Enhanced Recovery Under Constrained Conditions
Authors: Mungan Necmettin 
Published: December 2007

Distinguished Author 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.
Should the petroleum industry be active in enhanced recovery at all times, regardless of constraints that may prevail periodically? Before this questionis answered, a few definitions are in order. In the petroleum industry," enhanced recovery" should encompass all activities (the conception, research, development, planning, and field application) directed toward the economicincrease in ultimate recovery from energy resources. In this case, energyresources include lightand medium-gravity oils, heavy oil, natural gas, naturalgas liquids, oil sands, oil shales, methane from coal beds, and coalgasification. "Constraint" generally means low energy prices but, in reality, should include lack of expertise, lack of staff or financial resources, low orunstable prices, lack of markets, and competition for exploration oracquisition. In answer to the question posed earlier, enhanced recovery shouldbe an ongoing activity for all oil- and gas-producing companies. A time lapseof about 5 years exists from conception to application of EOR; hence, even ifprevailing conditions do not immediately favor field applications, thefollowing EOR activities should proceed. 1. Develop or acquire latest EORtechnologies and maintain the staff at a high level of expertise andpreparedness for EOR. 2. Screen all reservoirs and rank them in terms ofpriority for EOR. 3. Assign a team comprising a geologist, a geophysicist, apetrophysicist, a drilling/ completions engineer, and a reservoir engineer toreview each reservoir comprehensively and to arrive at a total understanding ofthe reservoir and its performance. 4. Identify the most suitable EOR processfor each reservoir. 5. Gather or obtain the necessary laboratory and field dataand evaluate the selected EOR process. 6. Define the cost, benefits, andprofitability of each EOR application. 7.Initiate preliminary discussions forall partner and governmental approvals and partner and governmental approvalsand licenses required.
Generally, be ready to initiate an EOR process whenconditions become favorable. process when conditions become favorable. Aboveall, think of EOR as what it really is: a necessity.
Enhanced Recovery -A Perspective
"Enhanced recovery" is often used to mean improved oil recovery only. But weshould remember that gas can also require enhanced recovery. In fairlyhomogeneous formations, with no retrograde-gas components or mobile connatewater, gas recovery is highly efficient and can reach 90% if enough wells aredrilled and the facilities are sized properly. But if the reservoir is highlystratified properly. But if the reservoir is highly stratified or fractured, contains sand/shale and gas/ water sequences, and has ultralow permeability, gas recovery can be 30% or lower permeability, gas recovery can be 30% or lowerunless optimal enhanced recovery applications are pursued during thedevelopment and the exploitation stages. For example, the number of wellsneeded, the specific locations of the wells within the gas reservoir, thecompletion techniques used, and the pressure drawdown on the individual wellsmust pressure drawdown on the individual wells must be selected carefully tooptimize the gas recovery while minimizing water production or damage to gaspermeability from water flow and fines migration in the reservoir. Let us focuson the enhanced recovery of oil only-i.e., EOR. I estimate that about 600 EORprojects were under way world-wide at the end of 1989. These projects accountedfor slightly more than l million B/D of incremental EOR oil, equivalent to some8% of what the total production would have been without EOR. (The communistcountries, the Middle East, and Africa are excluded from these figures.) Topaint a worldwide picture, the average oil recovery for all known reservoirswill be about onethird of what is estimated as initially in place. Table Isummarizes the estimated place. Table I summarizes the estimated worldwidein-place gas and oil volumes by geographic areas. Nonconventional hydrocarbonsources have been excluded from these figures; only the light- andmedium-gravity oils and the nonassociated gas are summarized. In Table 1, thePeople's Republic of China is included in Asia-Pacific; Europe includes all theUSSR and the European communist countries. If enhanced recovery can add a mere10% to the recoveries, a realistic expectation based on the industry-wideperformance in the last 2 decades, some 246 billion bbl oil and 294 Tcf gaswould be added to the proven world reserves.

Lack of Expertise
A greater understanding of the reservoir and of multiphase flow in porousmedia is required for EOR applications than for primary production. We need toknow, for primary production. We need to know, for instance, how much oil willbe left and how this oil will be distributed in the reservoir. Mostimportantly, we need to understand which EOR process will apply best under agiven set of geological and reservoir conditions. To add to the challenges, theEOR technology is evolving rapidly. For example, dramatic progress is beingmade in optimum flooding of naturally fractured reservoirs, the use ofhorizontal wells in EOR applications, seismic methods to track fluiddisplacement or saturation fronts. methods to control and to minimize gas- orwaterconing effects during EOR injection/ production phases, and the use ofmicroorganisms production phases, and the use of microorganisms in EOR. Whenconstraints force field EOR applications to proceed slowly, the development ofin-house technology and expertise should continue so that the EOR process isready for implementation as conditions change favorably. Along these lines, staff training and development are legitimate EOR activities.

Lack of Staff or Financial Resources
Perhaps two of the greatest constraints Perhaps two of the greatestconstraints preventing wider EOR applications are the preventing wider EORapplications are the lack of trained staff and the lack of adequate financialresources. Small-scale pilot tests can be carried out by outside technical helpin the form of consultants and through internal financing. Large-scale fieldapplications, however, require enormous knowhow, a core of well-trainedtechnical staff, and a large capital outlay. Companies must hire and maintainstaff at a high level of technical expertise. Along these lines, availabilityof adequate university-level undergraduate and graduate degree programs and 2-to 3-year technological schools is a must. Good laboratories, computingfacilities, and libraries are also needed for EOR.
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