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Years

Figure 45. Typical Time Table for Lease Development

[Design

Install

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IDesign

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1Install Facilities

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B.

Environmental Impact of the Proposed Sale

The development and production activity following this proposed

sale could result in a variety of impacts on the natural environment,

on

on other Gulf of Mexico resource uses, on air and water quality, land use patterns, on the social order, and on the economy. Part A of this section explained oil and gas operations in terms of exploration, development, and production activities and related structures. The intent of this section is to illustrate how routine operations and occasional accidents can result in situations leading to human and environmental impacts. Included are statistics, and where possible, examples and case histories of impacts caused by accidents and by dayto-day operations considered "unavoidable" in light of existing

regulations and operating practicies.

rence is 1, or 100%.

The probability of their occur

1.

Impacts Resulting From Day-to-Day Operations Which are
Unavoidable Under Existing Operating Practices, Regulations,
Economics and Technology

a.

Discharge of Cleaned Drilling Muds and Drill Cuttings

The drilling mud and casing programs, and drill cuttings

volume of a representative 10,000-foot offshore well were discussed in Vol. 1, Sec. III. B. 3. b. The drilling of 900-10,000-foot wells

would yield 625,500 tons of drill cuttings and 72,000 tons of

commercial mud components.

drilled to maximum depth.

This assumes maximum number of wells

Drill cuttings are, of course, composed of shattered and pulverized sediment and underlying native rock. In considering impact, it is also relevant to examine those components of the drilling mud which will be discharged. The following table (Table 34) briefly identifies these components. is based on the representative well drilling mud program used in

The reader should bear in mind that this discussion

Vol. I. Sec. III. A. 3. b. and other components, listed in Table 31

of that section, could be added in special cases.

b. Discharge of Produced Formation Water

There is no geological evidence on which the amount

of formation waters produced from wells resulting from this proposal can be predicted. Several years ago an estimate was made that all producing OCS wells offshore Louisiana (about 3,500) produced 240,000 bbl. per day of formation water. It is well known that some hydrocarbon reservoirs contain substantial amounts of water, whereas others

contain almost none.

Therefore, no predictions will be made at this time concerning the amount of formation water production which may be expected. While substantial amounts will likely be discharged into the sea, a significant proportion will also be reinjected into

subsurface formations.

Table 34.

COMPONENTS OF DRILLING MUDS WHICH ARE NORMALLY DISCHARGED INTO THE SEA

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sulfonate process;

removal of cellu- Dispersant and lose; reaction with emulsifier

chromium compounds

A light-colored montmor-
illonitic clay; slippery
sticky when wet; swells
to 10-20 times its dry
volume

Sodium hydroxide, NaOH

NONE

Corrosive in concen-
trated form; not harm-
ful after mixing into
mud at low concentra-
tion and allowed to
react

Ferrochrome salt of lig-Possible chromium
nosulfonic acid; con- toxicity in pure
tent: Fe-2.6%, Cr-3.0%, | form, none known
S-5.5%
from diluted form
in muds

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Some

The mineral content of formation waters also cannot be predicted. fields in Texas produce almost pure water whereas, as was cited in Vol. 1, Sec. III. A. 3. c., a Michigan field produced brines containing 624,798 ppm mineral salts. The average total dissolved solids of 76 samples from southern Louisiana and the Outer Continental Shelf was found to be 112,513 milligrams per liter (mg/1) with a high of 270,400 mg/1 and low of 61,552 mg/1. They commonly contain varying amounts of iron, calcium, magnesium, sodium, bicarbonates, sulphate, and chloride, with sodium and chloride being the most abundant ions. For informative purposes, the following table which shows the content of three represenative brines (formation water) from offshore Louisiana is included below (Tab. 35). They are classed as formation waters containing (1) high solids, (2) average solids, (3) low solids.

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