Lower-Cost Facilities: Where Are They?
- Jean Weingarten (Consultant)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- October 2002
- Document Type
- Journal Paper
- 64 - 65
- 2002. Society of Petroleum Engineers
- 4.2 Pipelines, Flowlines and Risers, 5.4.1 Waterflooding, 4.3 Flow Assurance, 5.3.4 Integration of geomechanics in models, , 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.5 Processing Equipment, 4.4.3 Mutiphase Measurement, 4.1.6 Compressors, Engines and Turbines, 4.1.2 Separation and Treating, 4.2.3 Materials and Corrosion, 3.1.2 Electric Submersible Pumps, 4.3.1 Hydrates, 5.6.4 Drillstem/Well Testing
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Technology Today Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area,these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering.
It seems that all the large, easily accessible reservoirs have beendeveloped. The prospects we encounter now usually are smaller and, often, inmore-remote areas. New facilities must be placed in more-challenging locations- on offshore structures, in remote areas, subsea, or even downhole in thewell. Lowering facility capital costs can make marginal fields economicalanywhere. Because of ever-increasing geographical challenges and economicpressures, development of innovative and lower-cost facilities has advancedrapidly in recent years.
In early efforts to reduce facility costs, attention focused first onreducing the cost and size of key pieces of equipment, in the belief thatsmaller, lower-cost equipment was the key to reducing overall facility costs.Liquid/gas and oil/water separators were a substantial portion of the equipmentcost, size, and weight; therefore, these were targeted first. Most separatormanufacturers rushed to develop more compact separators. The use of this newequipment did reduce costs, but did not result in the anticipated magnitude ofsavings. In search of higher stakes, and in response to more challengingenvironments such as deep water, attention then turned to how these new devicescould be used as components of innovative production systems and used todebottleneck facilities that were already limited. The economic effect wasgreater, but still left room for improvement. More recently, it has beenrecognized that facility costs are driven strongly by the field conceptualdevelopment plan, which ultimately has the most influence over the finalfacility costs. By taking advantage of existing infrastructure when available,capital and operating costs can be lowered dramatically.
Reducing Process Equipment Size and Cost
Traditionally, separation of oil, gas, and water has been achieved bygravity segregation in large, heavy vessels on the surface. Recent efforts toreduce cost, size, and weight have resulted in separators that are a fractionof the size and even in some that may be placed downhole in the well or on thesea floor. This change was accomplished by adding some form of cyclonic flow,which centrifuges the fluids and enhances gravity separation beyond 1 g. Forliquid/gas separation, the spiral flow is induced passively by either internalvanes or by a tangential entry angle. Many separator manufacturers havedeveloped these more compact designs. An overview of new separation equipmentis given in Ref. 1.
Hydrocyclones and centrifuges have been used increasingly for oil/waterseparation. Hydrocyclones have no internal vanes or moving parts. Thetangential inlet and converging nozzle promote cyclonic rotation. Because oftheir small diameter, they have been adapted for downhole separation as well.However, the water cut required for successful hydrocyclone separation isrelatively high. A rule of thumb is that the stream must be at least 50 to 75%water. Also, limits exist for processing heavy oil in that the oil density isclose to that of water and oil viscosity is greater than that of water.Centrifuges for oil/water separation on the surface and rotating gas separatorsfor downhole electric submersible pumps both have rotating vanes that spin thefluids. With this equipment, the tradeoff between smaller size and increasedmaintenance costs associated with rotating equipment must be considered.However, they have a wider operating range than some of the alternative compactseparators.
Because of the large size, weight, and inspection requirements for vessels,as well as subsea and downhole space limitations, separators constructed ofpipe instead of large-diameter vessels have been developed. Some advantages arethat they can easily tie into existing piping, are typically much lower cost,can be replaced or inspected easily, are more suitable for downhole geometry,and are better for applications having high internal or external pressures.
When the purpose of separation is only for metering, and when accuracieswithin 5 to 10% are acceptable, multiphase meters, which require no separation,can be used. These meters are much smaller and lighter than test separators andcan perform more well tests in a given time period because they require lessstabilization time compared with a test separator.
In addition to separation technology, recent advances have been made indeveloping smaller gas compressors, gas dehydration units, and remotepower-generation turbines that use wellhead gas.
New Systems and Debottlenecking
New developments in remote locations have driven changes in the way thatfacilities are configured. Long distances from wells to a central processingfacility/platform have spurred the development of subsea test separators andmultiphase meters to avoid the high cost of providing a separate flowline forwell testing. Downhole or local separation can be used to reduce the energy,flowlines, and surface processing equipment that is used to handle water orstranded gas, for which there is no monetary value.
Increasingly, new discoveries are produced through existing facilities.Often, this method means that some form of debottlenecking must be used toaccommodate that extra production. Alternatively, debottlenecking opportunitiesmay exist because water or gas production has increased over time because ofdepletion, waterflood breakthrough, or coning. The first step indebottlenecking projects should be system modeling. This step will show thebottlenecks clearly as well as the effect of the proposed facility changes.Ideally, this model should combine reservoir, gathering system, andfacility-limit models because all of these are codependent. This modelingpromotes a common vision of complex systems, identifies other system responsesthat may alter the expected benefits, and quantifies the benefits of theproposed project.
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