Strontium Sulfate Scale Control by Inhibitor Squeeze Treatment in the Fateh Field

Abstract

Abstract With the increasing number of pressure-maintenance and waterflood projects throughout the world, seawater is being used more and more as the injection water. We have operated one of the oldest seawater injection projects at Bay Marchand, offshore Louisiana, since 1963. Much experience has been gained from this successful projectin the areas of corrosion and bacteria control, filter operations, and reservoir effects. More recently, we initiated an offshore seawater injection program at the Ninian field, U.K. North Sea. Water-treating requirements inherent to this offshore area have had to be considered in this project. There are similarities between the two projects but also significant differences because of differences in project size, age, and geography. Introduction The Bay Marchand field is situated off the coast of Louisiana, 55 miles (88 km) southwest of New Orleans. Development of the field in the 1950's was carried out by drilling directional wells from 12- and 24-wellplatforms and 4-well satellite units. Boreholes commonly are platforms and 4-well satellite units. Boreholes commonly are drilled at angles of 15 to 20 degrees from vertical, and lateral kickout is often 1,000 to 2,000 ft (300 to 600 m), and sometimes as much as 5,000 ft (1520 m). The six major reservoirs under injection are Miocene sand developments on the east flank of a large piercement saltdome. The injection wells are 11,000 to 12,000 ft (3350to 3660 m) deep. Porosity averages 29% and permeabilities range from less than 100 md to 2,000 md. permeabilities range from less than 100 md to 2,000 md. Pressure maintenance at Bay Marchand by using Pressure maintenance at Bay Marchand by using seawater as the injected fluid began in 1963. In 1969, Jordan et al. described the solution of subsequent problems that occurred. Since that time, very few changes problems that occurred. Since that time, very few changes have been made in the system, and the 50,000-B/D(7900-M3/d) seawater injection project has become one of the oldest and most successful. The Ninian field is located in Blocks 3/3 and 3/8 of the U.K. sector of the North Sea, 105 miles (169 km)north- east of the Shetland Islands at a water depth of approximately 460 ft (140 m). Production began near the end of 1978. The oil reservoir, which is about 10,000 ft (3050m) below sea level in Middle Jurassic sandstone, is 12 miles (19 km) long and 4 miles (6.4 km) wide, with anaverage thickness of 240 ft (73 m). The Ninian structure(Fig. 1) is a faulted block elongated along a north-south axis. The porosity and permeability average 20% and850 md, respectively. The reservoir is being developed as two separate units designated upper and lower reservoirs, the latter making up about 73% of the productive sand. Of the 108 wells planned for the field, 32 are in the upper reservoir (25 planned for the field, 32 are in the upper reservoir (25 producers and 7 injectors) and 76 are in the lower producers and 7 injectors) and 76 are in the lower reservoir (49 producers and 27 injectors). Pressure maintenance, required for economical production from this field, is accomplished by seawater injection. Seawater-treating facilities and injection pumps are located on each of the three platforms in the field. Injection pumps on the southern and central platforms are designed to deliver a total of 440,000 bbl(70 000 m3) of treated seawater per day at a discharge pressure of 4,200 psi (29 MPa). Similar pumps are pressure of 4,200 psi (29 MPa). Similar pumps are installed on the northern platform, with an initial capacity of 132,000 B/D (21 000 m3/d), expandable to 220,000B/D (35 000 m3/d). In the following, only the central and southern platforms are discussed, because operations at the northern platform began very recently. Seawater injection began at the southern platform in July 1979 and at the central platform in Dec. 1979. Discussion Bay Marchand A unit structure map, of the Bay Marchand field showing the locations of the platforms and satellite units is presented in Fig. 2. Structures AA, BB, U, W, and X are presented in Fig. 2. Structures AA, BB, U, W, and X are 12-well units, while Y and Z are 24-well units. JPT P. 2265