Drilling Fluids that are water based, acts as a High–Performance Filtration Control Agent when Gilsonite is added. A generic name widely used for a black, lustrous, carbonaceous resin classified as an Asphaltite. Its proper name is Uintaite, and it is found in Utah, USA. An important characteristic of Gilsonite is its softening–point temperature. In Oil–Base Muds (OBM), it is used as a fluid–loss control agent.
In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. One of the functions of drilling mud is to carry cuttings out of the hole.
The three main categories of drilling fluids are: (1) Water–based muds (WBMs), which can be dispersed and non–dispersed; non–aqueous muds, usually called (2) Oil–based muds (OBMs); and gaseous drilling fluid, in which a wide range of gases can be used. Along with their formatives, these are used along with appropriate polymer and clay additives for drilling various oil and gas formations.
The main functions of drilling fluids include providing hydrostatic pressure to prevent formation fluids from entering into the wellbore, keeping the drill bit cool and clean during drilling, carrying out drill cuttings, and suspending the drill cuttings while drilling is paused and when the drilling assembly is brought in and out of the hole. The drilling fluid used for a particular job is selected to avoid formation damage and to limit corrosion.
General description of drilling fluids loss control (FLC):
Gilsonite improves drilling efficiencies, wellbore stability, filter cake development and more. As an integral component of premium drilling fluid products, Gilsonite actively improves drilling efficiencies while reducing costs and minimizing the HSE impact associated with most drilling fluid additives.
Gilsonite or Natural Asphalt has long been used in oil fields as a fluid loss additive in drilling fluids. In numerous grades and formulations, Gilsonite has been utilized to fight borehole instability complications, offer lubricity particularly in greatly diverged holes. It is also a bridging instrument to contest differential pressure sticking and deliver a less invasive coring fluid. It has scientifically been proven that suitably framed Gilsonite products can minimize collapsing in foundations comprising of water–sensitive sloughing shales, and diminishes stuck pipe problems by creating a thin wall cake and an inter–matrix filter cake. Gilsonite products are broadly employed worldwide in water based, oil based, and synthetic based mud systems. Furthermore, Blended Gilsonite (Natural Asphalt) is effectively utilized in all water–based systems.
Drilling fluids loss control component appears to be particularly important to Fluid Loss Control (FLC) and to act as a shale inhibitor. This loss control by itself would tend to cause an increase in fluid viscosity but this is effectively dealt with by the other components which make up the additive of the invention.
The invention relates to a composition comprising an HP/HT fluid loss control aid, stable at elevated temperatures and which also acts as an excellent shale stabilizer, bore hold lubricant, sealant for depleted sand, and wall cake conditioner. The HP/HT fluid loss control aid broadly comprises a Gilsonite (natural asphalt) which also contains a surfactant such as a nonionic surfactant. The HP/HT fluid loss control aid also contains solubilized lignite such as causticized lignite and carbon black. The fluid loss control aid reduces HP/HT filtrate loss, has good stability at elevated temperatures such as at 148 ºC (300 °F), stabilizes troublesome shales and decreases borehole erosion, helps seal depleted sands, reduces torque and drag, causes no adverse effects on the flow properties of the properly conditioned drilling fluid, and lowers total well costs.
To achieve these and other advantages, and in accordance with the purpose of the invention, as embodied and broadly described, the invention comprises a composition comprising an HP/HT fluid loss control aid stable at elevated temperatures, and which also acts as an excellent shale stabilizer, borehole lubricant sealant for depleted sands, and wall cake conditioner. The HP/HT fluid loss control aid broadly comprises Gilsonite, an asphaltic material or solidified. The Gilsonite employed according to the present invention also contains a surfactant, especially, a nonionic surfactant.
As indicated earlier, the additive of the invention comprises the product obtained by reacting together in the presence of water, Quebracho, Lignite, Fluid Loss Control (FLC), Sodium Sulfite (Sodium Sulphite), Paraformaldehyde (PFA) which is the smallest Polyoxymethylene, the polymerization product of formaldehyde with a typical degree of polymerization of 8–100 units and sodium hydroxide (Caustic Soda) which is an inorganic compound with the formula NaOH. Each of the indicated components is essential to obtain optimum results according to the invention.
