results.

To solve the above indicated problems, satellite space image of medium resolution (60 m) was used as initial data of the space sounding of the Severo-Urengoy field, this image was received from satellite Landsat-7 by sensor ETM+ (Enhanced Thematic Mapper Plus) on August 07, 1999. Partial reinterpretation of the historic geophysical and field-geological materials on the Severo-Urengoy field was performed. All space-geological-geophysical data were geo-positioned in the Gauss-Krueger conformal projection on the Krasovsky's ellipsoid in Pulkovo-1942 coordinate system and were integrated into the geo-informational system.

Lineament analysis of the above indicated space photo (thermal range of electromagnetic spectrum, sounding wave length - 10.4-12.5 m, spatial resolution - 60 m) was done in WinLessa 2.1 software.
The identified lineaments, complicating the geological structure of the Severo-Urengoy field are shown in Fig. 1. The fact that lineament deconsolidation zones are confirmed by the data of three independent methods (seismic, field geophysics and decoding of space photos) proves objective character of the received results. Faults identified by the seismic survey data in the Neocomian appear on the earth surface in the form of lineaments. Therefore, the Cenomanian deposits are also affected by them. These faults in the Cenomanian deposits appear in the form of deconsolidation zones which disrupt integrity of clay interlayers and, in this way, affect the rate of vertical intrusion of the bottom and edge water into the pool.

Comparison of the map of faults of the north-eastern direction with the map of the original gas-water contact of the Cenomanian pool (Fig. 2) enabled us to make a conclusion that orientation of the gas-water contact prior to the Severo-Urengoy field development followed the trend of "a-a" fault established both by the data of the seismic survey in the Neocomian deposits and by the results of decoding of the Earth surface space photos.

The results of the retrospective space monitoring of the geodynamic situation in the western dome of the Severo-Urengoy field showed that the consequent development of the pool activated the system of dislocations having the same direction as "a-a" fault. Man-caused activation of this system of dislocations was established by the results of the comparative analysis of two non-simultaneous space images obtained with identical cameras.

To visualize the results of monitoring of the dislocation systems' activity, a rose diagram of lineaments (revealing their most pronounced directions) was built for each photo. Rose diagrams of lineaments built for both photos illustrate maximum intensity of the lineaments of the north-eastern and north-western trends. It should be noted that the development of the Western dome of the Severo-Urengoy field affected activation of the dislocation system of the north-eastern trend. To estimate numerically activation of dislocation system of the north-eastern trend, a parameter of rose diagram axes' contrast (ratio of the length of the longer axis to that of the shorter one) was selected. This parameter seems to be an optimal one for the given case, as only two directions are pronounced in the both rose diagrams. The rose diagram built for the photo of 1987 is characterized by contrast of axes equal to 1.18 in the north-eastern direction. The contrast of axes in the rose diagram built for the photo of 1999 reaches 2.0 in the same direction. The relationship of these two contrast parameters shows that the geo-dynamic activity of the dislocation system of the north-eastern trend increased 1.8 times during 12 years of development (1987-1999).

The results of analysis of the lineaments and their man-caused activation in time enabled us to make a conclusion on the dominant effect of the dislocation system of the north-eastern trend of the same direction as the "a-a" fault on the intensity of vertical fluid flows. Comparative analysis of the identified lineaments with the map of the current (as on January 01, 2005) gas-water contact of the Cenomanian pool showed correspondence of the north-eastern orientation of the gas-water contact rise dome to the trend of the "a-a" fault.

The effect of deconsolidation zones on the rate of water encroachment of the Cenomanian pool is further illustrated by the most statistically verified integral parameter - density of lineaments of the defined trends. The results of density calculation for lineaments direction are shown in Fig. 5. It is clearly seen that peaks of density of lineaments having the indicated direction correspond to the areas of the maximum rise of the gas-water contact, and density minimums correspond to the areas with low rate of the gas-water contact rise.

It should be noted that original gas-pool outline coincides with the gradient boundaries of densities of the lineaments of the indicated trend. As the gas-pool outline is confined mostly to the areas of extremely high density of lineaments (i.e. to the areas of the maximum dislocation by the faults of the given trend), we can make a conclusion that the data of space sounding showed the pronounced boundaries of the Cenomanian pool structure, to which the gas-pool outline is confined.

Analysis of SGGI results enabled us to formulate a general conclusion on the highest modern geodynamic activity of the system of faults having north-eastern trend, which agrees with the general geodynamic situation in the region. Compression affecting the Urengoy bar from the east and west "closes" faults of sub-meridional trend; at the same time, sub-latitudinal faults parallel to the regional stress vector remain open and actively affect vertical gas and water cross-flows and, consequently, rates of water encroachment of the Cenomanian pool of the Severo-Urengoy field. Mapped geodynamically active faults of north-eastern trend and in particular, "a-a" fault are classified by the authors as local realizations of the transformed trans-regional Charlie fault in the zone of its geodynamic influence. It should be noted that at present additional horizontal rock displacement is taking place along the axis of the Charlie fault.

On the whole, based on the SGGI results, effect of the tectonic dislocation of the geo-environment (alongside with its lithological features) on the rate of water encroachment of the Cenomanian pool in the Severo-Urengoy field was established. The proposed approach agrees well with the existing concepts of the Cenomanian pool water encroachment. Thus, according to the opinion of many researchers, occasional, not consistent area-wise or section-wise spread of clay interlayers occurs in the Cenomanian deposits. Generally impermeable clay interlayers obtain vertical permeability in case of their tectonic dislocation. Thus, within the mapped deconsolidation zones, average vertical permeability increases; this explains acceleration of vertical advance of the formation water in these zones. As for the edge zones, here it is necessary to take into account the possibility of advanced water encroachment along the bedding (selective water encroachment of highly permeable reservoirs).

Received results, by way of example of the Cenomanian pool of the Severo-Urengoy field, proved the efficiency of integrated space-geological-geophysical investigations, which enables us to recommend these investigations to be performed on all fields of the Big Urengoy.
Share it!
/
Copyright © 2008 Eurasia Press, Inc. (USA). All rights reserved.
Web programming by Iflexion
Copyright © 2008 Eurasia Press (www.eurasiapress.com)