Clay-free invert emulsion fluids (IEF) can offer reduced potential for barite sag, improved rate of penetration, low equivalent circulating density and substantial decreases in surge/swab pressures. The unique properties of these fluids are achieved by omitting organophilic clay used to stabilize emulsions in conventional IEFs, and instead relying upon robust emulsifiers, colloidal solids and shear. Clay-free IEFs are generally built using a “seed” fluid that has been exposed to high shear levels by travelling through the bit. High shear helps form an extremely stable emulsion, allowing the seed mud to help stabilize fresh built fluid at the liquid mud plant. Occasionally a fluid may need to be built without using seed mud. Unless properly mixed, these fluids may exhibit lower stability, leading to top oil separation and barite sag. This paper details an extensive investigation into the effects that emulsifier concentration, addition of colloidal fines and shear have on the stability of laboratory, mixing plant, and field-tested invert emulsion drilling fluids. Fluid stability is intricately linked to emulsion stability, which is directly related to the shear history of the whole fluid, the viscosity of the external phase, the emulsifier type and colloidal solids loading. Optimizing these properties can lead to more stable fluids that exhibit stronger gels and lower sag tendencies. Therefore, a mud built “from scratch” should be exposed to high shear, contain the appropriate amount of emulsifier and if possible, contain a small loading of colloidal fines. A series of field cases demonstrates how these modifications have led to improved fluids that remain stable from initial mix to delivery at the wellsite and commencement of drilling.

Deepwater production well design and equipment installation presents a host of challenges for operators. One of the major problems is the uncontrolled heat transfer to outer annuli and heat loss from the production tubing which can be detrimental to the integrity of outer annuli. This can reduce the well productivity in case deposition of paraffin and asphaltenes occurs, and could contribute to the formation of gas hydrates. Vacuum insulated tubing (VIT) has had limited success but has numerous drawbacks (e.g., cost, breakdown, "hot spots" at connection joints, etc.). To avoid these problems, high viscosity insulating packer fluids (IPFs) have been employed to thermally isolate production tubing from the exterior pipe and to provide the required hydrostatic pressure. Numerous combinations of both water- and oil-based materials have been utilized in attempts to devise a cost effective solution. Successful fluids have a low inherent thermal conductivity, remain viscosified or gelled to eliminate convective heat transfer and are expected to have service lifetimes of up to 20 years. However, the current state of the art falls short of meeting these objectives. Oil-based IPFs often have low thermal conductivity, but cannot be weighted, suffer from toxicity and often come with HSE issues. Water based IPFs can be weighted, but generally have temperature stability limitations > 250°F (121.1°C) as well as higher inherent thermal conductivity than oil-based IPF's. Through extensive investigation of multidisciplinary technologies, a superior performing aqueous-based IPF was developed for elevated temperatures. The novel system delivers performance beyond conventional systems of comparable thermal conductivity (k). The new system covers a density range of 8.5 - 14.6 lb/gal (1.02 - 1.75 sp.gr.) and displays heat transfer measurements between 0.12 – 0.17 BTU/hr ft°F. High-temperature static aging tests have demonstrated superior gel integrity with no phase separation or syneresis after exposure to 280°F (137.8°C) for three months. Parallel testing at 325°F (162.8°C) has shown similar success. The new fluids are hydrate inhibitive, pass oil and grease testing, and can be made environmentally acceptable for the Gulf of Mexico. Laboratory data generated under deepwater simulated conditions will be presented and discussed in this paper. Introduction In thermal physics, heat transfer is the passage of thermal energy from a hot to a cold body. When a physical object or fluid is at a different temperature than its surroundings or another object, and is put into "thermal contact", transfer of thermal energy occurs to the extent that the surroundings reach thermal equilibrium. Heat transfer constantly occurs from a hot entity to a cold one (described by the second law of thermodynamics). Classical transfer of thermal energy occurs through conduction, convection, radiation or any combination of these. Heat transfer associated with carriage of the heat of phase change by a substance (i.e., steam which carries the heat of boiling) is sometimes considered a type of convective heat transfer.1–2 Conduction is the transfer of thermal energy from a region of elevated temperature to a region of lower temperature through direct molecular communication within a medium or between media in direct physical contact without a flow of the material medium. The transfer of energy can proceed by elastic impact as in fluids, free electron diffusion as predominant in metals, or phonon vibration as predominant in insulators. In other words, heat is conveyed by conduction when adjacent atoms vibrate against one another, or as electrons move from atom to atom. Conduction is superior in solids, where atoms are in constant contact. In liquids (except liquid metals) and gases, the molecules are usually further separated, decreasing the chance of molecules colliding and passing on thermal energy. Conduction does not transpire in an ideal vacuum. Thermal conductivity (i.e., conductivity constant or conduction coefficient, k) is employed to quantify the ease at which a substance conducts thermal energy.1 Convection is a combination of conduction and the transfer of thermal energy by fluid circulation of warm particles in bulk to cooler areas in a material medium. Unlike the case of pure conduction, currents in fluids are also involved in convection. This movement occurs into a fluid or within a fluid, and cannot happen in solids. In solids, molecules keep their relative position to such an extent that bulk movement or flow is prohibited, and therefore convection does not occur. Convection occurs in two forms: natural and forced convection. In natural convection, fluid surrounding a heat source receives heat, thereby rising due to decreased density.

