https://orcid.org/0000-0002-8421-6751
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ABSTRACT
Accurate calculation of the moving range of oil-gas contact is important for the high-efficient development of oil-rim reservoir with condensate gas cap. The aim of this work is to establish an integrated analytical model for moving distance of oil-gas contact in the concurrent production of condensate gas cap and oil rim. Comparisons have been made between the new model, pressure gradient calculation method, and numerical simulation method (E300 simulator of Eclipse software from Schlumberger corporation) for a specific reservoir with only oil rim developed first. And the similarity was observed, which verifies the correctness of the new model. Then, the effect of gas recovery rate of the condensate gas cap, oil recovery rate, and injection–production ratio of the oil rim on the distance of oil-gas contact movement were analyzed. The results showed that, as the reservoir pressure decreased, the downward distance of oil-gas contact movement increased first and then decreased. The larger the gas recovery rate of condensate gas cap, the smaller the distance of oil-gas contact movement; the lower the oil recovery rate of oil rim, the lower the distance of oil-gas contact movement; the higher the injection–production ratio, the lower the distance of oil-gas contact movement. Moreover, the influential factors above were optimized to maintain oil-gas contact. When the injection–production ratio is 1.0 and the oil recovery rate is 1.5%, only the gas recovery rate of 3.5% can stabilize the oil-gas contact. The optimal gas recovery rate increases with the oil recovery rate and decreases as the injection–production ratio grows up.
Nomenclatures
| a1 | = | The radius of long axis of outer oil-gas contact under current condition, m |
| a1i | = | The radius of long axis of outer oil-gas contact under initial condition, m |
| a2 | = | The radius of long axis of inner oil-gas contact under current condition, m |
| a2i | = | The radius of long axis of inner oil-gas contact under initial condition, m |
| b1 | = | The radius of short axis of outer oil-gas contact under current condition, m |
| b1i | = | The radius of short axis of outer oil-gas contact under initial condition, m |
| b2 | = | The radius of short axis of inner oil-gas contact under current condition, m |
| b2i | = | The radius of short axis of inner oil-gas contact under initial condition, m |
| Bg | = | The current volume factor of condensate gas, m3/m3 |
| Bgi | = | The initial volume factor of condensate gas, m3/m3 |
| Bo | = | The current volume factor of oil-rim oil, m3/m3 |
| Boi | = | The initial volume factor of oil-rim oil, m3/m3 |
| Bw | = | The current water volume factor, m3/m3 |
| = | The average rock compressibility coefficient, 1/MPa | |
| cfp | = | The pore compressibility coefficient, 1/MPa |
| Gr | = | The initial gas-cap geologic reserve, m3 |
| Gpe | = | The cumulative hydrocarbon production from gas cap, m3 |
| h1i | = | The distance between the apex of top surface of condensate gas cap and oil-gas contact under initial condition, m |
| h2i | = | The distance between the apex of bottom surface of condensate gas cap and oil-gas contact under initial condition, m |
| N | = | The initial geological reserve of oil-rim oil, m3 |
| Np | = | The cumulative oil production of oil rim, m3 |
| p | = | The current reservoir pressure, MPa |
| pi | = | The initial reservoir pressure, MPa |
| psc | = | The standard pressure, MPa |
| Rp | = | The production gas–oil ratio, m3/m3 |
| Rs | = | The current dissolved gas–oil ratio of oil rim m3/m3 |
| Rsi | = | The initial dissolved gas–oil ratio of oil rim m3/m3 |
| Sco | = | The current saturation of condensate oil, fraction |
| SGwc | = | The saturation of connate water of gas cap, fraction |
| SOwc | = | The saturation of connate water of oil rim, fraction |
| T | = | The reservoir temperature, °C |
| Tsc | = | The standard temperature, °C |
| Vgas | = | The current gas-cap pore volume, m3 |
| = | The initial gas-cap pore volume, m3 | |
| Voil | = | The current pore volume of oil rim, m3 |
| = | The initial pore volume of oil rim, m3 | |
| We | = | The current cumulative water intrusion, m3 |
| Wi | = | The cumulative water injection in oil rim, m3 |
| Wp | = | The cumulative water production, m3 |
| = | The current water-vapor content of condensate gas, dimensionless | |
| = | The initial water-vapor content of condensate gas, dimensionless | |
| Z | = | The current Z-factor of condensate gas, dimensionless |
| Zsc | = | The standard Z-factor of condensate gas, dimensionless |
| Δh | = | The distance of oil-gas contact movement in the vertical direction, m |
| ΔSgs | = | The gas saturation of dissolves gas invaded from oil rim, fraction |
| ΔSw | = | The water saturation increment due to external water influx, fraction |
| ΔVf | = | The rock expansion volume for both gas cap and oil rim, m3 |
| ΔVfG | = | The rock expansion volume of gas cap, m3 |
| ΔVgas | = | The increment of gas-cap pore volume, m3 |
| Greek letters | = | |
| α1a | = | The formation dip of top surface of condensate gas cap in the direction of long axis, degree |
| α1b | = | The formation dip of top surface of condensate gas cap in the direction of short axis, degree |
| α2a | = | The formation dip of bottom surface of condensate gas cap in the direction of long axis, degree |
| α2b | = | The formation dip of bottom surface of condensate gas cap in the direction of short axis, degree |
| ϕ | = | The current porosity of condensate gas cap, fraction |
| ϕi | = | The initial porosity of condensate gas cap, fraction |