Abstract

To continue effective development requiring alteration of waterflood system and reduction of risks associated with infill sidetrack drilling of UV1 formation of Varingskoe oil field in Western Siberia, which is characterized by high water cut and presence of confirmed technogenic fracturing we developed a procedure using analysis of production and well-log data for identification of technogenic fracture zones and their lateral and vertical extent.

The analysis of lateral technogenic fracturing distribution is based on a method of statistical evaluation of injection wells influence on production wells rates using Spearman rank correlation. According to the analysis and the results of additionally performed tracer injection test and special core analysis determining the principal stress axes on core samples we determined zones in which technogenic fracturing substantially adds to water cut of producing wells and principal directions in which fracturing takes place for each producing well.

To assess the confinement of technogenic fractures to any reservoir interval we compared wells which have tight impermeable layers within productive strata and ones that lack them with fractures identified statistically.

Using statistical analysis we identified for each production well the direction of fracture propagation with qualitative assessment of intensity of fracture role in fluid flow in that direction, with the preferred orientation being subparallel to low-amplitude tectonic faults coinciding with the principal directions of the stress tensor determined on core samples.

A joint analysis of technogenic fracture map and distribution of tight non-permeable layers within producing intervals allowed to determine a strong correlation (central northern part of the reservoir) between the lack of these tight layers and low Spearman rank correlation coefficient, which indirectly points to the relation between tight, conductive layers (as a result of plastic deformation and subsequent fracturing) and high fluid flow rates.

Analysis of production data using this algorithm helps in determination of lateral and vertical fracture distribution for subsequent analysis and alteration of waterflooding system as well as correction of injection profile, risk reduction in determination of remaining mobile oil reserves areas and planning of new wells based on realistic fluid flow models.

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