Drilling fluid separation & it’s environmental issue DESALEGN YESHITILA NUGROHO ADI SASONGKO

1. Solid control history 2. Functions of drilling fluid 3 1. Solid control history 2. Functions of drilling fluid 3. Solids control equipment 4. Environmental impacts

History of solid control Drilling fluid maintenance cost, clean up & disposal cost as well as the over all cost of boring, can be reduced dramatically when proper solids control techniques are utilized. These facts were recognized in the oil industry in the late 1800’s. When open earthen pits we used to separate the cuttings from the borehole. This was accomplished by a series of weirs and settling pits that allowed the solids to naturally settle out by using gravity. The clean mud then flowed into a suction pit to be re-pumped down hole. This was the first solids control technique ever used

Functions of drilling mud to control subsurface pressures, lubricate the drill bit, stabilize the well bore, and carry the cuttings to the surface, among other functions. Mud is pumped from the surface through the hollow drill string, exits through nozzles in the drill bit, and returns to the surface through the annular space between the drill string and the walls of the hole

Benefits of low solids in drilling Mud Increased drilling penetration Increase bit or back reamer life Reduce mud cost Reduce triplex mud pump, mud motor & surface equipment maintenance cost. Reduced clean up & haul off or disposal cost

Mud Circulating System

Solids removal theory Drilling fluid and equipment maintenance cost can decrease greatly when proper solids control practices are utilized. From a fluid control stand point it would be desirable in most cases to remove all drilled solids. Although this is possible, it would be cost prohibitive. The goal of a solids control system is to achieve the balance between mechanical solids separation and dilution that will result in drill solids being maintained at an acceptable level with a minimum of cost

Particle size and effects - Drilled solids are those particles that enter the mud system in the form of cuttings from the bit or back reamer or from borehole debris. These solids vary in size from less than one micron & larger depending on the carrying capabilities of the drilling fluid. - Drilling fluid is classified as water base utilizing water as the liquid phase. The solid phase of any drilling fluid is either commercial solids or drilled solids. Most commercial solids such as bentonite have a relative particle size of less than one micron. (.000039 inches).

Methods of controlling solids Mechanical treatment Chemical treatment Dilution of mud with water Discard mud & mix new mud

Mechanical separation basics Mechanical separation equipment employs mass differences, size differences or a combination of both to selectively reject undesirable solids and retain desirable drilling fluid.  The desanders and desilters utilize centrifuge force and mass difference between the solids density and liquid density for solids removal. The shale shakers employ a vibrating screen of various micron-sized differences.

Basic Equipment of Mud Solid Control Shale shaker Desander Desilter Hydrocyclone Mud cleaner

Shale shaker One method of removing solids from drilling mud is to pass the mud over the surface of a vibrating screen. Particles smaller than the openings in the screen pass through the holes of the screen along with the liquid phase of the mud. Particles too large to pass through the screen are thereby separated from the mud for disposal. Basically, a screen acts as a “go-no-go” gauge:  Either a particle is small enough to pass through the screen or it is not.

Decanter

Hydrocyclones Hydrocyclones are simple mechanical devices, with out moving parts, designed to speed up the settling process. Feed pressure is transformed into centrifugal force inside the cyclone or cone to accelerate particle settling in accordance with Stoke’s Law #1. In essence, a cyclone is a miniature settling pit which alloys very rapid settling of solids under controlled conditions.

Environmental Issue of drill cutting

During drilling operations, two types of drilling waste are created: Cuttings (rock mass) and useddrilling mud. Drilling fluid will always be attached to cuttings. The industry uses three types of drilling fluids, all with different technical and environmental properties. The authorities’ requirements related to the disposal of waste are linked to the following properties: Oil-based drilling fluids (OBM): Have in most cases the best technical properties. The authorities do not permit the discharge of OBM and cuttings drilled with oil-based drilling fluids. Cuttings and fluids are taken to shore. Water-based drilling fluids (WBM): The authorities permit the discharge of used drilling fluid and cuttings upon application. Synthetic drilling fluids (SBM): Based on ether, ester or olefin. They have technical properties that are similar to oil-based drilling fluids in many ways. Discharge of used SBM is not permitted, but the discharge of cuttings may be permitted upon application. The use of water-based drilling fluids has increased by 20 per cent from 2005. There have not been any reports of the use of synthetic drilling fluid in 2006, while the use of oil-based drilling fluids has been reduced by 16 per cent.

Treatment of drill cutting Discharge (Offshore)/Disposal to sea - If the cuttings are considered low environmental risk and depending on local regulations, they can be disposed into the sea in certain regions. However, most require some pre-treatment to reduce the oil-on-cuttings to less than 6.9% by volume on a wet weight basis. 2. Transportation to Shore Injection - In the injection process, the cuttings are converted into slurry, which is then pumped into a receiving formation at pressures exceeding the fracture gradient.

Environmental Issue The dryness of the cuttings aids disposal or re-use.

Drill Cutting Transportation

In previous picture is shown the new designed platform supply vessel ST216 with 8 integrated structural tanks under deck for drill cutting of total abt. 430 m3. Number of tanks can be adjusted to suit actual capacity requirements. To day handling of drill cutting give a potential hazard to following: * Possible pollution to sea through disposal on sea bed * Potential spillage to sea * Safety risk for personnel through extensive manual handling and lifting operations. * Safety risk to personnel and vessel in cases where transported DC may be classified as hazardous cargo containing low flash point substances.

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