By Reagan James, Hanne Størksen, ConocoPhillips Scandinavia AS
Products and substances providing a common health, environmental and technical functional excellence are only achieved today after challenge. The challenge includes innovative chemical engineering, comprehensive testing and field proving. This has come about owing to the increasing diversification of the three disciplines, and the dilemma is to attain a satisfactory result on all counts.
This article will share the experiences of ConocoPhillips Scandinavia regarding the selection and use of products and substances for operations and how the company gained industry-leading health, safety and environment (HSE) characteristics while maintaining operational technical requirements.
ConocoPhillips Scandinavia, earlier Phillips Petroleum Company Norway, has operated in license area PL 018 in the southern Norwegian North Sea sector for more than 40 years. The area, typically known as the Greater Ekofisk area, is relatively uniform in water depth, formation type and reservoir characteristics. This has provided an opportunity to try, compare and measure the consequences of many HSE improvement initiatives.
The uniformity also allowed the company to test many of the new and innovative drilling fluids systems of the early 1990s. The initiative was to address difficulties experienced with the water-based drilling fluid used at the time by identifying an acceptable alternative drilling fluid. Because monitoring of sea bed conditions was being conducted for discharge contamination impact in each three-year period, the Norwegian Pollution Control Authority (NPCA) allowed the company to use and discharge the new synthetic oil-based and cationic water-based drilling fluids systems.
Drilling platform locations in the Greater Ekofisk area were identified to try the fluids in places where cross-sea bed contamination would not occur. The sea bed studies indicated that the new drilling fluids systems degraded slower than laboratory studies showed. However the advantage of the new drilling fluids systems was significantly reduced drilling times for operations. The NPCA was provided information regarding the degradability characteristics of the alternative fluids.
Fundamental principles have ensured that the products and substances can be selected in a balanced manner. For example, an internal evaluation and control system, the Hazardous Substance Management System, requires the collaboration of technical, health, safety and environment personnel. The company also maintains an open relationship with the NPCA and the Norwegian Petroleum Directorate (now the Norwegian Petroleum Safety Authority), collaborates with research and analysis institutes, stimulates manufacturers towards improved products, and ensures regular meetings with suppliers for this purpose.
In 1993, ConocoPhillips Scandinavia recognised that a system was needed for appropriate substance and product selection and use, and for improved safety, work and marine environment conditions. A committee was formed to address the approval-for-use, inventory, control and documentation issues associated with substances, chemicals and products, generally known as “substances” in all work areas both offshore and onshore. The committee established the Hazardous Substance Management System, and its use continues today.
The system’s functions are:
- To document all substances in work areas, including all chemicals and products except medicines, foodstuffs and stationery materials such as paper, pens and marking inks. Welding rods and materials that change chemical form under use are included.
- The system controls substances purchased and used by using a blockage link between the HSE and purchasing data systems.
- The approval process for new substances has three elements: work environment, marine environment, and technical or operational requirements. This process ensures that the substances are reviewed and justified for their introduction and screened periodically as the Hazardous Substance Management System is refreshed.
- To inventory the quantities of substances. The inventory listing also specifies exact locations in all areas of the substances. This was achieved by creating coded area modules of all locations. A regular physical inventory check noted safe storage practices and correct labelling of the substances and products. The system also identifies products that are incorrectly located, e.g., in a zone unacceptable to the hazardous nature of the substance.
- To register and specify the substances in all respective areas. Information from this register is used primarily by the medics/nurses on a location or platform. The information allows them to be medically prepared in the event of an accident with a particular substance.
- It identifies similar product types that the company is purchasing from different suppliers.
When the system was implemented, it indicated that over 2,000 products, chemicals or substances existed in all Greater Ekofisk areas. This resulted in a campaign to reduce the number of substances. Within a 24-month period, the total number of substances was reduced to approximately 800 by selecting similar products or substances from one supplier rather than a number of suppliers. Today, the company operates with approximately 700 products or substances.
- To enable control checks to ensure that substance documentation is correct and acceptable, e.g., the Material Safety Data Sheets must meet the Norwegian standard.
