An innovative and sustainable portland cement-free alternative for oil and gas well cementing
Need to decarbonize well construction:
As decarbonization initiatives have emerged from all parts of our societies, the well construction process is not only aiming at producing oil and gas reserves, but also at the creation of carbon capture and storage (CCS), geothermal and water wells. Well construction will remain a planetwide activity for the decades to come, and it includes hard-to-abate emissions from well-cementing operations.
Reducing carbon emissions from cement is a priority in the oil and gas E&P sector because cement is used in nearly every well drilled today. Every ton of cement used creates approximately a ton of carbon emissions. Another reason for urgency is that our infrastructure has a long lifespan—on average 20–30 years—and the carbon footprint of wells and other E&P structures can last for decades. It is essential to ensure that future infrastructure is low carbon and does not lock in emissions for extended periods.
Cement manufacturing accounts for a bit more than 5% of the global anthropogenic CO2 emissions. From the global yearly operations, there is therefore more than 5 million metric tons of CO2 equivalent emissions that could be avoided during the well construction by embracing the challenging undertaking of well cementing without cement.
Developing geopolymer cement-free system for field scalability:
Geopolymer is considered a sustainable alternative to portland cement since it can be made from aluminosilicate sources found from industrial waste materials known as fly ash or slag. The material can also be generated from other naturally occurring raw material sources that, in the future, will expand the availability or raw materials. It is described as an amorphous, three-dimensional inorganic polymer formed by chemical dissolution of the raw materials in a high pH alkaline solution and subsequent polymerization of aluminosilicate in an alkaline solution, as shown in Fig. 1. The set product is chemically more stable compared with portland-based cements.
Geopolymers, already well known in traditional construction industries, show promise as alternatives to portland cement for use in oilfield wells. However, in the past, the industry did not have enough knowledge of the chemistries and experience in terms of designing for downhole conditions. Unlike portland cement, which the industry has been using for over 100 years with well-established chemistries suitable for downhole conditions of enhanced temperature and pressure, successfully moving geopolymers from a concept in the laboratory to execution at the wellsite remained a massive challenge. Settings for surface conditions that are required for the normal construction industry are easier to achieve with geopolymers. However, for an actual well construction environment, there is a need to develop appropriate chemistries that will work at elevated pressure and temperature downhole.
SLB has spent many years in extensive research and development to evolve a new portfolio of products that can support the use of geopolymers under downhole conditions of temperature and pressure. The portfolio includes liquid additives for offshore operations and a robust solid package for land locations that will allow for all additives to be added in the blend and for operations to be performed with ease at the rig site by just adding water. This approach significantly simplifies the logistics and execution, especially for land operations, and it minimizes the health safety and environmental (HSE) footprint for the job. The use of raw materials from local sources minimizes the transportation associated environmental footprint
The evaluation of geopolymer application for oil and gas well construction was divided into the following main phases: development of robust chemistries and slurry designs in the laboratory with testing protocols using standard lab equipment and API procedures; ability to model the primary cementing job using geopolymers with CEMENTICS™ zonal isolation software; confirmation of the fluid compatibility with oilfield equipment for field application and scalability for safe execution in the field; and validation through conventional postjob evaluation techniques used in the industry.
The laboratory work included an engineered, innovative approach to chemistry to obtain a slurry matching and exceeding performance of portland cement-based designs for placements. The project considered new chemistries that would enable design of the required properties for a liquid slurry like thickening time, fluid loss, and rheology and then provide the right performance in terms of compressive strength, low permeability and long-term durability when set hard. Yard trials verified compatibility of geopolymers with industry-standard oilfield cementing equipment and ensured that the properties of the slurry mixed in the field were like the initial design. This was conducted in multiple locations using local raw materials by mixing and batch mixing the slurry. This ensured that the slurry was flexible enough to be mixed and pumped using any of the processes conventionally used in the field. The blended products were transported in the mobile bulk silos to ensure the stability of the blends during transportation to the rig site and from one silo to the next. One of the challenges in the field operations is related to difficulty in getting the blends out of the silos. To test this, SLB has specially developed protocols including powder rheometers and tests on aeration energy. Robustness, flowability of blend was confirmed first in the lab and then by performing blending of realistic quantities of blends that would be required for actual jobs in the bulk plant. The geopolymer-based designs were then scaled up to meet typical cementing job volumes and executed at the wellsite for different casing configurations and downhole conditions without deviating from conventional operating procedures. Postjob evaluation techniques to validate the placement included pressure matching and cement bond logs.
The jobs were all modeled through zonal isolation software and postjob pressure matching (Fig. 2) was performed using the same. The pressure matched very well between what was simulated by the software and what was actually seen on the job. This confirmed that the software used could be extended to the newly developed systems. Multiple wells were logged using the conventional sonic and ultrasonic tools that confirmed suitability for measuring presence of set geopolymer behind the casing and providing a better bond log response when compared with portland cements. The set solid material was clearly visible behind the casing. One of the intrinsic properties in the geopolymer materials is that it does not shrink, unlike the portland-based cement systems that may give 1 to 2% bulk shrinkage typically. Shrinkage leads to debonding of the casing from cement and impacts the bond log response. Hence, geopolymers provide a better bond log response. The system has been commercialized as EcoShield™ geopolymer cement-free system.
