If your well appears to be a "lemon" due to huge fluid losses, it may be perfect for injecting waste - and not just cuttings.
I received an e-mail from Croatia in response to my column about reinjecting drill cuttings ("Reclaim the oil from cuttings," January 2002, p. 21).
Vladislav "Vlado" Brkic, chief engineer in the waste disposal management department of INA-Naftaplin, wrote to tell me about a paper he presented at the 23rd American Society of Mechanical Engineers Energy Sources Technology Conference and Exposition in February in Houston, Texas, titled "Waste Disposal by Injection into Deep Wells." He and two colleagues named Bozidar have developed guidelines for injecting slurries into properly designed wells for permanent waste disposal - of sulfur.
Sour lemonade
Imagine mixing sulfur powder into a 5% aqueous bentonite suspension and injecting it downhole. Why would anybody do such a thing? In the process of producing gas and condensates from the Molve, Kalinovac, Stari Gradec and Gola fields in Croatia, more than 7,548 bbl of sulfur mud is produced annually. "A great ecological problem has arisen with the disposal of such a great quantity of sulfur, after the petrochemical factory has decided not to use that slurry as a raw material for sulfuric acid production," Brkic explained. By injecting this sulfur slurry into deep wells, INA-Naftaplin has solved the problem of what to do with that sulfur, enabling increased production from these fields while protecting the potable water supply. With the large number of dry exploration wells and depleted production wells in Croatia, slurry injection of such magnitude can be maintained for some time.
Selecting suitable wells
Some of the wells that prove to be a driller's nightmare due to large volumes of lost circulation can be a dream come true for waste slurry disposal. That's when you take a lemon of a formation and turn it into lemonade.
While drilling a deep exploration well, the Legrad-1jug in Croatia, a huge volume of drilling fluid was lost in two dolomitic breccia layers. Since economically favorable accumulations of hydrocarbons were not found in that well, an openhole slurry injectivity test and logs were run to confirm the physical, lithilogical and hydrodynamic characteristics of the formations. It proved to be suitable for injecting 18,870 bbl of slurry and water at a rate of 66 gal/min to 106 gal/min and an injection pressure of 1,015 psi to 1,813 psi without fracturing.
Another exploration well, the Cremusina-1 well, drilled in 1973, never reached the planned depth due to total loss of the drilling fluid. "Closing the loss zones by cementing did not prove to be successful," Brkic said. Before abandoning the well, an injectivity test and a falloff test were performed using the dispersed sulfur slurry in 5% bentonite suspension, which was pumped directly into the open hole from a tank truck through the manifold and pressure tubing. Even though the formations were relatively shallow - 4,967 ft to 5,299 ft (1,514 m to 1,615 m) - the static reservoir pressure was much lower than the hydrostatic pressure, and the high permeability and secondary porosity made it easy to pump 12,580 bbl of sulfur slurry at very low injection pressures.
Properties of a good lemon
Geologic zones with high porosity and permeability are ideal for injecting and storing large quantities of waste slurry. At least 328 ft to 656 ft (100 m to 200 m) of impermeable cap rock is essential to protect drinking water at the surface or in shallower formations. There should be no faults in the shallower lithostratigraphic units, and cement bond logs should be run to ensure high-quality seals around the casing strings. Injectivity tests should be run (with bottomhole pressures measured in real time) to quantify the total volume and optimum flow rate of waste slurry without fracturing the formation.
Two-phase flow studies and viscosity and capillary pressure tests must be conducted in the laboratory to ensure that the waste stays put. "We tend to pay a lot of attention to the transport of waste after deep-well injection," Brkic said. His team is purchasing Swift software to simulate the flow energy, brine and radionucleide chains in porous and fractured geologic formations. This software can be applied to a variety of groundwater problems, as well as to model deep-well injection of hazardous waste and predict hazardous waste migration.
Other industrial wastes
The European Bank for Reconstruction and Development has provided funds to purchase equipment for preparing various types of coarse, hazardous waste to be ground up, mixed with an appropriate fluid and injected into Croatian wells that otherwise would be abandoned, Brkic said. In addition to heavy metals, low- and medium-radioactive waste created in health services and pharmacy industries are potential candidates for deep-well disposal, pending development of adequate government regulations.

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