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Abstract. The Upper Devonian carbonate reservoir characterization of the Pamyatno-Sasovskoe Oilfield, Volgograd Region, Russia, is based on geological data, geophysical log, hydrodynamic and tracer investigations. The reservoir model based on geostatistical techniques with grid blocks has been used to update a flow simulation to available data on production history. The reliability of this reservoir model is lower because of the match to available data is unacceptable. The method to model permeability on the coarse scale presents the combination of the borehole radon indication and tracer investigation. According to tracing results, a streamline-based model is to be most realistic, gives a basis to propose the parameters and properties of streamlines and to predict the water-cut process.
Introduction. This study integrates geological data, geophysical log, hydrodynamic and tracer investigations to characterize the Upper Devonian carbonate reservoir of the Pamyatno-Sasovskoe oilfield, Volgograd Region, Russia. This oilfield is located in the northern part of the Volgograd Region, 300 kmnorthwest of Volgograd. This is the principal reservoir between the numerous platform margin reef buildups and it differs from other by concentrating reefs of different ages in the common buildup of 800 m in height. Reef reservoir consists of Frasnian fractured-dolomites and the relatively impermeable Famenian shale and limestone overlie it. The off-reef basin facies are shaly limestone which onlap against the reef.
In addition to the typical characteristics of carbonate reservoirs, Pamyatno-Sasovskoe reservoir is known for the following peculiar features:Considerable trending of the structure with length/width ratio exceeding 20:1 (fig.1);
Reservoir is isolated along of its outline;
Good vertical and lateral hydrodynamic communication despite high heterogeneity.
The reservoir model generated by geostatistical techniques with 220007 (151*31*47) grid blocks based on well-log and core data has been used to update a flow simulation to available data on production history. The reliability of this reservoir model is lower because of the match to available data on the production history is unacceptable.
A great volume of the reservoir studies has been carried out. Reservoir characterization is presented with the increasing of study scale, from rock samples to the reservoir as a whole: cores - geophysical characteristics - radon indication -tests - tracer investigation. Enlargement of the study scale shows the significance of the great voids of a carbonate reservoir. The "super fracture - super reservoir" zones connect all the wells into a single hydrodynamic system. Pressure in the various part of the pool is leveled off and there are no reasons for water conning. In such a case a system of great voids serves like a balancer and separator for the oil-water contact leveling in the vicinity of producing well.
According to tracing results, a model of a continuous super fracture going in parallel to the axis of the reservoir and connecting the west and east structure flanks seems t_ be most realistic (Fig.2). High velocity of tracer (tritium and some chemicals) along the axial part of structure gives a basis to propose the mainly linear flow from the injection well towards producing ones. The producing wells communicate with the injecting well along a system of super-fracture and smaller fractures, they can be considered as branches of the main fracture. Streamline properties can be evaluated by tracer velocity (travel-time), tracer concentration in producing water and frequency of tracer indices in the wells. The monitoring of producing water composition may support this evaluation. These data have been used to characterized streamlines from the injectors to producing wells to predict water cut process in every well.