The reaction conditions used to make the product of the invention can be fairly widely varied. Usually, however, the product is prepared by heating the indicated components in a sealed reaction vessel at a temperature in the order of 100 ºC (212 ºF) – 150 ºC (302 ºF) for a period of 120 – 30 minutes. Shorter times can be used as the temperature is increased. It appears that the reaction results in sulphomethylation and causticization of a complex formed between the Quebracho are a common name in Spanish to describe very hard (density 0.9 – 1.3) wood tree species. The etymology of the name derived from Quiebrahacha, or Quebrar Hacha, meaning “Axe–breaker”, Lignite, often referred to as Brown Coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has carbon around 25% – 35%, and is considered the lowest rank of coal due to its relatively low heat content. Lignite is mined all around the world and is used almost exclusively as a fuel for steam–electric power generation and Asphaltite although the chemistry involved is highly complex and not fully understood. In any case, the resulting composition, which is essentially water–soluble, is preferably dried and may be stored for subsequent blending with conventional clay–based aqueous drilling dispersions or drilling fluids. This blending advantageously is carried out on site although it will be appreciated that the additive may be pre–packed with the drilling fluids.
Functions of Drilling Fluid loss control (FLC):
- Remove cuttings from the well.
- Control formation pressure.
- Suspend and release cuttings.
- Suspend and release cuttings.
- Seal permeable formations.
- Maintain wellbore stability.
- Minimize reservoir damage.
- Cool, lubricate, and support the bit and drilling assembly.
- Transmit hydraulic energy to tools and bit.
- Ensure adequate formation evaluation.
- Control corrosion
- Facilitate cementing and completion.
- Minimize impact on the environment.
- Prevent gas hydrate formation.
Gilsonite is the only drilling fluids additive that provides all of these benefits:
- Provides wellbore strengthening matrix
- Controls fluid loss and seepage
- superior shale stabilization
- Prevents lost circulation
- Strengthens the wellbore to increase wellbore stability
- Minimizes differential sticking
- Reduces or eliminates lost circulation
- Promotes effective filter cake development
- Performs in oil–and water–based drilling muds
- Performs in HP/HT environments
- Minimizes HSE risks
Unique bonding and plugging properties prevent formation damage:
Gilsonite forms a physical and chemical bond with permeable formations, creating an effective seal to prevent the passage of drilling fluid. By uniquely functioning as both a malleable and solid plugging agent, Gilsonite controls fluid loss and seepage, prevents lost circulation and protects reactive and low–reactive shale surfaces, even at elevated bottom hole temperatures.
Proven to strengthen the wellbore:
High Pressure (HP) / High Temperature (HT) wells, are those where the undisturbed bottom hole temperature at prospective reservoir depth or total depth is greater than 150 °C (302 ºF), and either the maximum anticipated pore pressure of any porous formation to be drilled through exceeds a hydrostatic gradient of 0.8 psi/ft., or a well requiring pressure control equipment with a rated working pressure in excess of 10,000/psi. Shales and under pressured zones requires specialized drilling fluids and wellbore–strengthening techniques. Adding Gilsonite to an Oil–Based Mud (OBM), Sand–Based Mud (SBM) or Water–Based Mud (WBM) strengthens the well by (Refer to Fig 3):
- Reducing pore pressure transmission and sealing micro–fractures in shale and low–porosity sands.
- Keeping inter bedding formations intact.
- Developing effective filter cake.
- Providing a “Smear Effect” that creates a continuous protective sealant along the wellbore wall.
The most effective additive to prevent differential sticking:
Gilsonite minimizes the occurrence of stuck pipe and stuck logging tools by thoroughly sealing permeable formations – even in zones with a highly overbalanced pressure differential – and improving filter cake lubricity.
Health, safety, and environmental advantages:
Naturally, occurring Gilsonite has significant health advantages over synthetic products.
- Non–toxic (Unlike coal or fly ash)
Gilsonite offers significant cost advantages in both OBM and WBM applications:
Compared to alternative products, Gilsonite offers comparable or superior performance at a much lower cost. In water–based mud (WBM) applications, Gilsonite’s performance compares favorably with Sulfonated Asphalts while costing 25–50% less.
In HP/HT environments using synthetic–based mud (SBM), Gilsonite provides a cost reduction of more than 80% compared to premium co–polymer, while the high softening point of Gilsonite also results in a 45% reduction in fluid loss.