Page 50 - Environmental Control in Petroleum Engineering

38 Environmental Control in Petroleum Engineering

Regulations for the design and monitoring of reserves pits during
and after drilling can vary significantly with location. Unlined pits are
most commonly used for freshwater mud systems, while pits lined with
an impermeable barrier are used for salt or oil-based mud systems.
Following the completion of drilling of the well, the pits are eventually
dewatered, covered with a few feet of soil, and abandoned.
For offshore applications, steel tanks are used as reserves pits. The
solids, after being separated from the mud, are typically discharged
into the sea, where they settle to the bottom around the drilling rig.
In some areas, however, regulations require that any waste mud and
cuttings be transported to shore for disposal.

2.1.5 Site Preparation

The preparation of drilling and production sites can cause local
impact on the environment, including erosion, soil compaction, and
sterilization. The development of a drilling site involves the construc-
tion of roads to the site and a level surface at the site. This con-
struction can cause erosion. Erosion control measures like hay bales,
silt fences, riprap, and mulching can be used. Environmentally sound
construction methods are also required, such as slope controls, terrac-
ing, wing ditches, and diversion barriers.
The heavy equipment used to prepare a site can compact the soil,
preventing water and nutrients from flowing through the pore system.
This retards root development in plants and limits site restoration after
abandonment. Depending on the site, it may take decades to recover
(Powter, 1990). The level of compaction and its effects on plant growth
depend on soil type and particle size distribution. To date, no good
correlation has been developed to predict the effect of soil compaction
on plant growth. Freeze/thaw and wetting/drying cycles have shown
to be ineffective in loosening compacted soil and restoring normal
water/air circulation.
Drilling sites are often sterilized with herbicides to prevent plant
growth around the well and along rights-of-way. This reduces fire
hazards and improves aesthetic appearance, particularly where weeds are
prevalent. Depending on the herbicide and concentration used, how-
ever, treated areas can remain devoid of vegetation for many years. Often
an excessive amount has been used to ensure long-term vegetation
control with one application. When this occurs, the site becomes a