The quality of drilling fluids and accompanying drilling waste represents major cost and efficiency issues in today’s price-sensitive drilling environment—particularly with the current low oil prices. Drilling fluids play several vital roles in drilling operations: cooling and lubricating the drill bit, carrying drill cuttings to the surface, controlling pressure at the bottom of the well and ensuring formation retention. From an operational drilling perspective, effective fluids can contribute to increased rates of penetration (ROP), reduced equivalent circulating density (ECD) and minimized nonproductive time (NPT).
From a waste perspective, retaining the quality of drilling fluids and the optimal separation of solids can reduce the volume of drilling fluids lost and minimize the tonnage of drilling waste generated, with significant savings in waste disposal and meeting environmental obligations. In addition, cleaner drilling fluid reduces the need for premix chemicals.
Existing Technology Limitations
In most cases, the effectiveness and quality of drilling fluids remain dependent on solids-control technologies. Too often, these technologies are rooted in the past. For many years, shale shakers have been the preeminent technology offshore and onshore for maintaining drilling fluids and separating solids. The vibration and high G-forces emanating from the shale shakers cause solids to be filtered out for discharge or treatment. The cleaned mud then returns to the active fluid system.
But shale shakers come with limitations. For example, the high G-forces are often too efficient, breaking down the drilled solids into extremely fine particles. This process makes the solids more difficult to remove, increasing solids content in the drilling fluids, which leads to a decline in drilling fluid efficiency with a negative impact on ROP and ECD. The lack of separating efficiencies is particularly apparent when working with low-gravity solids content—drilling deeper and extended-reach drilling (ERD) wells, for example.
Additionally, vibrating shale shakers often cause high volumes of mud to be lost, which generates drilling waste and reduces the amount of mud that can be reused within the system. These inefficiencies have an environmental and financial impact because the cost of drilling waste management is rising. Industry analysts at Markets and Markets estimate that the onshore and offshore drilling waste management market will grow from $5.3 billion in 2014 to $8.7 billion by 2019. On the Norwegian Continental Shelf, the treatment and disposal of drilling waste is conservatively estimated at $1,580 to $1,750 per ton. Onshore costs for waste disposal are also significant.
There is a clear need for reducing costs and improving the process for separating drilled rock particles from the fluids. Operators want optimal drilling fluid and drilling performance, a smaller volume of lost mud, and a reduction in the total tonnage of drilling waste generated.
An Enclosed Solids-Control System
One company developed an enclosed solids-control system that eliminates the traditional process of shaking fluid and solids and replaces it with an enclosed, vacuum-based filtration process. Rather than relying on high G-forces, the new system vacuums drilling fluids through a rotating filter belt by using high airflow to separate the cuttings from the fluid. The cleaned drilling fluids are then returned to the active mud system, and the drilled solids are carried forward on the filter belt for discharge or removal. The high airflow also preempts the need for expensive mud coolers and is particularly applicable in high-pressure/high-temperature wells.
Water-knives are installed on the inside of the vertical part of the filter belt to remove any cuttings or sticky clay that may have stuck to the belt. Pneumatic micro-vibrators are installed underneath the filter belt to create resonance and improve conductance. The solids removal efficiency of the new system is often as high as 90 percent.
So what does this mean for operators?
The improved separation capabilities lead to better quality mud and fewer chemicals required to maintain its properties. One operator and mud company recently reported that the reduced use of premix chemicals brought savings of $270,000. These improvements led to enhanced drilling efficiencies through stable mud properties, higher ROP, reduced stuck pipe incidents and a decrease in NPT.
With more mud recycled back to the fluid system, there is less waste, and that waste is cleaner. The new solution also generates substantially drier cuttings with mud on cuttings being reduced to less than 30 percent of drilled solids, and oil on cuttings as low as 5 percent. These drier cuttings and lower oil content mean that disposal is cheaper. In the Gulf of Mexico, for example, the regulatory limit for oil on cuttings to allow for the disposal of cuttings directly to the sea is 6.9 percent—well above what the new system can produce.
Another benefit from the use of vacuum and airflow rather than high G-forces is an improved working environment. The area is free of noise, vibrations, and exposure to both oil vapor and mist.
This new system has been deployed both onshore and offshore in Europe, the Middle East, the Far East, and North and South America. In one such installation on the Maersk Giant rig—a jack-up drilling rig based in the North Sea—the new system replaced four traditional shale shakers, leading to improved drilling efficiencies with less drilling fluid lost and more returned to the mud tanks for reuse. With this installation, the cuttings have a low mud content for easier and cheaper disposal. In one selected well, where only 27 tons (17 cubic meters [m3]) of drilling fluid waste was generated, the estimated oil on cuttings was just 1 to 5 percent by weight.
The solids-control system is equally applicable onshore, where the rise in drilling costs and declining oil prices have increased operator needs to monitor the bottom line as well as meet stringent environmental controls.
In a cost-conscious sector occupied by larger operators and smaller independents, the system will provide onshore operators and drilling contractors with improved operational efficiencies and reduced solids-management and mud treatment costs. Initial cost analysis based on various land operations from a fluid cost and disposal standpoint shows the system reducing overall operating expenses by as much as 15 percent per well.
The new system also can boast improved HSE outcomes compared with shale shakers. This was one of the main drivers behind an onshore Middle East trial with a major operator that was successfully completed in 2014. The primary operator objective was to improve the working environment, minimize the consumption of consumables (filter belts), and reduce mud losses and the corresponding volume of drilling waste produced.
In this case, noise levels were reduced, filter belt consumption was less than the targets and mud-on-cuttings concentrations were reduced to less than 30 percent by volume of the rock drilled. Solids removal efficiency was also above 90 percent.
A Modern-Day Solution
The focus on the bottom line will ensure that drilling fluids and waste management technologies remain high on the agenda for operators for years to come. Operators have a modern-day solution to choose.