Abstract

Gas-condensate reservoirs usually exhibit complex flow behavior due to the near-wellbore condensate bank build-up when bottomhole pressure drops below the dew point. Such an accumulation of condensate liquid in the near-wellbore region forms a ring that may significantly reduce the gas relative permeability and consequently the well productivity. Also, when reservoir pressure drops below the dew point, a big portion of condensate liquid will remain in the reservoir and will not be produced.

Many condensate reservoirs have been producing with vertical wells. This paper presents a practical strategy of rejuvenating gas-condensate reservoir production through multilateral sidetrack reentry drilling technology. Simulation studies show that reentry drilling through vertical wells can help break the condensate bank damage and significantly increase well productivity.

Sensitivity analysis of fluid type, reservoir permeability, lateral length, and reentry drilling time on production performance, is conducted. Results show that multilateral reentry drilling represents a very promising technology for developing medium/low permeability gas-condensate reservoirs.

Introduction

Gas-condensate fields have significant industry importance. The profitability of gas-condensate field development depends on both gas and condensate production profiles.

Two major reservoir engineering problems associated with gas-condensate reservoir development are:

  1. possible drastic drop in gas productivity when pressure drops below dew point pressure,

  2. loss of condensate trapped throughout the reservoir at the end of exploitation.

The loss of productivity in gas-condensate reservoirs due to near wellbore condensate dropout is well discussed in the literature.[1,2,3,4]

Reentering wells to gain additional production is not new. Since the mid-1950's, oil companies have reentered old wells and drilled sidetracks to bypass formation damage or wellbore mechanical problems, and to exploit new zones, saving the cost of drilling entirely new wells.[5,6]

In this study, we proposed a practical strategy for rejuvenating vertical well production of gas-condensate reservoirs under depletion through reentry drilling of multilateral branches from existing vertical wells to bypass the condensate bank zones.

Comprehensive simulation studies, using industry-standard reservoir simulator ECLIPSE© (trade mark of Schlumberger), were conducted to investigate the potential of this technology in different reservoirs. Sensitivity analysis was also done to evaluate the effect of fluid type, reservoir permeability, lateral length, and reentry drilling time on production performance. Results show that this technology will be very promising for application in medium/low permeability gas-condensate reservoirs.

For actual field implementation, a more detailed reservoir simulation study with proper geological description and project economic analysis should be conducted to guide the successful design and application of this technology.

Simulation Model and Parameters

A 3-D model of a hypothetic field is used in this study. The field is produced by natural depletion without considering any pressure maintenance.

The simulation model and parameters are described as follows.

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