- The Harmonised Offshore Chemical Notification Format, containing ecotoxicological documentation, must be approved for products and substances as required by Norwegian regulations of HSE activities.
- To comply with regulatory requirements.
Implementation of this system impacted all product and chemical suppliers. Suppliers who were able to meet the required standards were positively received; those not willing to readily comply with the correct Material Safety Data Sheet information, for example, received assistance towards completing satisfactory documents.
Establishing the Hazardous Substance Management System was instrumental in raising personal awareness of improved practices and to the required Norwegian premises of all employed in operations.
Some health, safety and environmental quantifying studies:
Technical challenges are constantly present as operations continually push the opportunity window. As the technical aspects are addressed with new or substituted substances, the HSE characteristics of each substance must also be evaluated carefully.
HSE screening processes have many forms. In some cases, the company modified screening procedures and methods in order to adequately determine the potential hazard of questionable substances. Here are a few examples of these screening processes and the results gained:
Selection of a mineral base oil for drilling operations
Mineral base oils that were typically used up until the mid-1990s contained up to 6% aromatic hydrocarbons. Owing to an increasing focus on occupational health in the early 1990s, a safer base oil fluid was needed both for work environment purposes and to maintain acceptable drilling operation conditions, not to mention be commercially viable. The company initiated a study in 1996 to identify such a base oil. The company specified the desired parameters and appointed a drilling fluids contractor to perform the study.
The identification and selection process took almost one year, and the successful base oil supplier and drilling fluids contractor cooperated to provide the base oil. The studies provided the industry with a base oil occupational hygiene “benchmark” value. This base oil, and comparable base oils, have since become more broadly used in the Norwegian sector for drilling purposes. An additional significant improvement resulting from these studies has been the identification and removal of the low n-C alkane values that are the most volatile.
Offshore drilling operations where mineral oil-based drilling fluids are used have been monitored closely. The company industrial hygienist ensures that work area air samples are routinely collected and analysed.
Headspace quantification of volatile substances
“Headspace” refers to the natural vapour emission of a liquid or solid substance. ConocoPhillips Scandinavia has been an industry leader in analysing base oils and products used in non-aqueous fluid systems, alternatively known as oil-based muds (OBMs). The results of these earlier studies have challenged the industry to improve base oil and product additive characteristics for reduced and controlled headspace values.
A reduction of the headspace value will result in lower vapours from the non-aqueous fluid system when used for drilling purposes. The control of the chemical components in the vapours emitted will also help provide a safer work environment.
Because there was no appropriate headspace testing procedure, the company developed one in conjunction with a base oil supplier. It was quality reviewed for its test regime competence by subject specialists within the company and analytical institutes. A summary of the test procedure reads as follows:
“The test procedure is to compare the compositions of the vapour phases of samples by taking a portion of the vapour from a sealed, heated vial and injecting it onto a gas chromotograph capillary column. A sample history can have a significant effect on the headspace it produces. Ideally any sample under test should be a recently manufactured and representative sample of the material and without any exposure to weathering.
A 1.0 ml sample of the material to be analysed is pipetted into a 20-ml headspace vial, which is capped with a crimp-on seal. The sample is thermostated at the test until equilibrium is reached. A sample of the equilibrium vapour phase above the liquid sample (the headspace) is then injected onto the gas chromotograph column.
The total Flame Ionisation Detector response of the sample headspace is compared to a vapour sample from a known mass of totally vaporised iso-octane, to determine the headspace concentration.”
Drilling fluid additives are not an openly defined chemical group. However, the major additives in a non-aqueous fluid system, such as emulsifiers, rheology builders and wetting agents, can be viewed as active chemicals dissolved or dispersed in suitable solvents. Gas chromatographic analysis has revealed these additives to be complex mixtures containing large proportions of highly volatile solvents.
Owing to ConocoPhillips Scandinavia’s ongoing headspace studies, the volatile solvents in the emulsifier and wetting agent additives have been substituted with products of significantly lower volatility, or headspace. This change has been cautiously accomplished without affecting the technical performance of the additive, but it has resulted in a higher product or additive cost per unit.
