Abstract

The evolution of the fracture stimulation in the Novogodnee Field in Western Siberia is detailed in this paper. The target interval is the JV1 interval of the Jurassic formation. This is a highly productive interval producing at a typical pre-stimulation rate of approximately 70 ton/day (500 bbl/day) with a high volume of gas. Significant increases in the production rate can be achieved by the successful application of fracture stimulation. Unfortunately, this was not the initial case in the field because most of the fracture treatments screened-out early in the fracturing process.

Even though the initial fracture treatments did not achieve the designs results, they did yield important information. First, there were increases in production resulting from the fracture treatments, indicating there is significant potential of higher production from successfully performing fracture stimulation. Also diagnostic injections were performed prior to the main fracture treatment to measure the critical fracture parameters.

Therefore a project was initiated to perform a detailed analysis of these fracture treatments to understand the cause of the early screenouts. As a result of this study the fracture treatments were redesigned leading to successful completion of the fracture treatments. The proppant volumes successfully placed have been as high as 213 tons (470000 lbs) of proppant. This is a significant increase over the initial treatments that screened-out with an average proppant volume of 36 tons (80000 lbs).

The resulting production increase from the successful treatments has been significant. The folds of increase in productivity have increased from 1.9 on the fracture treatments with the early screen-outs to an average on 3.1 folds of increase on the recent wells. The highest productivity increase was 3.4. These folds of increased productivity have resulted is the equivalent post-stimulation production rates increasing from 130 tons/day (950 bbl/day) to 220 tons/day (1600 bbl/day). Well J is an injection well as part of the pressure maintenance program. Following the fracture treatment the injection rate of fluid volume is equivalent to 1000 tons/day (7300 bbl/day). If the interval had not been fracture stimulated the rate would have been significantly less.

Introduction

The geological section of Novogodnee field has three structural depositionional layers pre-Jurassic formation, an intermediate structural layer and sedimentary meso-neozoik layer. In the lower part of this section are layers which were formed by strongly dislocated metamorphized, Precambrian Paleozoic formations.

The Novogodnee field is very productive with fairly high permeability, averaging about 10 mD. The oil has a significant amount of gas 3200 m3/ton (540 scf/bbl). The interval is approximately 7 to 10 m (22 to 32 ft) of thickness. Oil viscosity in the reservoir conditions is 0.3 cp, water viscosity in the reservoir conditions is 0.28 cp, bubble point pressure is 304 ??? (4470 psi).

This field was very active with a number of drilling rigs and new wellbores. Therefore, it was the focus of a large capital investment because of the significant increased oil rates that could be achieved from the field. Unfortunately the initial fracture treatments did not achieve the design objective of increased productivity due to difficulties with proppant placement. These screen-outs were definitely caused by something formation related because they were independent of the Service Company, fracture fluid, proppant type, and perforation technique.

Figure 1

shows the typical log data for the Jurassic formation and the surrounding layers, including the Georgian Shale above the target interval.

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