This paper presents new technology and methods that were developed to enable lifting and producing low gravity, high viscosity crude from offshore fields. Relative advantages and disadvantages of several lifting, treating and transportation methods are discussed. The paper also reviews actual experiences with heavy oil production offshore southern California as well as plans for development of newly discovered heavy oil fields in the Santa Maria basin offshore central California and offshore Sicily in the Mediterranean.
During the recent energy crisis many refineries were modified to use lower quality heavy crudes for which there had not been much demand in the past. This conversion changed the market for heavy oil and brought its price closer to that for lighter crudes. As a result of this price change it became economically attractive to initiate production from heavy oil fields located offshore. Coincidental with this shift in market conditions a number of heavy oil fields were discovered offshore California and in the Mediterranean.
Heavy oil is usually referred to as a crude with gravities less than 20° AP I [1]. There are, however, few production related problems with crudes in the 17 ° to 20 ° API range and, for the purpose of this paper, heavy oil is defined as a crude with a gravity of 16 0 API or less and with viscosities greater than 400 cp at 100°F (400 mFa.s at 37.8°C) and 20 cp at 212°F (20 mFa.s at 100°C). The crude typically is lacking in the lighter ends and contains heavy metals, particularly vanadium and- nickel, and sulfur. Although very viscous, the heavy crudes do behave as Newtonian fluids, i. e. viscosity is a function of temperature only.
There are currently only a few offshore oil fields producing heavy crudes. One of these is the Beta field [2], located offshore southern California, which went on production in 1981. The field is being developed from three drilling platforms and one producing platform which are located in waterdepths ranging from 160 to 700 feet (50 to 215 m). Figure 1 depicts one of the drilling platforms and the production platform. Current production is about 20,000 barrels of oil per day production in this field comes from several different producing horizons. Gravities from individual wells range from 10 ° to 20°API depending upon the specific production interval. Average gravity is about 16 ° API.
Other, smaller, heavy oil fields in production include the Hueneme field offshore California and the Rospo Mare field offshore Italy in the Adriatic.
Several large offshore heavy oil fields are currently in the development stage. These include the Vega field, located offshore Sicily in the Mediterranean, and the Point Pedernalis and San Miguel fields offshore California in the offshore Santa Maria basin [3,4].
Gravity and viscosity of the crude from these fields are shown in Table 1 and Figure 2.
Little experience was available how to produce and transport the low gravity, high viscosity crude from these newly discovered offshore oil fields.