The water reactivity of clay-containing shale minerals remains a long-standing problem when drilling wellbores with water-based fluid systems. Complicating this issue, the environmental effect of chemical additives used in water-based drilling fluids continues to receive heightened scrutiny in various regions across the world. This study addresses these challenges by expanding the molecular toolbox of environmentally friendly additives that are available to manipulate shale reactivity. To this end, a shale inhibitor package is introduced and discussed that leverages chemical synergy to impede the uptake of water in shale minerals while also increasing the structural integrity of shale cuttings. The main component, a natural-based hybrid organic/inorganic inhibitor blend, is highlighted. Simple fluids systems were prepared with potassium-based brines and combined with shale inhibitors for initial shale erosion screening experiments. These simple fluids isolated the shale inhibition effects of the inhibitors of interest and excluded the possible influence of additional chemical additives typically found in drilling fluids. Subsequently, fully formulated, water-based drilling fluids were prepared with these inhibitors and compared to fluids with traditional inhibitors. These fully formulated drilling fluids were characterized by rheological testing, fluid loss, shale erosion, accretion, and linear swell testing. An inhibitor combination of a hybrid organic/inorganic inhibitor blend, along with a nitrogen-rich oligomeric hydration suppressant, was determined to be the most effective inhibition mixture in simple fluid screening. The dual mode of action of the two inhibitors, disparate in both molecular size and chemistry, likely achieved optimal interfacial shielding on the clay minerals to effectively diminish the rate of reaction with water. More importantly, the shale inhibition was successfully translated to fully formulated fluid systems without affecting rheological properties or diminishing fluid loss control. The results achieved were comparable to a current high-performance, synthetic-based shale inhibitor; however, the new shale inhibitor package features a more favorable environmental profile. Natural-based materials and their derivatives are continually revealed to contain useful properties, particularly for water-based drilling fluids. In this study, high-performance functionality and environmental friendliness were united with an innovative natural-based hybrid organic/inorganic inhibitor blend that is believed to function by encapsulating shale minerals. In addition, a synergy was discovered between hybrid organic/inorganic inhibitor blends and nitrogen-rich oligomeric compounds. Ultimately, the materials developed have achieved yellow environmental ratings in the North Sea and have been successfully validated in field applications in Norway.

Disposal of drill cuttings from non-aqueous drilling fluids (NAF) can be a significant expense and logistical issue for the operator of a drilling rig. NAFs typically contain high levels of salts, commonly calcium chloride or sodium chloride, in the internal phase of the emulsion. These salts are highly beneficial for wellbore-stabilization performance, but pose issues for the disposal of drill cuttings because the salts do not biodegrade and can accumulate in high concentrations in soil. A salt-free NAF has been developed and field validated in the Western Canadian Sedimentary Basin in Alberta, Canada. The system uses a biodegradable organic to provide an internal phase with equivalent water activity to traditional salt-containing systems. This results in a fluid system with the performance and benefits of a conventional NAF, while potentially allowing for greater cuttings disposal options. Depending on local regulations, the system has the potential to reduce environmental and long-term liability concerns by being able to land-farm drilled cuttings without hindering plant growth. Three wells on a seven-well pad were drilled with the salt-free NAF; the other four were drilled with a conventional invert emulsion fluid (IEF). Cuttings from one of each type of well were collected. A bioremediation study was conducted to analyze the cuttings for electrical conductivity and plant growth. Cuttings were delivered to the lab for testing and analysis. Laboratory testing showed that when mixed with top soil, the salt-free cuttings allowed for viable plant growth; whereas, the conventional cuttings did not allow for plant growth. This paper will discuss in detail the bioremediation study of the salt-free NAF. A salt-free NAF has been developed in the lab and successfully validated in the field. Cuttings from the salt-free system showed superior plant growth when compared to conventional, salt-containing systems. This system is expected to offer expanded options for cuttings disposal and, ultimately, reduce the cost and liability associated with using NAFs in many areas.

Maintaining the integrity of the drilling-fluid column is vital for safety and operational efficiency. Stable, controlled fluid density provides a primary pressure barrier during the drilling phase. Non-aqueous fluids (NAFs) provide huge benefits for nearly all aspects of difficult drilling situations, yet still can have challenges related to weight suspension. The geometry and annular restrictions of modern well designs often demand low fluid rheology parameters to avoid excessive circulating pressures, and this unsurprisingly increases the risks of sagging weight material. Given the importance of understanding the fluid behaviors in these situations, operators and service companies have made significant efforts to develop reliable sag testing methods. Older methods of testing neglected movement and instead centered on mimicking the downhole conditions such as temperature and hydrostatic pressure. Variations of this static aging method addressed the critical angle where Boycott settling accelerates the sag. More complex, dynamic methods were devised later in time to provide greater insight on sag behaviors. Although engineers and scientists have made numerous strides to create a definitive sag test, the current tests have limited capabilities. Very few are capable of working in an offshore environment. Sag events continue to be costly and problematic to operators’ main objectives of drilling and completing their wells safely and efficiently. The authors address results from the current state of the art in sag testing and compare these to a proprietary dynamic procedure created in 2019. While the method is still in development, its capabilities have been well defined. Fluid samples are kept in constant motion at low-ranging shear rates and elevated temperatures to simulate sag-prone conditions downhole. Results indicate a high degree of correlation to the expected sag with different sizes of barite in low-ECD fluids.