Page 63 - Environmental Control in Petroleum Engineering

Drilling and Production Operations 51

Following hydraulic fracturing, sand is often produced from the
wells. To minimize sand production, chemicals that physically stabilize
the sand around the wellbore can be injected. These chemicals include
plastics like phenol formaldehyde and epoxy resins, together with
alcohol solvents and special refined oils.

2.2.5 Natural Gas Production

As natural gas flows from the ground, it contains a variety
of impurities that must be removed before it can be sold. These
impurities are primarily water vapor, carbon dioxide, and hydrogen
sulfide. The process of removing hydrogen sulfide and carbon dioxide
is called sweetening.
Natural gas also contains fluids like propane, butane, and ethane,
which can be separated from the gas by liquefaction. These natural
gas liquids are more valuable and can be sold at higher prices. Other
materials contained in the gas stream include produced water, pigging
materials for the pipelines, filter media, fluids from corrosion treat-
ment, and solids like rust, pipe scale, and produced sand. Cooling
water and used lube oils and filters from compressors are also gener-
ated during gas treatment (American Petroleum Institute, 1989).
Natural gas is separated from produced solids and liquids by gravita-
tional forces in separators. Natural gas liquids are separated from
the lower molecular weight components by compression, absorption,
and refrigeration.
Water vapor is removed from natural gas by contact with liquid or
solid desiccants. Liquid desiccants include triethylene glycol, ethylene,
and diethylene. Solid desiccants include towers filled with alumina,
silica gel, silica-alumina beads, or molecular sieves. The water is
subsequently removed from the desiccant by heat regeneration, and
the desiccant is reused. The desiccation processes can generate wastes
of glycol-based fluids, glycol filters, condensed water, and solid
dessicants. These materials may contain low levels of hydrocarbons
and treating chemicals. Benzene and other volatile aromatics can
dissolve in glycols and be subsequently emitted when the glycol is
being regenerated for reuse.
Carbon dioxide and hydrogen sulfide are removed from natural gas
by contact with amines. The most common amines are diethanoiamine
(DBA) and monoethanolamine (MEA). Hydrogen sulfide can also be