As hydraulic fracturing, or fracking, operations grow worldwide, well operators are fine-tuning the process to maximize productivity and oil and gas extraction. Among the innovations to emerge are degradable fracking balls, which keep horizontal well pipes clear and disintegrate in a preset period of days or even hours with no environmental damage.
Companies such as Packers Plus Energy Services, Baker Hughes, and, most recently, Schlumberger supply degradable fracking balls. Another company, Frazier Ball Invention, filed for a U.S. patent earlier this year on a proprietary design.
Degradable fracking balls come in different sizes and withstand a range of pressures and temperatures within wells. Operators do not have to worry about retrieving them from previous operations, either by milling them out of a pipe or flushing them out with water and other fluids, thereby saving time and money. Degradable balls also prevent debris accumulation in pipes.
These devices are not brand new - initial concepts date back almost a decade. But recent developments are increasing downhole effectiveness and reliability.
Conventional non-degradable fracking balls block the well bore and seal off sections of pipe. This maximizes the pressure generated by fluids, sand, and other media that fracture oil- and gas-containing rock to extract petroleum deposits. The balls typically range in diameter from 1 to 12 in and are usually made of metal, plastics, or glass-reinforced composites. Ideally, balls are flushed out of a pipe along with the oil, gas, and fracturing media. However, they can get stuck, necessitating removal, hence the need for degradable fracking balls.
Following is a look at developments from key suppliers in this area.
The latest entrant in the market, Schlumberger, supplies a product called Elemental, which is made with a patented aluminum-based alloy that contains micro-galvanic electrochemical cells. The Houston-based company does not disclose details about the alloy or how it works, and it declined to be interviewed.
However, its technical material states that the cells derive electrical energy from a spontaneous internal chemical reaction. The oxidation-reduction reaction, as it's called, initiates dissolution of the material, rendering it a powder in days or hours, depending on ball size and downhole conditions. An Elemental ball can, for example, degrade in 1 to 12 hr in downhole temperatures above 250°F.
The balls withstand differential pressures of 10,000 psi, which is comparable to some conventional fracking balls, as well as operating conditions of 300°F.
Houston-based Baker Hughes calls its degradable balls IN-Tallic. Designed to disintegrate within 100 hr in brine (i.e., potassium chloride), the balls are manufactured with a "controlled electrolytic metallic nanostructured material" that the company says is lighter than aluminum and stronger than some mild steels. (Like Schlumberger, Baker Hughes declined to make a representative available for comment.) According to the company, electrochemical reactions controlled by the nanocoatings within the ball's composite grain structure trigger disintegration.
Packers Plus Energy Services, of Calgary, Alta., Canada, calls its degradable ball line StackFRAC. The most recent addition is the SF6D, which withstands pressures up to 10,000 psi. The product begins degrading in downhole temperatures that exceed 140°F and eventually flakes away.
A more detailed look at what could soon be an addition to the degradable ball market is seen in the patent filing from Frazier Ball Invention, of Corpus Christi, Texas. The ball is made of high-molecular-weight polyglycolic acid (PGA), which is an aliphatic polyester that is biodegradable. Trade-named Kuredux, the PGA is supplied by Japan's Kureha Corp., and it is distributed in the United States by Itochu Chemicals America, of White Plains, N.Y.
The PGA reportedly has excellent short-term stability in ambient conditions, so it can be stored with no degradation. Under the heat and pressure conditions of fracking, however, it begins to deteriorate once operations are over. Tests by the company show that a 160-g (5.6-oz) sample placed in 200°F water for four days lost almost 19 percent of its mass.
The company says that Kuredux will sufficiently degrade in 48 hr in a 250°F aqueous solution to unblock a well bore. Degradation is caused by the random hydrolysis of ester bonds, which reduces the PGA to glycolic acid, a non-polluting organic substance. The glycolic acid eventually breaks down into either glycine - the smallest of the 20 amino acids found in proteins - or carbon dioxide and water.
"Once serious degradation begins," the patent filing stated, "it can progress rapidly." Structural failure can occur in as soon as two days. Tests indicate that downhole heat and pressure transform the PGA from a hard, semi-crystalline state into a malleable amorphous composition, which loses surface mass and eventually dissolves.
Degradable fracking balls are a simple way of resolving costly well-pipe blockages. Thousands are in use around the world, and demand for them will grow as oil and gas extraction efforts increase. In the United States alone, fracking is predicted to yield 8.15 million bbl/day this year, an 18 percent increase from 2012.
Schlumberger's Elemental fracking ball uses an internal reaction to dissolve under heat.