engleski

Geostatistical Estimation and Simulation Approaches for More Detailed OGIP Calculations (Stari Gradac - Barcs Nyugat Field)

The paper describes improvements obtained by two different geostatistical approaches, which can often very successful deal with uncertainties in reservoirs. Porosity was selected as the most important parameter for reservoir quality determination. This parameter was one of four variables used as inputs in OGIP (Original Gas In Place) calculation. Each of these four variables previously were represented by four single maps (porosity, water saturation, gross thickness, net/gross thickness ratio), multiplied and expresses as "classical" OGIP result. Of course, each of these maps was characterised with more or less uncertainties, especially porosity and saturation maps, where it was impossible to include seismic controlling in inter-well areas. These maps are created only from maximal 16 average well (point) values. It is why two geostatistical approaches are applied to deal with such uncertainties. Calculations are performed with data collected on Stari Gradac-Barcs Nyugat gas field, separately for each of four reservoir lithofacies (named as Clastites, Dolomites, Quartzites and Metavolcanites). The gae of these lithofacies varies from Neogene (Badenian) to Palaeozoic. Contact water-hydrocarbon is unique for entire field. In first case (geostatistical estimation) variogram model of porosity is constructed and Ordinary Kriging mapping method is performed. New porosity maps are evaluated as more detailed and precise maps are evaluated as more detailed and precise than old ones, based on contour line shapes and cross-validation results. In second case (geostatistical simulation) Sequential Gaussian Simulation algorithm was used to achieve 100 porosity realizations. This model included same variogram model as well as Ordinary Kriging used in estimation. Set of 100 porosity maps represented outcomes, and base for 100 OGIP calculations (volumes). It was possible select "average" realization as well as minimum and maximum porosity maps regarding 2 standard deviations margins. Finally, different approaches and results of OGIP are compared. Advantages of geostatistical approaches are outlined and differences between estimation and simulation are described.

geostatistics; variogram; Kriging; stochastic simulation; OGIP; Stari Gradac

nije evidentirano