Depleted zones are intrinsic to most mature reservoirs throughout the world. The associated issues of effective, safe and economically viable well construction, completion and workover within low pressure environments become more challenging on a daily basis. This paper discusses the application of aphron drilling fluid technology, which offers a unique alternative option that can significantly improve the operational and economic aspects for continued development of these marginal assets. The authors will detail the development of the unique micro-bubble technology and its successful application in a mature and depleted field in Mexico. Introduction When formation pressures are drawn down, the type and severity of critical operating issues are exacerbated with few solution options. When taken in combination, the operator is often faced with substantially increased costs and risk, particularly where HSE issues are concerned. The problems associated with the pressure variances encountered in mature fields, coupled with the limitations of conventional fluid and equipment technologies to properly provide an equitable solution, have driven the need for a new approach to drilling and workover operations within depleted reservoirs in mature fields. One of the latest approaches to this dilemma is the use of the aphrons drilling fluid technology. In hundreds of wells in diversified applications worldwide, the aphron technology has proven to be a viable solution within these difficult parameters. Field experience has shown that even annular pressures exceeding depleted reservoir pressures by "several thousand" psi has not hindered the creation of the micro-environment seal and mitigating invasion. This feature alone has allowed operators to eliminate casing strings, safely workover highly depleted wells and even drill into normally pressure plays on wells with existing depleted production. All of this has been affected without compromising production. Because the seal is internal to the reservoir (Fig. 1), conditions for differential sticking do not exist. In many parts of the world, this feature has successfully enabled high-angle and horizontal well construction of highly depleted reservoirs using conventional equipment. No other fluids technology in the industry enables these types of operations. Since standard wellsite fluid mixing equipment is all that is required to employ the technology, it is highly compatible with normal wellsite operations. As a drilling, completion or workover fluid, the aphron technology functions as the backbone of the operation. Serving as the bridging technology between the difficult operating parameters of mature fields and the limits of conventional equipment when employed to develop these depleted reservoirs, the aphron technology offers a solution for prolonging the economic life of these assets. Statement of Theory and Definitions Aphrons1 (micro-bubbles) are incorporated into a specifically engineered base fluid2 to aid in mitigating losses in depleted / highly permeable zones. These micro-bubbles differ significantly from aerated fluids and foams. Aphrons do not coalesce. Upon entering the lower-pressure region within a depleted formation, aphrons remain discrete, yet will agglomerate to create a stable, but easily removed, internal seal called a "micro-environment".3 Because affecting this seal requires a higher annular pressure than that of the reservoir, it readily cleans up with reservoir flow-back as production is initiated. Synergies between the various features of the technology serve to minimize fluid invasion. The easily engineered high-LSRV (low-shear-rate viscosity) properties of the base fluid are achieved with high-yield, stress-shear-thinning (HYSST) polymers. This promotes design capabilities that are well suited for optimizing diversion of annular pressures away from the depleted formations, thus minimizing whole fluid invasion. The surfactant package and the associated "meniscus-wrapping theory"1,4 provide additional invasion control. The "energized-environment"4,5 associated with aphrons employed to form the internal "micro-environment" solids-free seal and the resultant localized increase in LSRV also contributes to mitigating invasion.

