Engineering Design Challenges and Opportunities beyond Waterflooding in Offshore Reservoirs
Authors: Alvarado Vladimir , Manrique Eduardo J 
Published: May 2013

This paper presents an analysis on the potential of Enhanced-Oil Recovery (EOR) and its challenges in offshore environments. EOR experience gained in onshore and shallow offshore should be translatable to offshore, but common sense developed over years of exhaustive laboratory research, modeling based on our best understanding of recovery mechanisms and extensive onshore field experience must be redeveloped to adapt to the stringent demands of the offshore. We show how screening criteria and workflows recently developed can be adapted for evaluation of EOR potential in offshore environments. A quick review of some of the new vibrant offshore basins is presented.

Offshore EOR decision-making and design require integrated operations that merge more tightly traditional IOR, for efficient flooding, and EOR, to increase overall recovery factor. Screening criteria can be integrated through more adequate consideration of soft issues. The starting point of the needed mindset is the understanding of soft issues that harden to become barriers in the offshore. Large well spacing, limited space and its cost and unmanned operations are apparent constraints. However, more subtle aspects drive the EOR designer's mindset. The primary injectant in the offshore is seawater and its main derived challenge its proper disposal or reutilization after breakthrough. Close-cycle operations impose further understanding of the consequences of EOR downstream.

We show that opportunities abound, but disruptive technologies must be evaluated to overcome issues of reservoir characterization, but we also need deeper understanding of geochemistry and rock-fluid interactions as enablers of close-loop production. Production acceleration as a vehicle for upfront investment mitigation demands more-than-usual IOR through conformance. A number of examples of successful strategies offshore show that some of the challenges can be overcome.

The results of this analysis should serve to rank opportunities in a number of basins. The current market provides opportunities, but a more rigorous analysis of opportunities is required for their evaluation.

Introduction

Oil and gas production in offshore basins introduced new challenges to our industry. This translated into new paradigms such as unmmaned subsea wells. Shallow offshore operations were developed through anchored platforms, but as water depth increased, and cost and risk mitigation became even more important drivers for decision-making in these provinces, floating production storage and offloading (FPSO) units popularized.

Regardless of reservoir/field location, oil and gas recovery, including enhanced-oil recovery (EOR), operate under the same physical principles (Lake, 1996; Alvarado and Manrique, 2010a). This includes for instance miscibility conditions and reduction in water-oil interfacial tension, as in miscible gas injection and chemical enhanced-oil recovery with surfactants, respectively. However, without further considerations of well spacing, injectant delivery and downstream fluid processing as well as health, safety end environment (HSE), EOR decision making would be fundamentally flawed. This is the reason why EOR decision-making frameworks (Manrique et al., 2009; Alvarado and Manrique, 2010b) must be conditioned to adequately evaluate EOR opportunities offshore. Figure 1 shows a cartoon illustrating dire differences between onshore and offshore EOR operations. Some of these contrasting conditions impact the execution of offshore EOR pilot projects, in contrast with the more frequently attempted projects onshore.