In their push to optimize field operations, oil and gas operators continually look for new ways to boost long-term production from their wells while keeping costs down and minimizing any impact to the environment. Infield power generation is one area that is garnering increased attention in this regard.

While diesel fuel has reliably powered oilfield equipment, natural gas-powered engines and generators are growing in acceptance as a viable and cost-effective alternative to diesel—particularly when a reliable supply of natural gas is available.

Among the benefits natural gas generator systems provide over conventional diesel systems is their economic advantage in the long term. While natural gas units carry larger upfront capital expenses, they have been shown to cost 40% to 45% less to operate than diesel units, primarily due to fuel savings. These units generally exhibit longer run times between service intervals compared to their diesel counterparts, thus maximizing field uptime. Natural gas units also use field-proven “lean burn” technology to meet emissions guidelines at both federal and state levels.

Much of the focus of natural gas-powered rental equipment has been on drilling and hydraulic fracturing operations. However, there is growing interest in expanding this power option for the production phase of an asset. Artificial lift systems that use electrical motors, for example, are a long-term production application that can benefit from natural gas power.

Addressing deployment challenges

For operators to take full advantage of the benefits of natural gas power generation in the field, they must first be aware of the challenges in deploying this option on a large scale. They must then develop a power supply strategy in partnership with a third-party supplier that is flexible and scalable to address these challenges and meet the needs of each stage of field development.

Temporary power solutions can address these deployment challenges as well as other challenges that are preventing widespread adoption of natural gas power generation, which currently include the following.

Being able to deploy an alternative fuel power plant as quickly and as large as a diesel plant. Ensuring efficient and seamless installation of alternative fuel power is addressed by partnering with a temporary power provider capable of supplying all components in an integrated package. Such a package includes modules to condition the field gas by removing water and acid gases like hydrogen sulfide (H2S), electrical infrastructure including the generators and cabling to connect to the drilling rig or artificial lift system, and accommodations to hook up an alternative fuel source such as liquid propane or LNG in the event that the main gas supply is disrupted.

Having the capability and knowledge to use field gas with varying Btu content. When handling varying Btu-content field gas, some upfront processing is usually required to remove higher Btu components (ethanes, propanes and butanes) and water from the methane. The power provider should have the in-house expertise and technology to reliably separate these components from the methane stream, allowing the operator to capture the higher Btu components rather than flare them off.

Being assured of consistent power generation in the face of changing gas supply volumes. Achieving consistent power generation when the gas supply varies is addressed by a system that is flexible with regards to fuel source. Gas from the wellhead or from the pipeline is often the most cost-effective and reliable source as it avoids the need to ship in fuel in the form of LNG or CNG. In fields that are forced to flare gas because they do not have adequate capacity or infrastructure in place to handle excess gas production, it makes sense to divert this gas for power generation. Not only does this option minimize field emissions, it also allows the operator to capitalize on a fuel source that would otherwise be lost.

In remote or rapidly developing field locations, dual-fuel options such as the use of liquid propane-powered engines are available. This option is particularly attractive in the early days of field production before a steady source of field gas is available. Production can initially be powered by liquid propane, which is eventually switched out for natural gas once the infrastructure is in place to reliably access gas from nearby pipelines.

Maintaining reliability and ensuring adequate real-time monitoring in the field. Reliability is addressed by monitoring various field parameters, including flow rates into the generator and electrical output to the rig or production equipment. This information is relayed in real time from remote field operations to a central office, providing operations personnel with constant access to the working condition of the generator. The system also includes alarm functionality to immediately notify personnel of a problem with gas supply or generator function in the field. A repair team can then be sent directly to that location to address the problem and get power generation running at its optimal output.

Realizing results

In a remote part of West Texas, an operator had limited access to electric grid power, which curtailed expansion plans and presented challenges in maintaining production from existing wells. As a result of limited grid electricity, more than 16 of the operator’s wells were underdeveloped or shut in.

The operator needed a temporary power solution, but fuel options including diesel, LPG, LNG and CNG were considered uneconomic. Field gas was readily available, although it was in the form of wet sour gas containing greater than 300 ppm of H2S. A permanent solution to cleaning this gas also was considered cost-prohibitive, and with a utility upgrade still six months away, the operator needed an alternative power solution for its immediate needs.

The operator consulted with a power supplier to develop a scalable and easily deployable temporary power management solution. Technical specialists worked with the operator’s field operations team to engineer a cost-efficient strategy to scrub the toxic sour gas out of the stranded field gas supply and turn it into a viable fuel source to power a temporary natural gas generation station. The temporary station was designed to work in parallel with the utility grid, providing the incremental power required to run gas-lift equipment and other production operations.

The temporary power solution was able to reduce the H2S levels in the supply gas to 0 ppm by passing through a tower equipped with SulfaBate pelletized H2S scavenger. The solution also included multiple gas-liquid separators to reduce the liquids content of the gas prior to introducing it to the generators and a temporary flare to purge test gas. The dry, desoured gas then entered two 1-MW natural gas generators, which provided parallel and base load with the utility grid at 12.4 kv.

This solution was able to power a fully operational well site less than one week after startup and generated a payback greater than 10:1. With the additional electricity supply afforded by the temporary power system, eight wells were able to convert from rod pump to electrical submersible pump as the lift method. This conversion increased the operational capacity of the field crew, which immediately began drilling new wells to continue toward the goal of 100% operation of available production.

Regardless of its size, any natural gas power generation system should address a number of issues in the field. First, the system must be capable of running efficiently on natural gas of varying Btu content and from different sources. The system should be able to deal with intermittent supplies of natural gas and automatically switch to another fuel option if necessary without causing any delays or interruptions in field production. And ultimately, the power system must run reliably for long periods with minimal requirements for maintenance or downtime.

Acknowledgment

This paper was presented at the SPE 2014 Artificial Lift Conference North America held in Houston Oct. 6-8, 2014.