Published in Pipeline Magazine, August 2019.
By Robbie Pond, TWMA Regional Director - KSA & Pierre-Marie Hinden, TWMA Business Development Manager - UAE.
In the UAE, Federal Law No 24 of 1999 for the Protection and Development of the Environment prohibits the discharge of any polluting substance resulting from drilling, exploring, testing of wells or production into the water or land, unless appropriate measures are taken to safeguard the environment.
To fully comply with this regulation and optimize its drilling programme, a major oil operator in the Middle East, commissioned TWMA to perform integrated drilling waste management services on the second largest oilfield in the region, also the fourth largest in the world.
This covered all elements of collection, transportation, segregation and treatment of the various materials produced, including drill cuttings, piling waste, slops, cement and excess fluids.
Given this field was a ‘zero discharge’ area the safest and most cost effective method was to combine offshore thermal treatment with cuttings re-injection (CRI) to create the world’s first offshore self-contained solution.
Field proven thermal desorption technology
Thermal desorption technology is the process of using heat generated from kinetic energy to separate the three constituent parts of the non-aqueous drilling fluid (NAF) drill cuttings (oil, water, and solids) and remove hydrocarbon content.
Using a hydraulically operated positive displacement piston pump, a cylindrical mill within the TCC RotoMill® chamber grinds a bed of solids causing kinetic energy creating heat through friction.
Once the mill reaches a pre-determined temperature set to suit the evaporation properties of the particular base oil, the NAF is fed into the chamber causing the liquids (oil and water) to flash evaporate from the solids. The resulting gases then exit the mill and pass through a cyclone, where any fine solids particles are removed prior to gases travelling to the oil and steam condensers, respectively. The liquids are then recovered as base oil and water from the condensers. During the process, solids are collected from the mill and cyclone and disposed of along with the recovered water via cuttings re-injection (CRI).
To ensure that optimum conditions and an even flow are maintained throughout the process, the entire operation is controlled at all times by the programmable logic controller (PLC) control system. Critical temperatures and pressures are monitored and regulated using data from temperature thermocouples and pressure transducers. The system also boasts the ability to store historic trends from the process for evaluation at any time.
The throughput of the TCC RotoMill® is proportional to the amount of energy that is imparted into the bed of solids within the mill chamber. Basically, the more energy applied to the solids, the greater volume of liquid content is evaporated. This in turn increases the throughput of the NAF drill cuttings. Throughput is also governed by the physical properties of the NAF drill cuttings such as the oil/water/solids ratio, rock formation type and temperature of the feed material.
Recovery, recycling and re-use
The TCC RotoMill® is designed to recover 99.9% of the hydrocarbon content of NAF drill cuttings resulting in the remaining recovered solids containing less than 1% (typically less than 0.1%) hydrocarbon content by weight. Recovered water is compliant with the operator’s disposal requirements of <300 ppm (typically < 20ppm). The mill produces three distinct outputs:
- Oil - The recovered oil is reused in the drilling fluid system as it retains the physical properties found in the drilling mud due to the pre-determined temperature within the mill chamber
- Water - The recovered water is discharged and is typically <20ppm hydrocarbon content. This is well within the operator’s regulatory requirements. The water is mixed with the solids and re-injected into the disposal wells
- Solids - The recovered solids have a hydrocarbon content of less than 1% and typically less than 0.1%. These solids are disposed of using CRI.
TWMA design, manufacture, own and operate a fleet of units delivering power up to 1400Kw achieving field proven throughput of 10Mt per hour of drill cuttings. These units have been deployed in contrasting geographical locations with varying temperatures from -51oC (-59.8oF) in North Dakota to more than 55oC (131oF) in Abu Dhabi with humidity of 100%.
Economic, safety environmental gains
For the Middle East deployment, TWMA’s solution included the installation of a TCC RotoMill® unit in four separate drilling locations to process the drilling waste produced by two land rigs to an on-site tank farm. Here, the material was segregated and treated prior to being transferred to CRI. Installing one TCC RotoMill® per site meant all drilling waste was contained and processed on site.
Since 2012, the company has successfully handled more than 2.5m barrels of drilling waste using its proprietary bulk cuttings storage and handling system. It has also processed 173,000MT of NAF drill cuttings, recouped USD24m worth of base oil which was reused in the drilling mud system, and allowed the recovered solids and water to be re-injected.
The remaining hydrocarbon in solids has been on average approximately 0.15% by weight, significantly lower than the regulatory 1% requirement that the operator had stipulated. On average, the hydrocarbon content of the recovered water is 15ppm, again, well within the operator’s 300ppm stipulated discharge limits.
Most importantly, it has eliminated the need to lift and transport 125k skips back to shore, significantly increasing personnel safety and the potential impact of cost and delays on drilling. Over six years, the campaign has so far achieved 2.5m hours free of lost time injury (LTI).
Environmentally, the project has achieved the aim of meeting and exceeding the environmental regulations set out by the operator. As there has been no mainstream drilling returns sent to land for disposal or landfill, the operator has been able to optimize its drilling program by avoiding potential rig non-productive time (NPT). Notably, there are no harmful emissions from thermal desorption technology to the atmosphere.
The results from this project have demonstrated that using an integrated, at source solution to treat drilling waste is not only viable, but also highly successful. Tangible cost savings, exceeding environmental regulations and optimizing the drilling programme have contributed to this success.
Link to article https://bit.ly/2KgCu0c (page 30-32)