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On the assessment of lateral range of the variograms

UDK: 553.98.001
DOI: 10.24887/0028-2448-2017-11-32-33
Key words: variogram, lateral range, sequential indicator simulation, permeability, wells
Authors: K.E. Zakrevskiy (Rosneft Oil Company, RF, Moscow)

One of the key points in the geological models building is the determination of the lithology ranges both vertically and laterally during sequential indicator simulation (SIS). For the correct assessment of the variogram ranges it is necessary that the distance between the points of observations was equal or less than the range of variability. At the exploratory stage the distance between the drilled vertical wells is very significant; this condition is fulfilled for observations in the vertical (pitch of observations of 0.2-0.4 m). During the evaluation of the lateral range, when the step of observing the exploration phase is about 2 km or more, the variogram analysis have some difficulty. This article discusses a method of obtaining rough estimates of the value of the lateral range in the low-density drilling field. There are various ways of the horizontal range estimating: using the wells of this field or of the analog field, using seismic slices of 3D survey, description and analysis outcrops for these sediments (literature), formed under similar conditions, multiple realizations. In addition to the above it is proposed to use a statistical method based on the use of statistical relationships between the lateral range value, which characterizes the variability of lithology, and geological characteristics of the studied sediments. To obtain statistical relationships between the lateral range and the geological characteristics of the studied sediments were collected about 150 geological models. In the result, it was found that a statistically significant relationship of the lateral range there is a vertical range and the average reservoir permeability. This allows us to calculate the approximate lateral range required when the lithology SIS builds in conditions when the distance between the observation points (wells) of comparable or greater of range.

References

1. Deutsch C.V., Geostatistical reservoir modeling, New York: Oxford University Press, 2002, 376 p.

2. Dubrule O., Geostatistics for seismic data integration in earth models, Tulsa: SEG/EAGE, 2003, 279 p.

3. Reynolds A.D., Dimensions of paralic sandstone bodies, AAPG Bulletin, 1999, V. 83, no. 2, pp. 211–229.    

One of the key points in the geological models building is the determination of the lithology ranges both vertically and laterally during sequential indicator simulation (SIS). For the correct assessment of the variogram ranges it is necessary that the distance between the points of observations was equal or less than the range of variability. At the exploratory stage the distance between the drilled vertical wells is very significant; this condition is fulfilled for observations in the vertical (pitch of observations of 0.2-0.4 m). During the evaluation of the lateral range, when the step of observing the exploration phase is about 2 km or more, the variogram analysis have some difficulty. This article discusses a method of obtaining rough estimates of the value of the lateral range in the low-density drilling field. There are various ways of the horizontal range estimating: using the wells of this field or of the analog field, using seismic slices of 3D survey, description and analysis outcrops for these sediments (literature), formed under similar conditions, multiple realizations. In addition to the above it is proposed to use a statistical method based on the use of statistical relationships between the lateral range value, which characterizes the variability of lithology, and geological characteristics of the studied sediments. To obtain statistical relationships between the lateral range and the geological characteristics of the studied sediments were collected about 150 geological models. In the result, it was found that a statistically significant relationship of the lateral range there is a vertical range and the average reservoir permeability. This allows us to calculate the approximate lateral range required when the lithology SIS builds in conditions when the distance between the observation points (wells) of comparable or greater of range.

References

1. Deutsch C.V., Geostatistical reservoir modeling, New York: Oxford University Press, 2002, 376 p.

2. Dubrule O., Geostatistics for seismic data integration in earth models, Tulsa: SEG/EAGE, 2003, 279 p.

3. Reynolds A.D., Dimensions of paralic sandstone bodies, AAPG Bulletin, 1999, V. 83, no. 2, pp. 211–229.    


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