Gas injection is the process of injecting natural gas (miscible and immiscible) or nitrogen (immiscible) to the reservoir, to push the oil to a producing well. The purpose of immiscible natural gas (dry gas) and nitrogen injection is to maintain pressure in the reservoir and create a gas cap. Sometimes nitrogen is used to capture oil that was trapped, as well. Miscible natural gas (lean gas, LPG or rich gases), on the other hand, is used due to its ability to mix with oil, also known as miscible with oil.
Why it is required? Oil and water cannot be mixed into a homogeneous liquid, which in turn makes it less effective when water is used to push the oil. However, if the injected gas is miscible with oil, it will become a homogenous mixture, that will expand and allow the forces of injected lean gas to be used effectively, moving oil more easily towards the well. This method needs a high reservoir pressure in order to work effectively, as well as sources of economically cheap gas, normally lean gases (residual gas -methane and ethane).
It is important to make a distinction between gas injection and gas lift, as these are two different processes. In gas injection, as part of EOR, gas is injected through separate injector wells that are usually spread across the field in a predetermined manner. Gas lift, on the other hand, is an artificial lift method, whereby a pressurized gas, produced by a nearby well, is injected continuously or intermittently into the production tubing to lift the fluids. Injected gas travels to the reservoir through a gas lift valve at a certain depth. The underlying principle of the gas lift method is that gas reduces the density of the fluid by aerating it with gas bubbles. This, in turn, reduces bottom-hole pressure, aiding fluids from the reservoir to travel to the wellbore faster and easier.
While onshore logistics makes it easier to conduct a gas injection Enhanced Oil Recovery (EOR) project, in the offshore environment it is a lot more complex, challenging and costly, due to the fact that existing infrastructure was not designed to accommodate it, in terms of weight, space, handling capacity and power. Depending on the size of the project, a specialized platform might be required to conduct offshore gas injection EOR projects. There are a number of constraints that should be considered and planned in advance, such as tanks and storage capacity, manning capacity to accommodate the required crew, pumping and supply capacity. In general, best practices and facilities for onshore gas injection EOR may not apply offshore.
Feeding gas is a huge challenge that may be too costly to overcome, due to high H2S content in the natural gas available in the region.
Enhanced Oil Recovery (EOR) is a set of activities and techniques designed to reduce oil saturation and increase the oil recovery rate. In general, oil production is divided into 3 stages: primary, secondary and tertiary (improved). The tertiary method is also called as Enhanced Oil Recovery (EOR).
EOR is used when the primary (natural flow) and secondary (water and gas injection) methods are no longer effective and normally leave around 60-80% of oil unrecovered. Using EOR can help to recover more oil, and help to achieve higher recovery rates. For gas wells, the primary production method is normally enough to produce around 80% of the reserves. Hence, EOR is used in crude oil production.
EOR techniques are very costly and the price of oil is a key factor for an operator when decisions are made on what EOR technique to implement. What could be technically feasible might be expensive and not economical? In addition, there is always a dilemma between exploration (to find more oil) and EOR, and sometimes exploration risks are too high, thus companies choose EOR approach instead. In addition, the pace of new oil discoveries and its size has been declining; hence producing more oil from existing fields is dominant thinking for a few years to come.
Screening criteria on of which EOR method to deploy require a detailed analysis of a particular field and its location, reasons of lower recovery rate following primary and secondary methods, is conducted to understand the strategy and what EOR approach to apply. Due to a number of reasons, both technical and commercial, EOR makes economic sense in larger fields.
Offshore EOR makes it even more challenging and costly, due to the fact that existing infrastructure was not designed to accommodate equipment packages associated with it in terms of weight, space, treatment facilities and power generation. In addition, due to well-placement offshore and the distance between the wells, any EOR campaign will require more time to have a noticeable effect. On average an EOR project takes 1-7 years till it is fully deployed. Laboratory testing and pilot projects are prerequisites of any full-scale EOR development and can take up to 4 years to complete.