Individual drilling fluid additive headspace and reactions
The total headspace of the individual drilling fluid additives are also diverse (Table 2). Total vaporisation of small volumes – for example, 1 micro-liter – of the samples at the higher temperature of 155°C is necessary to calculate the parts-per-million equivalent per unit area for each respective sample.
Relative headspace values
Table 1 indicates that various base oils exhibit measurable differences in total headspace. For example, Base Oil B is typically twice that of Base Oil A. If improvements to occupational health are to be addressed, base oil choice is one crucial factor that must be considered.
The relative headspaces of the different drilling fluid additives, including base oils, are significant and diverse. Study results indicate that the headspace for each of the liquid additives is generally at least an order of magnitude larger than that of the base oils studied. A relationship is illustrated where Base Oil A has been given the arbitrary value of 1 (Table 1).
Case Histories Ilmenite
The use of ilmenite instead of barite as a weighting material provides a simple illustration of the product selection dilemma. Although the company was re-injecting all drilling waste streams in 2001, it used ilmenite instead of barite for all drilling operations because:
- The Norwegian Pollution Control Authority considers “use and discharge” as a criteria in their permits.
- Ilmenite is available in Norway from a mine near the company’s offshore supply base.
- Ilmenite has significantly less barium and heavy metals such as lead, copper, chromium, aluminium and zinc than barite.
- Ilmenite has a higher specific gravity than barite, meaning a reduced solids content in the drilling fluid and reduced logistics concerns.
The composition of ilmenite is approximately 50% iron oxide and 50% titanium oxide. The iron fraction is magnetic. Outwardly this would not appear problematic and, for many drilling operations, would not be a concern. But for the Greater Ekofisk area, where over 800 wells have been drilled within a 35-km by 12-km area, directional drilling operations of new wells must be precise.
Ilmenite’s magnetic characteristic had to be compensated for in the directional drilling tools and associated software. Additionally, while drilling a well, ilmenite concentration varies according to the desired density of the drilling fluid. This compromises, to a degree, the compensation in the directional tools. Two other compensatory measures needed in these tools cannot be avoided:
a) Adjustments according to the Earth’s natural magnetic field changes. These changes are monitored on a 24-hour a day basis to ensure optimum accuracy.
b) Adjustments depending on the sun’s activities, especially sun spots.
The additional interference of the iron oxide from the ilmenite was deemed avoidable, and the field use of the product was terminated. Incidentally, rig deck areas that had been exposed to drilling fluid containing ilmenite or ilmenite dust were significantly harder to clean to the point that extra cleaning personnel were required. This condition was also attributed to the magnetism of the ilmenite.
Oil-based drilling fluids
Oil-based drilling fluids combine a number of dilemma characteristics concerning the selection of an appropriate base oil, emulsifiers and rheology modifiers. The selection of any products in these groups is compromised with respect to local regulations and prudent practices. Norwegian regulations and drilling conditions are discussed below briefly to improve the realisation of this statement.
- The discharge permit condition is for “use and discharge” of all products or substances.
- The air quality administrative norm, or threshold limit, for oil mist for a 12-hour work shift is 0.60 milligrams per cubic meter, and 0.30 milligrams per cubic meter for oil vapour.
- Drilling conditions are becoming increasingly challenging, requiring drilling fluids with lower rheology profiles for more sensitive geological formations and/or slimmer hole designs.
The discussion regarding challenges presented owing to regulations and drilling conditions can start with the base oil selection.
Base oils can be derived from many sources, including vegetable oils. Typically, they are of paraffin or kerosene sources. ConocoPhillips Scandinavia uses base oils of paraffin sources owing to their reduced volatility.
The base oils used are highly refined from specific raw material stocks. In the Greater Ekofisk area, the base oil is of a standard to where it is used in food and cosmetic products. In addition, the range of carbon compounds are controlled and the kinematic viscosity of the base oil relatively high.
The high viscosity characteristic is physically required in order to gain a lower headspace. This is significant for improved work environments, yet carries a technical compromise. While the vapour emissions are reduced, the higher kinematic viscosity results in a formulated non-aqueous fluid that has an overall higher rheology profile.