BP's Gulf of Mexico (GoM) Operations have determined that the reduction of oil-on-cuttings (OOC) from 14% to less than 6.9% would provide the best opportunity to minimize the environmental impact of drilled cuttings discharge base on currently available technologies. Meeting the GoM NPDES environmental regulations, while simultaneously improving drilling performance drove the implementation of a Performance Fluids Management (PFM) process. Created within BP, PFM is a management process that integrates fluids and waste management. The new GoM cuttings discharge regulation (max 6.9% oil on cuttings) was met without adversely impacting drilling operations, while also reducing fluid cost by 8% ($3.5 MM) in 2001. This paper discusses the development and application of the PFM process. The authors will present the key components of PFM, which include implementation of a common format for fluid management programs, end-of-well recaps, a weekly PFM report capturing agreed upon performance targets, the PFM audit process, skill assessment for fluids and PFM engineers, and a model to predict accurate PFM cost/volumes generated. The PFM process has been implemented in Colombia, Bolivia and Argentina where it delivered similar savings. The process currently is being implemented in Trinidad. The process is applicable to wells in excess of $7–10 million total cost. The potential fluid cost reduction associated with a global PFM implementation will be around 10–15% ($20–25 million/year). Introduction Performance Fluids Management, or PFM as it is known by the acronym, is BP's worldwide management system for integrating drilling fluids, completion fluids, solids control, waste management and waste disposal. More than a bundling of services, PFM integrates the total fluid services into the goals of the total project. The purpose of PFM is to provide a culture of continuous improvement. This system was developed in Colombia in 1997 as a response to rising drilling costs. The Performance Fluids Management system implemented in the area focused on reducing non-productive time and the amount of waste generated onsite. Since its implementation, the PFM system has reduced the total fluids related costs by $750,000 per well in Colombia and reduced waste volumes by 41%.1 In 2001 PFM was successfully implemented in the deepwater area of the Gulf of Mexico. Initial results show an 8% reduction in operating cost. Successful implementation of the process required cooperation and teamwork from both BP and the fluid service provider. In some cases PFM required changes in work habits and culture, which do not occur over night. However, incremental behavior changes can be managed over a few months to allow everyone to embrace the new process. Once the system is in place, and improvement begins, the change to PFM gets easier. The PFM drivers are:Improve drilling performanceQA/QC in fluids / waste management and environmental impactDelivery of high value from drilling fluids and waste management contractorsAbility to track and measure performanceImplementation of a common format for fluids and waste management programs Key Elements for a Successful Implementation of PFM Process While teamwork between the operator and service supplier is crucial, at the end of the day PFM should be a process that resides within the service company. Nevertheless, it requires support and understanding from the operator for its implementation. Since PFM requires modifying habits and current work processes, several things are needed prior to beginning the implementation of Performance Fluid Management.

Meeting the new Gulf of Mexico NPDES environmental regulations (maximum 6.9% oil-on-cuttings), while simultaneously improving drilling performance has been achieved through the implementation of a Performance Fluids Management (PFM) process. This paper describes the creation and application of a fit-for-purpose GOM PFM process, which is a management process that integrates all fluids and waste management-related activities. This paper will show how the new NPDES (National Pollution Discharge Elimination System) regulation (maximum 6.9% oil on cuttings) was met without impacting drilling operations, while at the same time reducing costs 8 % ($3.5 million) in 2001. Key components of the PFM process include implementation of a common format for fluids management programs; establishing and defining key performance indicators; end-of-well recaps; a weekly PFM report capturing target and stretch performance measures; PFM audit process; skills assessment tools for fluids and PFM engineers; and a model to predict accurate PFM cost/volumes generated. In order to achieve the objective of reducing the oil-on- cuttings to meet regulatory requirements, the PFM seven-step process was utilized. This process includes expectations, analysis, modeling, setting goals, planning, execution and reviews. The reduction of oil-on-cuttings (OOC) from 14% to less than 6.9% in the GOM was a very important objective to improve the quality of the discharges to reduce environmental impact. It was very important that drilling performance should be maintained or improved. The PFM process integrates fluids and waste management. This paper discusses the application of the PFM process. The authors will present figures showing the following improvements:Reduction in days per 10,000 ftReduction in oil-on-cuttings (OOC)Reduction in downhole mud lossesReduction in actual cost compared to AFEIncreased mud recovered The PFM process has been implemented in Colombia, Bolivia, Argentina and Trinidad, where it delivered similar savings. The process is applicable to wells in excess of $7 million total cost. Introduction PFM is BP's worldwide management system for integrating drilling fluids, completion fluids, solids control, waste management and waste disposal. PFM is not a bundling of services. The purpose of PFM is to provide a culture of continuous improvement. This system was developed in Colombia in 1997 as a response to rising drilling fluids and waste management costs. The PFM system implemented in the area focused on reducing non-productive time and the amount of waste generated onsite. Since its implementation, the PFM system has reduced the total fluids related costs by $750,000 per well in Colombia and reduced waste volumes by 41%.1 Successful implementation of the process required cooperation and teamwork from both BP and the fluid service provider. PFM requires changes in work habits and culture, which do not occur over night. Once the system is in place and improvement begins the change to PFM is simplified. There are many reasons to justify implementing PFM. These include improved drilling performance, QA/QC in fluids / waste management and environmental impact, delivery of high-value from drilling fluids and waste management contractors; the ability to track and measure performance, and the implementation of a common format for fluids and waste management programs. PFM Implementation While teamwork between the operator and service supplier is crucial, at the end of the day PFM should be a process that resides within the service company. Nevertheless, it requires support and understanding from the operator for its implementation.