The Waste Management System is validated by tracking performance indicators focusing on waste-related volumes and costs (Figure 1).
A combination of basic mechanical separation (shale shakers), dilution, and dumping of whole mud into a circulation reserve pit was utilized for solids control during drilling operations.
These types of systems required large quantities of water and drilling fluid additives, and significant expenses associated with eorwtruction and closure of a 75’ x 75’ x 6’ reserve pit.
Closure time for reserve pits of this size and design ranged from 6 to 18 months. These factors, combined with the increase in drilling activity, motivated study and implementation of a more specialized form of mechanical solids control system.The improved solids control system was developed and implemented as a result of a cooperative effort between Mobil, the dn Iling fluids company, a sohds control equipment company, and the drilling contractors.
How the Improved waste management System Works?
The improved solids control system consists of a semi-closed loop, flocculation-centrifuge dewatering process that removes solids for burial on location (Figure 2). The Chemically Enhanced Centrifuge (CEC) eliminates the 2-5 micron-size particles tlom the drilling fluid producing a lower weight, lower-solids drilling fluid, resulting in an increased rate of penetration. This method leaves only moist solids in the reserve pit with no liquid drilling fluids.
The process begins by mixing and hydrating a non-hazardous polymer (partially hydrolyzed polyacrylamide) in a liquid solution, that is then injected into tie drilling fluid between the pump and the centrifuge. Usually it enters the line just prior to a mixing manifold (joint of pip with bafiles inside).
Here the polymer is mixed with the drilling fluid which neutralizes the Hand coagulates, or groups, the solids into “flocs.” The flocs are then bound or they cling together with the polymer, and are ejected by the centrifuge, as occurs normally with largerparticles. The solids are then dumped into the reserve pit. The clear or nearly clear water is then returned to the drilling fluid system. This results in substantially less dilution water and drilling fluid additives used, compared to the previously utilized systems.
The specific mud program followed on drilling wells is as follows:
- Surface hole is drilled through the upper unconsolidated zones (“water sands”) using a non-hazardous gelflime spud mud, and casing is run and cemented to surface.
- The mud is used to drill out with and immediately watered back. A linear motion, fine-screen, double-deck shaker is used with up to 210 mesh screens, and the floe unit is used to control the viscosity to 29-30 sec,lqt. and mud weight to 8.6-8,9 ppg.
- This continues to the top of a significant unconsolidated redbed sand where a controlled drilling rate is exercised through the formation. “Sweeps” of prehydrated gel are pumped at 15-30-foot intervals. This keeps from overloading the hole with cuttings through this otherwise fast interval.
- Below the Gkn-ietq ahnost clear water drilling is resumed, and the weight is maintained as low as possible with the use of the floe unit. The semi-consolidated redbeds, the prevalent rock type drilled here, would make the mud, with its fine hydratable solids, too fast if they were not removed with the floc unit.
- Zones of salts and anhydrites are encountered next, usually increasing the salt content of the mud to 12,000-20,000mg/Clion. To keep the mud weight under 9.0 ppg, the floc unit is used in this interval. The floc unit is sometimes used in this interval to produce a “clear salty water” that is put in a storage tank to be hauled to a field disposal well. Fresh water is added to maintain volume and to control the drilling fluid weight.
- While drilling the pay zone, prehydrated gel is used, with weight still being controlled by the floe unit. This system is maintained to TD where production casing is run and cemented. On wells that are to be logged, the bentonite system fluid loss is lowered to below 12 cc’s with starch prior to drilling the pay zone.
This method works well because of the short drilling time on each well and because there is generally no problem of excessive buildup of polymer or undesirable elements in the water-phase of the drilling fluid system. Usually the drilling fluid that remains following casing and cementing operations is cleaned until it is clear water and hauled to a local Class 11injection well for disposal. Alternatively, the clarified drilling fluid is reused during a subsequent drilling operation.
The solids that are collected in the reserve pit are semi-dry (35-45% water by weight), and any excess water or drilling fluid is pumped from the pit back into the system. This allows the reserve pit to begin drying quickly and generally allows closure within two to four weeks, As a result, this system requires a smaller reserve pit (20′ x 30’x 1O’),with lower associated construction and closure costs. Use of these smaller-sized reserve pits has been favorably accepted. Although this type of system has been used successfidly elsewhere, this is the first known use of this type of solids control system.
Cost Benetit Evaluation
A comparison of drilling and production (post-drilling) related expenses between previous methods and the current system, including enhanced solids control, demonstrates a direct cost duction of $858 per well. Considering the 358 wells infill drilling program, a savings of $307M should be realized due to the implementation of this system.