The geopolymer cement-free system has shown excellent mechanical strength, thermal stability and chemical resistance, which makes it useful for various applications in construction and the drilling industry.
The geopolymer cement-free system can be deployed throughout various phases of the well life cycle including abandonment. It can also be deployed across a range of field applications, including corrosive environments while delivering superior technical performance. To date, the technology has been used in over 50 primary cementing jobs, within intermediate and production strings of various profiles including long horizontal laterals.
Bringing performance sustainably:
Every ton of cement manufactured results in approximately a ton of CO2 equivalent emissions. In addition to its embodied CO2 emissions, portland cement creates significant transportation-related emissions from manufacture to deployment sites, especially in locations where API portland cement that is qualified for the oil and gas industry is not available and has to be bought in from other countries and continents.
An important step in decarbonization is using an end-to-end approach to quantify carbon emissions during cementing operations. By careful analysis of the entire cementing operations process, it is then possible to measure and compare carbon emissions at various stages of the operation. Understanding and isolating the main drivers of the carbon emissions footprint enables making better choices and developing best alternatives with lower environmental impact.
The methodology considers the lifecycle assessment of cement from quarry extraction to well abandonment and includes steps such as manufacturing of raw materials, transportation and logistics and operations in the field. For these stages, careful quantification of emissions is performed based on the manufacturer’s carbon emissions of cementing products, transportation (distance and means) to the bulk plant and rig site, and equipment-related emissions such as blending and pumping units. In some cases, when assessing the footprint of different technologies, a sensitivity analysis can be carried out to compare the operation-related emissions based on a field case.
Using an assessment tool during key cementing operations allows for identifying the main contributors to greenhouse gas (GHG) emissions. In most cases, the embodied carbon in the cement slurry itself outweighs the operational emissions (on an average, one ton of CO2e is emitted for every ton of portland cement produced). The embodied carbon of cement systems mainly depends on the data quality of the emission factors of the slurry components. These factors are not yet broadly available, and until then, correct proxies are needed to perform such studies.
Besides the embodied carbon, the assessment tool also quantifies other elements of the cementing operations. Examples of sensitivity analysis will be presented, covering aspects such as an optimal transportation choice from the supplier location to the implementation site. Furthermore, the tool supports the selection of cementing technologies, integrating performance and larger impacts such as a change in the well design or elimination of remedial operations during the life of a well.
The cementing emissions planner supplies a platform for consistent and transparent quantification and comparison of cementing technologies supporting an effective environment action. This tool embraces forward-thinking and innovative cementing solutions that help decarbonization in the oil and gas industry in achieving net-zero carbon emissions.
The geopolymer cement-free system uses locally sourced natural materials and industrial waste streams in its composition, making this a far more sustainable technology. The system as a low carbon alternative eliminates up to 85 percent of embodied CO2 emissions compared with conventional cement systems, thus enabling the benefits of a circular economy.
Conclusions
- An engineered one-sack geopolymer system was developed to meet the requirements of cementing operations and offers several benefits:
- 1-Safe operation by elimination of corrosive liquids handling
- 2-Compatibility with existing cementing equipment
- 3-Operational efficiency through removing the step of preparing the mix fluid
- 4-Ability to mix the slurry onsite by adding water to the preblend.
- The performance of the developed geopolymer was verified in the laboratory against portland cement and validated by execution of a yard test. The success of the conducted yard trial confirms the readiness of the geopolymer technology for large-scale deployment in oilfield as it has been shown to provide the necessary properties for well integrity and is safe and reliable in operation.
- Introduction of the geopolymer cement-free system requires the adaptation of innovative chemistry into the slurry design, however, it can be successfully implemented using the existing infrastructure that has evolved from the historic use of portland cement. Results including standard sonic and ultrasonic cement bond logs have shown that for primary cementing applications, the geopolymer cement-free system is an effective alternative to portland cements.
- It’s a true collaborative project bringing together by-product owner and disposal companies, upstream technology and operating companies, regulatory bodies and various associations that set the industry standards for the decades to come.
Decarbonizing the well construction process while ensuring safety and performance standards is critical to our industry’s pathway to net zero. EcoShield geopolymer cement-free system is a breakthrough that delivers industry-standard zonal isolation capabilities while significantly minimizing impact from upstream oil and gas production.
The geopolymer cement-free system is an example of accelerating decarbonization through innovation and science. The system is part of the SLB Transition Technologies™ portfolio, which includes proven technologies that drive high performance while reducing CO2 emissions. These types of more sustainable, lower-carbon technologies are critically important today as we continue to discover and develop the new energy solutions of tomorrow.
