Controlling excess water production in fractured carbonate reservoirs: chemical zonal protection design

Bisweswar Ghosh,Hadi Belhaj,Samhar Adi Ali

doi:10.1007/s13202-020-00842-3

Abstract

Fractured carbonate reservoirs are prone to premature water cut production at the early stage of recovery. Conventionally completed long horizontal wells, suffering from high water cut through fracture networks, need reliable and cost-effective treatment solutions to control water entry, without damaging oil-saturated segments. Protection of oil flow channels from polymer gel invasion could be a challenge in complex fractured reservoirs because of the enormity of the number of zones that may require damage protection. In this work, a chemical package system is developed, comprising three different chemical solutions. The first fluid is designed to protect the low-permeable oil-saturated zones by creating an impermeable barrier while keeping the water conductive fractures open, followed by a gelant, designed to invade, solidify, and seal off the water conductive fractures. The third treatment is designed for a complete dissolution of the protective barrier created by the first fluid. The effectiveness of this process is evaluated through a set of four core flood studies at reservoir conditions. It was observed that whereas the effective brine permeability could be reduced by 74–91%, oil effective permeability is reduced by 12–17% depending on the fracture aperture. The paper also discusses the key parameters to be addressed for successful field implementation of this technology.

Highlights

High water cut oil production is an economic setback for the operating company, and with the advent of long horizontal extended reach drillings (ERD), controlling high water cut is becoming an even greater challenge
In view of the limitations of gelant-based water shutoff methods described above and the enormous opportunities exist due to the number of problematic horizontal wells throughout the world, we developed a novel water control system with the following objectives
It can be noticed that whereas matrix permeability of these core plugs was in the range of 40–50 mD, the fracture permeabilities were ranging from 1 to several thousands of Darcies representing a naturally fractured formation

Summary

Introduction

High water cut oil production is an economic setback for the operating company, and with the advent of long horizontal extended reach drillings (ERD), controlling high water cut is becoming an even greater challenge. Maersk Oil is the undisputable leader in drilling ERD wells with an average length of reservoir section reaching beyond 15,000 ft (Rushmore Reviews 2017). These wells are generally completed with casing/pre-drilled liners with downhole flow controllers and sensors to mitigate permeability heterogeneity and. Their observation differs from that of Reda is that, whereas Reda (2016) claims that oil reservoir aquifer strength has a little effect on produced water cut, Fang et al (2017) found great impact of aquifer size and strength on gas productivity and water cut, possibly because of higher dissolved gas in water

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Conclusion