Abstract
The aim of this study is to understand the effect of choke management strategies on the productivity of a Multi-Frac Horizontal Wells (MFHW) completed in a liquid-rich (gas-condensate) unconventional reservoir. The focus is the investigation of the how controlling drawdown during depletion impacts the formation, extent and structure of a condensate bank near the multiple fracture faces and how controlling bank formation through controlling drawdown influence productivity. Analysis of these productivity impacts was used to evaluate the most effective choke management practices in ultra-low permeability gas condensate reservoirs. Several fine grid compositional simulation models for MFHW completed in ultra-low permeability gas condensate reservoirs were developed. Parametric simulation studies were then performed using fluids with varying descriptions (e.g. dew point, initial CGR), varying reservoir properties (e.g. reservoir pressure, reservoir permeability) and varying well completion characteristics (e.g. fracture conductivity, distance between fractures). Condensate bank development was monitored in these simulations for various choke management scenarios. The effectiveness of each choke management scenario was evaluated and the best approaches were identified. There exists a misconception that for gas condensate produced from unconventional reservoirs, there is no benefit in managing drawdowns through choke adjustments. This misconception rises from the idea that in an unconventional gas condensate reservoir, large drawdown is required to produce the gas, and as a result, the pressure must fall below the dewpoint nearby wellbore and a degradation in performance due to condensate banking cannot be avoided. The results of our study show that, in some situations, the liquid recovery and cash flow per well can be maximized through choke management resulting in controlling the size and form of the condensate bank created. The main determining parameters is initial reservoir headroom (pi − pdew) and drawdown (pdew- pwf). If the head room is high, or intermediate, there is value in choke management, i.e. controlling (pdew- pwf), for both maximizing liquid recovery and also cash flow. However, if head room is essentially zero, then it is better to open the choke fully, i.e. maximize (pdew- pwf), from the beginning. In this last case, there is still a small incremental benefit in choke management if maximizing oil recovery is the primary value driver. This study shows that we can produce at BHP below dewpoint and still have CGR (t) remain a large fraction of initial CGR for significant producing times. The trick is to produce the well at condition close to succession of steady state. In this case, the size of the condensate bank remains compact, controlled and often relatively small over the production time of interest. This condition can continue until end of fracture linear flow regimes and beginning of Pseudo boundary dominated flow regime when the whole SRV goes to depletion mode. Note these results show that standard PVT descriptions can produce CGR(t) close to initial CGR for long periods during production and imply that dewppont suppression due to confinement in small pore spaces is not always required to achieve this.
