Water in, oil out. Oh, if it just were that simple.

Real waterflooding combines science and art. A PTTC workshop in May by the Texas/Southeast New Mexico Region in Midland, Tx., focused on conveying experience-based insights about “starting, fixing and managing small waterfloods.” That is important because good waterfloods still have their place in the U.S. reserves picture.

Illustrating concepts with Permian Basin examples, Bob Trentham, director of the Center for Energy and Economic Diversification at the University of Texas Permian Basin, stressed how important it was to employ an integrated multidisciplinary team when taking on a waterflood project. He cited an example from Laguna Petroleum’s Foster South Cowden Field in Ector County, Tx. (Grayburg/San Andres), in a U.S. Department of Energy-supported project in the 1990s. There were many challenges, and with
operations “as is,” it may have been abandoned by 2009.

“Fixing” this waterflood meant first understanding it. Challenges in doing so were the “Heinz 57” variety of old logs and the fact that
reservoir heterogeneity was smaller than well spacing. The solution was to use 3-D data to create synthetic porosity logs, which allowed detailed porosity maps to be developed. These maps revealed no-flow boundaries that explained historical performance and influenced the changes Laguna made. These changes worked and production responded. Laguna has since sold the field, but it still has many years of profitable life remaining.

Trentham also stressed the importance of digging for data–in well files, the production records, in state agency filings, in core
analyses and cores, and from talking to people previously involved in the waterflood. Uncovered facts often explain different facets of past waterflood performance. He also noted how bottom-hole pressure tests, water analyses, and production testing really could help explain what was happening in a waterflood.

Scott Atkinson of Exl Petroleum LP focused on the reservoir engineering aspects a team must address. He noted the importance
of “letting the reservoir talk” and “recognizing that there is an economic overprint to whatever one is looking at.” He reinforced
Trentham’s message of digging for data and doing one’s homework. Common sense questions include: What fluids were there initially? What fluids are there now, and where are they?

Understanding reservoir continuity and subzonal “correlatibility” is the key to completions, sweep efficiency and recovery. Fluid viscosities and mobility ratios control what fluids are flowing. Looking at analogy floods should be part of any study. In choosing analogies, one looks for similar reservoirs, good historical and recent production data, and something mature enough to have a discernible secondary production period.

Speaking candidly, however, Atkinson also noted that rarely was the perfect analogy found, so one must not be afraid to stretch the analogy. In doing so, though, one must be aware of where the “stretches” are and the potential impact of those stretches on any comparisons.

Atkinson listed his “top 10” list reasons why waterfloods under-perform:

• Misunderstanding reservoir heterogeneity;
• Injecting above formation fracture pressure;
• Incorrect perforations;
• High oil viscosity;
• Insufficient lift capacity;
• Early water breakthrough;
• Out-of-zone injection;
• Underestimating fill-up volume;
• Insufficient water supply; and
• Scale, bacteria, or other water quality issues that reduce injectivity.

Despite his top 10 list, Atkinson noted that waterfloods rarely failed; instead they just disappoint in one or more areas. In today’s economic environment, even less-than-ideal waterfloods can look very attractive compared with developing reserves through acquisition or drilling.

Then there are the “nuts and bolts” of operations, which was the focus for Bob Kiker, PTTC’s man in the field in the Permian Basin. Long a champion of well bore management (i.e., maintaining the well bore, which is the high-dollar investment that must remain healthy to continue to produce the oil), he relayed experience-based tips on corrosion/chemical treating, material and metallurgy selection, rod handling, tubing and rod inspection services, and surface facility design.

When the field team (chemical man, pump supplier, service rig, company man, etc.) works together, Permian Basin experience
indicates that well failure frequencies of fewer than 0.5 per well per year can be achieved, and some operators actually achieve rates of 0.25 per well per year or less.

Another area where attention should be focused is reducing power costs. These can involve either design changes or changes in operating practices. Kiker cited several examples of simple design changes that removed unnecessary pressure drops in injection systems, thus significantly lowering horsepower requirements for injection pumps.

Geology, engineering and operations all are essential to a successful waterflood. This only reinforces why PTTC workshop topics cross all disciplines.