**Key words:** oil rims, critical production rate, horizontal wells, optimal well spacing.

The paper describes the novel method to estimate cost effective oil thickness for oil rims and oil reservoirs with gas cap. The method is bases on analytic solutions for critical well oil production rate (critical – without production of breakthrough gas) during early regime of vertical displacement and late regime of gravity drainage. Based on the analytic solution, we propose a dimensionless technic and economic parameters that determine optimal, that maximize Net Present Value, well spacing. The dimensionless parameters include oil thickness, permeability, oil density, initial and residual oil saturations, well costs, oil prices. Given optimal well spacing, we propose an analytic criterion of estimation of cost-effective thickness.

References

1. Giger F., Low permeability reservoirs development using horizontal wells,

SPE/DOE 16406, 1987.

2. Masoudi R., How to make a magic change and get the most out of your oil

rim reservoirs, 2011. – http://www.spe.org/dl/docs/2012/masoudi.pdf

3. Sobocinski D., Cornelius P., A correlation for predicting water coning time,

JPT, 1963, pp. 594-600.

4. Kuo M., Des-Brisay. A simplified method for water coning predictions,

SPE 12067, 1983.

5. Wheatley M., An approximate theory of oil/water coning, SPE 14210, 1985.

6. Chaperon I., Theoretical study of coning toward horizontal and vertical

wells in anisotropic formations: subcritical and critical rates, SPE 15377, 1986.

7. Giger F., Analytic two-dimensional models of water cresting before breakthroughfor horizontal wells, SPE, 1989, pp. 409-416.

8. Dikken B., Pressure drop in horizontal wells and effect on production performance, JPT, 1990, pp. 1426-1433.

9. Suprunowicz R., Butler R., Vertical confined water drive to horizonsl well-

Part1: water and oil of equal densities, Journal of Canadian Petroleum Technology,

1992, no. 3, pp. 39-47.

10. Khasanov M.M. , Ushmaev O.S., Samolovov D.A. et. al. A Method To Determine Optimum Well Spacing for Oil Rims Gas-Oil Zones. SPE 166898. – 2013.

**Key words:** oil rims, critical production rate, horizontal wells, optimal well spacing.

The paper describes the novel method to estimate cost effective oil thickness for oil rims and oil reservoirs with gas cap. The method is bases on analytic solutions for critical well oil production rate (critical – without production of breakthrough gas) during early regime of vertical displacement and late regime of gravity drainage. Based on the analytic solution, we propose a dimensionless technic and economic parameters that determine optimal, that maximize Net Present Value, well spacing. The dimensionless parameters include oil thickness, permeability, oil density, initial and residual oil saturations, well costs, oil prices. Given optimal well spacing, we propose an analytic criterion of estimation of cost-effective thickness.

References

1. Giger F., Low permeability reservoirs development using horizontal wells,

SPE/DOE 16406, 1987.

2. Masoudi R., How to make a magic change and get the most out of your oil

rim reservoirs, 2011. – http://www.spe.org/dl/docs/2012/masoudi.pdf

3. Sobocinski D., Cornelius P., A correlation for predicting water coning time,

JPT, 1963, pp. 594-600.

4. Kuo M., Des-Brisay. A simplified method for water coning predictions,

SPE 12067, 1983.

5. Wheatley M., An approximate theory of oil/water coning, SPE 14210, 1985.

6. Chaperon I., Theoretical study of coning toward horizontal and vertical

wells in anisotropic formations: subcritical and critical rates, SPE 15377, 1986.

7. Giger F., Analytic two-dimensional models of water cresting before breakthroughfor horizontal wells, SPE, 1989, pp. 409-416.

8. Dikken B., Pressure drop in horizontal wells and effect on production performance, JPT, 1990, pp. 1426-1433.

9. Suprunowicz R., Butler R., Vertical confined water drive to horizonsl well-

Part1: water and oil of equal densities, Journal of Canadian Petroleum Technology,

1992, no. 3, pp. 39-47.

10. Khasanov M.M. , Ushmaev O.S., Samolovov D.A. et. al. A Method To Determine Optimum Well Spacing for Oil Rims Gas-Oil Zones. SPE 166898. – 2013.