This higher viscosity can result in higher, sometimes excessive, pressures while circulating the drilling fluid. The pressures can break down the formation being drilled, causing an uncontrolled event. This could include losses of non-aqueous fluid to the formation, eventual gas or hydrocarbon intrusions, or even a mechanical failure of the wellbore itself. Therefore, selecting the base oil must involve careful consideration of the work and marine environments, as well as the technical limitations of the operations.
The emulsifiers and oil wetting products used in non-aqueous fluid systems are, by nature of their function, potentially hazardous to the environment. However, studies have shown that the “carrier” fluids used to suspend the active ingredients can be significantly more volatile. Recent improvements were made to address this issue. However, studies the company conducted in 2000 indicated that the volatility of an emulsifier could be up to 37.7 times greater than for the base oil (Table 1).
Since 2004, more marine and work environmentally acceptable products have been developed. Their application must be conducted cautiously because, in their early development phases, their functional quality in a NAF system was not acceptable. The use of the new products in a non-aqueous fluid system destabilized the flow properties of the fluid system with the result that the quality of the fluid could not be controlled adequately for secure drilling operations. More recently this problem has been overcome.
A critical function of the non-aqueous fluid system is that the cuttings produced while drilling must be transported by the fluid from the hole. In the mid-1990s, specialty products were provided to enhance this function in non-aqueous fluid systems. However, they were environmentally classified “black” within the Norwegian classification system. The use of a “black” product is to be avoided except in an extreme technical case.
As the use of the rheology modifiers was beneficial but not absolutely necessary, their use was discontinued in the late 1990s in Norway owing to their environmental classification. The result was that compensation measures were required within drilling operations. The compensatory initiatives cause loss of operational time with the result of significantly increased costs.
Today the industry still struggles with this challenge. Drilling fluids contractors are unable to provide rheology modifiers that are environmentally acceptable for use in non-aqueous drilling fluid systems; therefore, drilling operations continue to be compromised.
Barite-free spud mud
ConocoPhillips Scandinavia has new platform campaigns where surface conductors are drilled into the formation immediately below the sea bed. At this stage, no riser pipe is connected to surface. This means all pumped fluids and cuttings are deposited on the sea bed. This is the case with all offshore operations.
For the operation, sea water mixed with pre-hydrated bentonite is pumped to clear the hole of formation cuttings. For periods where the well is to remain static, a “spud mud” sea water-based fluid using bentonite for increased viscosity and barite for increased density is pumped into the well to keep it from collapsing or caving in. This spud mud eventually is discharged to the sea bed.
Barite contains heavy metals – undesirable on the sea bed. The company developed a barite-free spud mud that uses environmentally acceptable polymers, such as poly-anionic cellulose and xanthan gum polymers with a brine fluid base for increased density. If the fluid’s density need to be raised even higher, ground calcium carbonate is used. In this way, the heavy metal discharges are reduced by a factor of 35.
The barite-free spud mud requires additional logistics handling and costs 30% more than a conventional barite spud mud would, but significant environmental exposure to heavy metals is avoided.
- The Hazardous Substance Management System considers products and substances from introduction to final use.
- The system requires that occupational health, environmental and technical specialists communicate and agree.
- Improvements are made by constantly challenging HSE and technical conditions.
- The improvements provide ConocoPhillips Scandinavia, suppliers and manufacturers with industry-leading products and operation conditions.
- The company’s industry-leading position has provided some commercial advantages and control.
- A constructive collaboration is maintained among all stakeholders, including Norwegian authorities.
These developments over the last 15 years have proven that collaboration between suppliers and end users can result in significant improvements in HSE performance without compromising technical performance.
Article acknowledgements and references are available online at dev4.iadc.org.
Reagan James is senior fluids adviser and Hanne Størksen is environmental engineer for ConocoPhillips Scandinavia AS.
This article is based on a presentation at the 2009 IADC Environmental Conference & Exhibition, 12-13 May, Stavanger, Norway.