RIASSUNTO
Summary
Tropical wetlands and the presence of indigenous people with an ancient culture and a strong economic dependence on natural resources made the Pedernales field an environmental and socially sensitive location. BP's challenge was to work in this area without disrupting the lives of nearby settlements while preserving the environment.
The Pedernales field was designed as a zero-discharge operation in which the main waste streams were to be reinjected. However, the initial waste-management strategy had to be changed because of operational constraints to one that also allowed waste disposal in an environmentally sound way. Waste recycling, biotreatment, and temporary offsite treatment and disposal were key processes in the new waste-management strategy.
During 5 years of operation, a total of approximately 41.5×104 m3 of exploration and production (E&P) waste were handled and disposed of successfully. Poor area drainage combined with high annual rainfall and low natural soil-supporting capacity required using unconventional tools and equipment. This was especially needed for disposing of drill cuttings.
Drill cuttings were handled by turning them into slurry with a specially designed mixer, then pumping the slurry to a distance of up to 2 km from the storage barge. The cuttings originally contained up to 6% oil and grease but degraded to 1% within approximately 180 days. This is considered a short time with the high level of soil/waste moisture saturation taken into account. Continuously monitoring water and soil with a simple on-site laboratory proved to be adequate and cost-effective for process control and for preventing pollution.
Background
The Pedernales field was granted to BP Venezuela in the framework of the marginal-fields-reactivation policy of the Venezuela State Oil Co. (PDVSA) in 1994. This field is located in the northeastern part of the country and has an approximate area of 480 km2. The drilling and production facilities are located on the mouth of Cano Pedernales, one of the main branches of the Orinoco river where it drains into the Atlantic Ocean. From 1995 to 1997, 44 wells were drilled, all directional with an average measured distance (MD) of 3600 m. To minimize the visual and environmental impact, drilling platforms were designed to contain clusters of up to 25 wells. The production facilities are divided into three well-platform clusters and two crude flow stations, both built on floating barges. Produced crude oil was stored on a marine barge, then exported.
Environment
The water flow of the river is completely dominated by the influx and reflux of the tides, giving the water the features of an estuarine environment. The content of river water chlorides range from 4000 to 12 000 mg/L depending on the season and influx or reflux of the tide. The river bank's vegetation consists of mangroves, mainly red (rhisophora mangle) and black (avicennia germinans), which reach a height of up to 30 m, forming a dense coastal forest. These trees are the basis of sediment fixation and soil formation. At the same time, they serve as shelters for a great number of birds. Additionally, the surroundings of the roots allow the embryonic development of fish and crustaceans, such as shrimp. In the river banks, approximately 3 km from the production platforms, are the villages of Capure and Pedernales, the populations of which are partially indigenous. Some individuals became part of the operation's labor force with adequate training.1
Waste-Management Plan
The waste-management plan approved by the Venezuela Ministry of Environment enclosed an operation of zero discharge. The zerodischarge ruling was issued because of the area's environmental and socioeconomic sensitivity and because of the close proximity to the traditional fishing areas of Capure and Pedernales' inhabitants. As shown in Table 1, waste disposal consisted of reinjecting all fluids with the exception of domestic waste. Because of operational problems, the produced water reinjection was postponed, and the cuttings reinjection was interrupted. Two factors forced changes in the initial plans - inadequate water-injection pumps and the failure to reinject drill cuttings in some of the originally planned wells.
Waste Balance in the Pedernales Field
During BP operations in the Pedernales field, more than 39.8×104 m3 of E&P waste were treated, disposed of, or recycled (see Table 2). In descending order of volume, the primary wastes were produced water, drilling cuttings, drilling fluids, and produced sand.
Produced Water Disposal
Pedernales' crude oil has a relatively high water/oil ratio, and typical water production ranged from 159 to 318 m3/day. Initially, the produced water was to be reinjected into the reservoir to dispose of waste in an environmentally sound manner and to enhance oil recovery at the same time. However, the available water-reinjection pumps failed to perform the task. To mitigate this situation, a tank vessel was hired that stored and later shipped the water as ballast to the Cardon refinery's treatment system, located on the west coast of Venezuela. This operation continued until the reinjection pumps were replaced. A total of 9.9×104 m3 of produced water was transported to the Cardon refinery.
Produced Sands Disposal
The production and crude-separation facilities were designed with a sand cleaning system. Nevertheless, the sand contained more than 1% hydrocarbons at the end of the process. Considering the sensitivity of the area, the sand collected in the sand washing system, and the sludge generated during pipeline cleaning, trough pigging operations had to be disposed outside the Pedernales field. Produced sand was treated and disposed of in two different ways.