Revitalization of Old Fields

Leta K. Smith

IHS

Introduction As new conventional discoveries decline and with many frontier exploration opportunities become

increasingly difficult or expensive to access, companies are looking at where else new barrels might be

found. Oftentimes it is in fields that have already been discovered. Companies are loathe to abandon

fields and are always looking for ways to revitalize them. Only 13% of all oil and gas fields1 that have

ever produced have been abandoned, which is a testament to the lure of revitalization. Most fields

produce well beyond the number of years for which the original development was planned. Many

fields—even small ones— are producing well beyond 50 years (Table 1). This is possible because the

revitalization efforts result in an increase in the estimated ultimate recoverable (EUR) of the field.

Table 1. Number of fields producing today by size and years on production1

Field Size (MMboe) <20 20 to 50

50 to

100

100 to

200

200 to

500

500 to

1,000 >1,000

Years Producing ↓

<20 Years 2,916 695 433 324 248 111 87

20 to 30 Years 1,107 322 221 155 127 42 62

30 to 40 Years 695 308 181 139 135 58 70

40 to 50 Years 421 176 138 140 140 60 72

>=50 Years 524 263 176 166 190 62 98

Field Growth The act of increasing the EUR of a field is commonly referred to as field growth, and it has been study

extensively by the U.S. Geological Survey2. Studying fields outside North America, IHS3 has also found

1 Outside the United States lower-48 onshore and shallow water and Canada onshore. Source IHS.

2 See USGS Fact Sheet fs2012-3052[1] at http://energy.usgs.gov/ for more information and references

3 Research in progress

that fields tend to grow over time through various means such as infill drilling, recompletions in

different zones, waterflooding, enhanced oil recovery (EOR), or cost reductions that make more barrels

profitable. Each time abandonment looms, new technology is deployed to keep a field producing, when

possible, to continue cash flow and avoid the costly process of abandoning a field, especially those

offshore.

But deciding which technology or process to apply to a field is difficult. Many different EOR processes

may be applicable to a given field (Figure 1), and all of them require costly infrastructure to implement.

It is not uncommon for operators to study a process and pilot test if for many years before either

implementing the plan or more frequently abandoning it. And most of the EOR processes require the

field to have relatively high, well-connected porosity, leaving little that operators can do to increase

productivity and EUR in their smaller fields. However, that has changed with the unconventional

techniques adapted for shales.

Unconventional Techniques on Conventional Fields Although the unconventional techniques of horizontal wells and hydraulic fracturing have been around

for decades, they were adapted for shales. Some of the adaptions and improvements include (but are

not limited to) measurement-while-drilling, better seismic to “see” the reservoir, better drill bits and

improved geosteering to take advantage of the better seismic and keep the drill bit in very thin zones,

and higher horse-power motors to create longer lateral sections.

After the successes in shale in North America, operators have begun going back to their poorer quality

reservoirs and using these updated techniques with great success. One example is the Delaware

Sandstones in the Delaware sub-basin of the Permian Basin of West Texas and New Mexico. One

hundred thirty-one new vertical and deviated wells were drilled between 2010 and 2013, but production

from those wells was insufficient to stem the overall decline. In that same time frame, 197 horizontal

wells were drilled—not only offsetting the decline but increasing production to over 40,000 bd in 2013,

a 60% increase over 2010 levels .

IHS believes this has broad application outside of North America and estimates that an additional 141

billion barrels of oil might be unlocked from existing low-productivity fields. These unconventional

techniques are already being applied to conventional mature fields by some operators. The Saint Martin

du Bossenay field in France—where hydraulic fracturing is banned— is one example where horizontal

wells alone were used. New operators re-developed the field over a decade after it had been

abandoned and added one million new barrels to what had been a nine-million-barrel field—an 11%

increase.

One advantage of using these techniques in conventional fields is that the reservoirs are slightly better

than shales and typically in the U.S., the horizontal lengths have been shorter and fewer fracture stages

have been used, making the wells less expensive than similar wells drilled in shales. Also unlike massive

improved and enhance recovery projects, the drilling can be stopped and started as needed. Finally

these techniques open new exploration possibilities in areas where operators stopped looking for oil

and gas because the reservoirs were poor quality and the finds they did make were not commercially

viable.

Figure 1 Example technical parameter ranges for different enhanced oil recovery methods. Adapted from Taber et al, SPE 35385.