Introduction

When Oil & Gas production facilities come off plateau, many operators only then start to consider life extension programs to maximise the projected economic life of the asset. But, by adopting an early multi-discipline, integrated approach to key production areas, namely subsurface, wells, subsea (if appropriate), facilities and export routes, operators can better deliver cost effective life-of-field extension.

Recognising that Production Chemistry adds full industry value not only in the context of reservoir to refinery, but also in that of cradle to grave asset life, it has a strategic role in delivering life-of-field value beyond the original economic assessment. Key examples being;

  • Fit-for-purpose chemical programs for life-of-field (and beyond), flow assurance, scale control and particular focus on maintaining polymer integrity if required.
  • Assuring robust separation and produced water treatment that effectively mitigates the deleterious consequences of ever increasing produced water, polymer, solids and microbial issues.
  • Integration with Operations and Maintenance on critical Production Chemistry owned infrastructure, e.g. chemical/polymer injection, process filtration & mixing and resilience of injection and production systems.

Enhanced Oil Recovery (EOR)

EOR is the generic term for processes that further increase oil production from those reservoirs with significant additional Estimated Ultimate Recovery (EUR) potential. Compared to primary and secondary recovery levels of 20% to 40%, successful EOR programs have achieved recovery factors of up to 60%.

EOR requires early consideration for late-life application as it has a long validation process (often with both technical and commercial project gates) with specialist Production Chemistry work needed before final investment decision is made and full-field implementation initiated.

The following are examples of EOR techniques. As with all upstream projects, the choice of technique is field specific with multiple variables to consider.

Water Alternating Gas (WAG) CO2 Injection

Providing sufficient CO2 is available for injection, miscible water alternating gas (WAG) injection is an effective EOR method, as alternating injection of CO2 and water reduces overall gas consumption whilst also providing the enhanced displacement and pressure-support benefits afforded by the water. Though there is an enhanced subsurface scaling risk in carbonate reservoirs, the use of CO2 for EOR schemes has been extensively commercialised by US operators as Carbon Capture Utilisation and Storage (CCUS) programs, in some cases since the early 70s and 80s and continues to be a major focus for field life extension today.

Water Alternating Gas (WAG) Injection

This technique works in the same way as miscible CO2 WAG, but instead uses hydrocarbon gas and is often a solution for areas with stranded gas where there is no export route. However, miscibility is often more difficult to achieve when compared to CO2 and is susceptible to equipment (compressor) reliability and, even today, poor understanding of the development of the WAG bank through the reservoir.

Steamflood

As the name implies, steam is injected into oil-bearing reservoirs to heat heavy immobile crude, reducing viscosity and allowing extraction through production wells.

The two main steam processes are “soak” and “drive”. “Soak” involves intermittent steam injection into the near wellbore reservoir of a producing well, then letting the crude drain from the same well, whereas “Drive” works from a pattern of injector wells to build a reservoir steam chest that heats and drives newly mobile oil to producer wells.

Figure 1Modern Steam Injection Oil Pump Jack

Chemical/Polymer

Chemical EOR (cEOR) is a technology that has been adopted for many years where the goal of improving reservoir sweep efficiency is achieved by adding a viscosifying additive (or polymer) to increase the viscosity of injected water. This in turn reduces the tendency of water to override or finger through oil.

With a growing track record of research and program development, cEOR is seen increasingly as a viable option for both on- and offshore operations with a focus on improving production efficiency and reducing operating costs. There are however a number of Production Chemistry challenges associated with its application, including;

  • Supply & Handling – Delivery and make down of up to 200MT/d of dry polymer
  • Chemical/Mechanical Degradation – Interactions that reduces the viscosity of the polymer solution
  • Back Produced Polymer – Significant impact on separation and produced water facilities

Improved Oil Recovery (IOR)

This is an extension/subset of cEOR as it utilises, for the majority, polymer material to increase the hydrocarbon fraction of produced fluids. Techniques are often implemented as one-off or irregular batch treatments and are best described by the location of their application.

Water Shut-Off (WSO) and Relative Permeability (RelPerm) modification are the two polymer treatments often deployed in discrete near wellbore locations in production wells, whereas Conformance Control is like traditional cEOR in that it is applied through injection wells to help restore permeability homogeneity to achieve a better injection water sweep of the reservoir.

Production Chemistry Value

For most aspects of oil & gas operations that have a focus on asset life extension, including reservoir management with cEOR, downhole scale management or assuring subsea and facility performance and resilience, Production Chemistry plays a pivotal role.

There are many examples of how Production Chemistry contributes to the delivery of remaining asset value. The following two case studies are offered to exemplify the size and complexity of the contribution.

Case Study 1

Figure 2Middle East Steamflood

On a Middle East steamflood EOR, application of innovative chemistry/technology unlocked enhanced production on a large scale pilot program. Applied across the full field, each 1% increase equates to approx. 100MM barrels in additional reserves.

Case Study 2

Figure 3 – cEOR FullField Application

On a cEOR full-field application, Production Chemistry led process improvements on polymer make down plant, downhole application and crude/produced water production facilities delivered a future life-of-field savings estimated at $180-225MM.


James Johnstone

Principal Consultant - Production Chemistry