EOR is divided into 4 distinctive categories as shown below.
Each EOR technique has its own use in and it is hard to be definitive with any particular EOR technique, as every method unique enough to work better in some cases than the others. Below are a guide and major characteristics of available EOR methods.
Worldwide, EOR contributes to less than 2% of global crude production. CO2- EOR is the largest and most widely used EOR method, followed by Thermal injection and Gas Injection.
After long years of production, the recovery rate in most of the fields in the GCC is coming to a point, whereby focusing on EOR considerations become more and more important - most oil fields in the region have been under primary and secondary production for decades. Although the fields do not require any EOR yet, some of the EOR projects in the GCC are one of the world's biggest and challenging, whereby the most advanced technology is used. Those include steam injection and polymer flooding in Oman, gas injection in UAE and CO2 pilot projects in UAE, Saudi Arabia, and Qatar, with more steam injection projects on the way in Kuwait. Oman is the regional leader in EOR projects and has implemented thermal, chemical and gas injections projects. It is estimated that by 2020, EOR production in Oman will be around 22% (PDO).
As a result of growing population and efforts to maintain and increase oil production in the GCC, it is becoming more challenging to meet the demand for natural gas to cater to power generation, gas re-injection projects and steam generation. Hence, focus on other EOR methods, such as chemical and CO2, will be evident in the years to come.
CO2 EOR projects are gaining more traction, not only because of its favorable economics but also as part of sustainable practices, as well as preserving natural gas used for gas injection, for power generation purposes and alike. There have been a number of research centers established in UAE, Qatar and Saudi Arabia to make progress in applying CO2 EOR in the region. NOCs in the region are taking proactive steps to establish a knowledge base and expertise ahead of time.
EOR is challenging and time-consuming and ineffective screening may result in lower-than-expected recovery rates. It is a common practice to conduct small trial projects to understand which EOR technique delivers the best project economics. In addition, the environmental impact and effects of chemicals could be best understood in smaller projects.
Some of the giant fields in GCC will not require EOR for the next 20-30 years. However, certain fields may need one in the next 3-5 years. The chart below represents the projected growth in EOR production worldwide. Growth in EOR production in GCC is evident and represents a notable proportion of GCC oil production.
Supply & Demand Dynamics
Supply & Demand Dynamics
Global demand for gas injection EOR services will continue to be the second preferred method, after the thermal recovery option. However, with more emphasis on the environment and improved technology, the economics of CO2 EOR will result in higher utilization of this particular method and reduce the demand for gas injection EOR.
In the GCC, this change will be particularly evident due to power generation requirements. As a result of the growing population in the region and efforts to maintain and increase oil production, it is becoming more challenging to meet the demand for natural gas to cater to power generation, gas re-injection projects and steam generation. Hence, focus on other EOR methods, such as CO2, will be evident in the years to come and greatly affect any appetite for gas injection EOR projects.
Application of gas injection (miscible) projects in the GCC is limited to Harweel field in Oman and to a lesser extent in the Abu Al Bukhoosh field in UAE.
Cost & Price Analysis
Cost & Price Analysis
EOR production is considered as a project in itself and requires a large number of equipment and packages. Studies, pilot projects, engineering design, equipment procurement, feedstock planning, drilling, and other materials, play an important role in EOR projects. Upfront capital costs in EOR projects are significant.
Availability of gas, its opportunity cost and infrastructure re-development play one of the key roles in cost basis for any gas injection EOR.
Almost every EOR project is bespoke and requires a large number of studies, pilot projects, and simulation. As a result of this, equipment and packages are not standard and may require bespoke engineering and manufacturing every time, which in turn reduces the diversity of available suppliers, increases costs and lead times.
The most critical levers that would influence the costs and procurement decisions are
- A comprehensive FEED study
- Analysis of the supplier market and their capabilities.
While there are numerous engineering companies providing the services of FEED studies, companies who specialize in the EOR studies and consultancies are in a better position to produce a more valuable and meaningful FEED - as they have large exposure to varus EOR projects.