Additionally, there is also a potential cost reductionof$12,600 per location on select wellsites that require protective measures due to their proximity to public or residential locations. Waste volumes, a designated performance indicator for the entire waste management system, have been reduced overall by approximately 80% with the improved solids control system. Other additional savings have yet to be quantified.
For example, accelerated reserve pit closurewill result in substantial manhour savings for production personnel in project tracking time after drilling, In addition, smaller drilling locations could result in reduced surface damage claims and the potential that a surface stormwater permit would be unnecessary (if less than a five acre site).
Waste Management Plans
The waste management plans are written documents that define company policies and practices regwding all wastes. These plans are site-specific guidance documents that identify each type of waste generated during drilling and producing operations (E&P), and describe their recommended handling and disposal practices.
The documents are user-tiiendly for on-site operations personnel who make decisions on waste disposal ( waste management plans.PDF). They begin with presentation of objectives and purpose, along with facility descriptions. The plans contain a waste handling and disposal section that specifically addresses individual wastes characterization, segregation, and disposal options. One important feature of the plans is a waste matrix that characterizes all recognized wastes and carI be used as a stand alone waste inventory for the particular site.
These plans were developed by on-site EHS (Environmental Health & Safety) and operations staffs (using company templates), in coordination with waste management experts from elsewhere in the organization.
These plans were implemented under the accountable authority of local area management (foremen and operations supervisors), where the responsibility of practice lies with the operations staffs. The workforce was familiarized with and trained on the contents and utility of the written waste management plans during on-site training sessions. Refresher training is conducted annual]y during a mandatory compliance training session.
Waste Management Certification System
A waste management certification system has been implemented that maintains updated lists of acceptable waste handlers and disposal facilities for use by operations personel in conjunction with the waste management plans. These lists are company confidentia] for competitive reasons and are, therefore, not distributed outside the organization.
Audits are conducted by a third party on waste handlers and disposal facilities to monitor compliance with local, state, and federal regulations. Waste handlers and disposal facilities can be nominated for inclusion in the system at any time by operations statll, and will be added to the approved lists tier necessary verifications have been conducted.
Key Performance Indicators
Key performance indicators are related to all processes detailed within the Waste Management System (Figure 1), and can serve as direct indicators of the continued health of such elements as general waste handling and disposal procedures. The primary waste management performance indicator tracked is a comparison of quantity of waste generated to barrels of oil equivalent produced(lbs. of waste/BOE).
Two additioml waste-related performance indicators geared towards environmental protection and compliance are: 1 ) number of reportable releases to air, water, and land; and 2) other associated costs of waste handling and disposal (waste-related accounting charge codes). These measures are designed to reduce waste generation and related liabilities, keeping in mind the concept of “what is measured can be improved. ”
For these purposes, waste volumes can be derived from hazardous and non-hazardous waste manifests, shipping tickets, waste facility invoices, production accounting records, or, as a last resort, the best estimates of facility persomel.
The total waste volumes are a combination of the total amount of wastes recycled combined with the total waste disposed off-site. The on-site disposal of non-hazardous waste, such as produced water or drilling mud, is not included as part of the waste volumes for these tracking purposes.
As a result, operations persomel are encouraged to utilize onsite disposal and recycling, thmby minimiztig the cost and potential liability of offsite disposal. Ideally, volumes of disposable waste generated should reduce as volumes of recycled waste increase.
Effective implementation of industry-best management practices for waste management in the exploration and producing environment, thereby reducing potential liability, improving compliance assurance, and decreasing overall waste related costs.
Written waste management plans, a waste management certification system, and a drilling waste minimization initiative, utiltiing technology previously unseen, have been implemented. Key performance indicators, focusing on waste volumes and costs, are tracked to validate and to provide an indicator of the relative health of the entire waste management system.
The drilling waste minimization initiative (enhanced solids control system) cuently implemented provides direct environmental and economic incentives, as well as other indirect benefits over conventional dilution or settling methods of solids control.
Environmental incentives include smaller surface area impact and less potential for biotic or hydrologic impact, due to reduced waste volumes Economic inwntives include reduced project tracking time after drilling and an estimated direct cost reduction of $307M for the 358-well program
Indirect benefits include reduced overall potential liability,more accurate formation evaluation (less sohds interference with wireline logs), minimized wellbore damage (reduced fluid loss and washout), as well as goodwill and improved relations with regulators and landowners.
It is intended that the proven strategies of this waste management system can be applied elsewhere to improve operations efficiency.