As the number of stages of hydraulic fracturing along the horizontal wellbore increases, the cost of fracturing starts to exceed the cost of drilling the well. Therefore, the issue of costs optimization for hydraulic fracturing in general become highly important problem. In this regard, for optimization calculations, it is necessary to operate with such important geometric characteristics of fracture as half-length and height of the fracture, which can be determined by logging, well-testing and micro-seismic studies. This paper analyzes all types of studies to determine the geometric characteristics of the fracture, except its width. Logging surveys, which have been carried out on vertical and inclined wells, allow to determine with some degree of accuracy the height of the fracture, provided that the conditions of applicability of these surveys considering well azimuth and inclined angle in the zone of fracturing & logging. Among the logging methods that have been applied to that kind of problem, the highest priority in terms of the reliability of the results obtained is given. Well testing allow us to determine the effective half-length of a fracture, but with some limitations. Micro-seismic studies allow comprehensively and in three-dimensional view to determine the configuration of a fracture in a orientational well or a system of fractures in a horizontal borehole to a certain degree of accuracy.

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The generalization of Hydraulic fracturing in West Siberia and the increase of job size over the recent year can impact the field development strategy. The correct estimation of the fracture dimension is critical to maximize the recovery factor of heterogeneous reservoir developed with water flood. Three main uncertainties exist: fracture height, half-length and azimuth. Commercial fracture models provide length estimate once a reliable estimate of height is known. This is evident for 2D model which requires a direct knowledge of the height but also for p3D model where the height is indirectly obtained from coupling stress profile and fluid flow. Fracture azimuth is traditionally provided by the horizontal stress anisotropy from open hole sonic logging. Unfortunately, in West Siberia at depth of 2500–3000 meters, there is negligible tectonic and open hole sonic dipole did not provide obvious fracture orientation. Fracture height growth affect mostly fracture job size and cost. Height growth has also shown to be a cause of premature wellbore screen out. Fracture half-length and orientation can have a significant impact on the effectiveness of pressure maintenance and flood efficiency. A review of world publication of direct fracture geometry measurement has shown the validity of seismic methods and tilt indicators for tight rock, such as carbonates and tight sandstone. However, all experiments on soft sandstones, such as found in West Siberian, have shown more limited results. Given the uncertainties in effective Fracture geometry and the negative impact that they could have on the field development, Rosneft decided to invest in a field research study denominated Fracture Geometry Investigation, to validate various method offered by the service industry. Two basic methods were tested and combined: wellbore logging and passive seismic. Wellbore logging is used to obtain an estimate of wellbore fracture height. It combines temperature log immediately after Minifrac or after Frac and Cased Hole Sonic Anisotropy (CHSA) which can be run at any time after frac. The direct estimate of fracture height is used to validate the result of a calibrated HF simulator using Net Pressure matching analysis. Passive Seismic monitoring (PSM) is used to obtain direct estimate of height, length and azimuth. PSM Acquisition must be done during hydraulic fracturing from the nearest well. The main goal of this study was to validate each method's effectiveness and to construct a calibrated fracture model for the particular reservoir under investigation. The results of this investigation will be used to optimize fracture design, pressure maintenance strategy and pattern orientation. Fields and Reservoir Description The Priobskoe field, one of the largest oilfields in the world, is located in Western Siberia. The reservoirs under production are part of Cherkashinskaia set of rock [1, 2] composed of shales, siltstones and sandstones. 90% of the production for the Priobskoe oilfield comes from AC-10, AC-11 and AC-12. The main focus of this paper is on the AC-11 and AC-12 formations, where production development and enhancement activities have started in 2000. The AC-11 formation consists of laminated oil saturated sandstone. The average permeability of AC-11 formation is 8mD, and the porosity is 13–16%. The average oil saturation is 50–60% with reservoir pressure at 248 bars. The AC-12 formation situated below the AC-11 is characterized by complex and aerial heterogeneous structure of several sandstone bodies, which complicates HF application. AC-12 is oil saturated highly laminated sandstone with shale streaks in between. The average permeability of AC-12 formation is 1 to 2 mD, and the porosity is 14–18%. The average oil saturation is 50–66%, and the reservoir pressure about 255 bars. Malobalykskoe field is a large oilfield of West Siberia with a majority of reserves (about 80%) concentrated in Achimovskaya, a formation from the Cretaceous period. Formation BS16–22 of Achimovskaya is well developed covering all the area and is represented by alternation of sandstones, siltstones and argillites. This reservoir is separated from upper layer by clay bed with thickness from 1.4 to 86 meters. A cross-section of BS16–22 formation shows from 8 to 23 permeable layers. Average number of such layers is 10.8 with about 2 mD permeability and initial reservoir pressure of 278 bars.

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